neuro-audio.net um032.01.005.000 ec final · 1.2. program setup to install the neuro-audio.net...

User Manual

Neuro-Audio.NET

UM032.01.005.000(26.11.2015)

Neurosoft Ltd. © 2016 5, Voronin str., Ivanovo, 153032, Russia P.O. Box 10, Ivanovo, 153000, Russia Phone: +7 (4932) 24-04-34; +7 (4932) 95-99-99 Fax: +7 (4932) 24-04-35 E-mail: [email protected] Internet: www.neurosoft.com

3

Contents

List of Abbreviations .................................................................................................. 6

Glossary ...................................................................................................................... 7

Attention!..................................................................................................................... 8

Introduction................................................................................................................. 9

1. General Principles of Working with Program ................................................. 10 1.1. System Requirements .................................................................................. 10 1.2. Program Setup ............................................................................................. 11 1.3. Program Launch........................................................................................... 14 1.4. Program Main Window ................................................................................. 14 1.5. Program Exit................................................................................................. 16

2. Quick Start ......................................................................................................... 17 2.1. General Information...................................................................................... 17 2.2. Starting New Exam....................................................................................... 18 2.3. Auditory Evoked Potentials .......................................................................... 20 2.4. Otoacoustic Emission................................................................................... 22 2.5. How to Review and Print Results ................................................................. 25 2.6. How to Review Previous Exams .................................................................. 25

3. How to Work with Exams Manager.................................................................. 26

4. New Examination............................................................................................... 27

5. Working in the Main Test Window ................................................................... 34 5.1. Working with Traces..................................................................................... 37 5.2. Quick Analysis Windows .............................................................................. 42

6. Creation of Exam Reports ................................................................................ 44 6.1. New Exam Report ........................................................................................ 46 6.2. Exam Report Template ................................................................................ 48

6.2.1. How to Edit Report Templates............................................................. 49 6.3. Clinical State ................................................................................................ 52 6.4. Conclusion.................................................................................................... 52 6.5. How to Use Tags in Report Templates ........................................................ 53

7. Program Settings .............................................................................................. 54 7.1. Global Settings ............................................................................................. 54

7.1.1. “General” Page .................................................................................... 55 7.1.2. “Software” Page................................................................................... 56 7.1.3. “Hardware” Page ................................................................................. 57 7.1.4. “Report” Page ...................................................................................... 58 7.1.5. “Exams Manager” Page....................................................................... 59 7.1.6. “Administration” Page .......................................................................... 60 7.1.7. Sites..................................................................................................... 61 7.1.8. Headphone Calibration ........................................................................ 62 7.1.9. dB SPL, nHL and HL Scales................................................................ 63

7.2. Test Template Setup .................................................................................... 64 7.2.1. Parameters .......................................................................................... 65 7.2.2. Hardware ............................................................................................. 66 7.2.3. Channels.............................................................................................. 69 7.2.4. Markers................................................................................................ 70 7.2.5. View ..................................................................................................... 71 7.2.6. Protocol................................................................................................ 72

4

7.3. Toolbar Setup............................................................................................... 73

8. AEP Tests........................................................................................................... 74 8.1. Summary Description ................................................................................... 74

8.1.1. Auditory Brainstem Response (ABR) .................................................. 74 8.1.2. Middle Latency Response (MLR) ........................................................ 75 8.1.3. Long Latency Response (LLR) ............................................................ 76

8.2. Getting Ready for Acquisition....................................................................... 76 8.3. Recommended Parameter Values ............................................................... 78 8.4. Acquisition and Analysis............................................................................... 79

8.4.1. Statistic Signal Parameters.................................................................. 83 8.4.2. Quick Analysis Windows...................................................................... 84

8.5. Test Template Settings ................................................................................ 85

9. ECochG Test...................................................................................................... 87 9.1. Summary Description ................................................................................... 87 9.2. Getting Ready for Acquisition....................................................................... 87 9.3. Recommended Parameter Values ............................................................... 88 9.4. Acquisition and Analysis............................................................................... 89 9.5. Test Template Settings ................................................................................ 89

10. TEOAE Test........................................................................................................ 90 10.1. Summary Description ................................................................................. 90 10.2. Getting Ready for Acquisition..................................................................... 91

10.2.1. OAE Probe Fitting.............................................................................. 91 10.2.2. Newborn Hearing Screening.............................................................. 94

10.3. Recommended Parameter Values ............................................................. 96 10.4. Acquisition and Analysis............................................................................. 97 10.5. Test Template Settings ............................................................................ 100

11. DPOAE Test ..................................................................................................... 101 11.1. Summary Description ............................................................................... 101 11.2. Getting Ready for Acquisition................................................................... 101 11.3. Recommended Parameter Values ........................................................... 102 11.4. Acquisition and Analysis........................................................................... 102 11.5. Test Template Settings ............................................................................ 104

12. ASSR Test ........................................................................................................ 105 12.1. Summary Description ............................................................................... 105

12.1.1. Stimulus Characteristic .................................................................... 106 12.1.2. Response Characteristic.................................................................. 107

12.2. Getting Ready for Acquisition................................................................... 108 12.3. Recommended Parameter Values ........................................................... 108 12.4. Acquisition and Analysis........................................................................... 108

12.4.1. ASSR Analysis................................................................................. 109 12.4.2. Objective Response Identification ................................................... 110 12.4.3. Audiogram Estimation...................................................................... 112

12.5. Test Template Settings ............................................................................ 114

13. Multi-ASSR Test .............................................................................................. 115 13.1. Brief Description ....................................................................................... 115

13.1.1. Stimulus Characteristic .................................................................... 115 13.1.2. Response Characteristic.................................................................. 116

13.2. Getting Ready to Acquisition .................................................................... 116 13.3. Recommended Parameter Values ........................................................... 117 13.4. Acquisition and Analysis........................................................................... 117

13.4.1. Acquisition Sequence ...................................................................... 119 13.4.2. Multi-ASSR Analysis........................................................................ 119 13.4.3. Objective Response Identification ................................................... 120 13.4.4. Audiogram Calculation..................................................................... 120

5

13.5. Test Template Settings ............................................................................ 122

14. Cognitive EP Tests.......................................................................................... 123 14.1. Brief Description ....................................................................................... 123 14.2. Preparation to Acquisition ........................................................................ 124 14.3. Recommended Parameters Values ......................................................... 125 14.4. Acquisition and Analysis........................................................................... 125 14.5. Test Template Settings ............................................................................ 127

15. Pure Tone Audiometry Test ........................................................................... 128 15.1. Brief Description ....................................................................................... 128 15.2. Preparation to Acquisition ........................................................................ 129 15.3. Recommended Parameters Values ......................................................... 130 15.4. Acquisition and Analysis........................................................................... 130

15.4.1. Manual Test ..................................................................................... 132 15.4.2. Hughson-Westlake Automatic Test ................................................. 133 15.4.3. Masking ........................................................................................... 133 15.4.4. Classification of Hearing Loss Stages ............................................. 134

15.5. Test Template Settings ............................................................................ 134 15.5.1. Manual Test Settings ....................................................................... 135 15.5.2. Automatic Test Settings................................................................... 135

16. Bone Vibrator and its Application ................................................................. 137 16.1. Applications .............................................................................................. 137 16.2. Placement ................................................................................................ 138 16.3. Masking Noise.......................................................................................... 138

Neuro-Audio.NET (User Manual)

6

List of Abbreviations

ABR – auditory brainstem response

AEP – auditory evoked potentials

ASSR – auditory steady-state response

DPOAE – distortion product otoacoustic emission

ECochG – electrocochleography

EP – evoked potentials

LLR – long latency response

MLR – middle latency response

OAE – otoacoustic emission

TEOAE – transient evoked otoacoustic emission

VEMP – vestibular evoked myogenic potentials

Glossary

7

Glossary

Exam is a data set collected during the medical examination of a patient using the Neuro-Audio device. Exam includes data from one or more tests (traces and results of their processing) and exam reports. Exams are saved in a patient card.

Exam test is a data set collected while applying a specific medical technique (e.g., TEOAE study) and processed (analyzed) as a single set. As a rule, the exam test in-cludes traces recorded from a patient and results of their processing.

Patient card contains basic data of a patient (surname, name, birth date etc.) and in-cludes any number of exams carried out at any moment by any Neurosoft device. Pa-tient cards are saved in card-files.

Card-file is a pool of any quantity of patient cards. Each card-file has a unique name and, in addition to patient cards, can contain nested card-files as well. Cards can be combined into a card-file by any feature. Well-organized card-file system will help you to put in order all the stored information and speed up the access to it.

Ipsilateral is a term corresponding to the stimulated ear.

Contralateral is a term corresponding to the ear opposite the stimulated ear.

During the acquisition with repetitive stimulation the analysis epoch means a time in-terval from the beginning of each stimulus when the digital signal from the device is converted into traces for further analysis and averaging.


8

Attention!

The device should be used only by the specialists who are trained to operate on it. It is not recommended to use the device without having the required knowledge, experi-ence and result interpretation skills.

If you have bought the computer separately, install the software before you connect the device to the computer for the first time! After the first start of the program execute Setup|Change menu command and set the correct parameters of your equipment on the “Hardware” page (see the section 7.1.3 “Hardware”), then select the default head-phones (see the section 7.1.8 “Headphone Calibration”).

If activation (i.e. the file with license key) is needed while working with the device, con-tact your dealer or Neurosoft Company and inform them about the serial number of your device to get the license key file. This file can be recorded either in the work di-rectory of the program or in the root directory of any computer disk. The license key is needed only for data recording from the device. In case the data analysis without re-cording is carried out on any computer, the license key is not needed. You can install the program and license key on any number of computers without restrictions. If the device has been changed, a new activation (i.e. a new file with license key) will be necessary. In case several Neurosoft devices are used on one computer, you will need several files with license key as well (one file for one device).

Introduction

9

Introduction

The importance of hearing in a human life cannot be overstated. If a child suffers from serious hearing impairment, his or her speech and language skills are in considerable developmental delay from a normal-hearing peer. That is why the timely and correct diagnosis of hearing impairments is very important.

The Neuro-Audio.NET program is intended for objective audiometry of children and adults by recording of biopotentials using the Neuro-Audio devices manufactured by Neurosoft Company; analysis of the recorded biopotentials (the opinion of audiolo-gist); making on-the-spot diagnosis and printing the results.

In the program the following techniques of objective audiometry are available:

Short-, middle- and long-latency auditory evoked potentials (ABR, AMLR, ALLR);

Auditory steady-state response (ASSR);

Electrocochleography (ECochG);

Vestibular evoked myogenic potentials (VEMP);

Transient evoked otoacoustic emission (TEOAE);

Distortion product otoacoustic emission (DPOAE).

The Neuro-Audio.NET program recognizes all the connected Neurosoft devices au-tomatically so you can select the device you need before the exam. The program is delivered with the Neuro-Audio devices. You can use the Neuro-Audio.NET pro-gram with the other Neurosoft devices as well, but then some audiometry techniques will be unavailable (e.g., DPOAE technique is available with the Neuro-Audio devices only). To make more detailed analysis there is also a possibility to import the exams from Neuro-Audio-Screen, the portable all-in-one ABR, DPOAE & TEOAE hearing screening system.

The adjustable graphic interface of the Neuro-Audio.NET program has been devel-oped specially for audiologists. The program is provided with all the analysis tools necessary for any audiologist: the calculation of signal statistic parameters during the acquisition; manual or automatic marking of EP components on a trace; latency and amplitude tables with calculation of asymmetry between left and right ear; construction of necessary analysis graphs.

Due to the automation of many operations doctor’s work is simplified and examination time is significantly reduced. It is especially useful when children are examined.


10

The Neuro-Audio.NET is a program which enables several users to work with it inde-pendently. Each user can easily customize the program settings for his/her own needs, including the possibility to create any number of test templates with required default settings.

1. General Principles of Working with Program

The Neuro-Audio.NET program has been developed for Microsoft Windows operat-ing system, so the general principles of working with the program don’t differ from the other applications for Microsoft Windows. Before using the program it must be in-stalled on the computer. To start working with the program you must run it.

1.1. System Requirements

Neuro-Audio.NET program supports the following operating systems (x86, x64):

Windows 7;

Windows Server 2003 SP2;

Windows Server 2008;

Windows Vista SP1 or later;

Windows XP SP2 or later.

Minimum hardware requirements:

Intel Core Duo 1.8 GHz or higher.

RAM: 1 GB or more (2 GB is recommended).

Monitor: 17" or more, resolution 1280×1024 or higher.

Free disk space: 1 GB to install the program, 1 GB or more to store the exams.

USB port to connect the device.

You can also buy the Neuro-Audio device completed with computer from Neurosoft Company. In this case, the computer is completely ready for operation with the device and all the required software is installed. If you want to use the Neuro-Audio device with some other computer, then the Neuro-Audio.NET program must be installed on it in advance. The disk with the Neuro-Audio.NET software is included in the delivery set.

General Principles of Working with Program

11

1.2. Program Setup

To install the Neuro-Audio.NET program insert the disk with software into the disk drive of your computer and wait for the installation program to start. If the auto run does not start in a few seconds, find the Neuro-Audio.NET\Neuro-Audio.NET-<version number>-Setup.exe file on the CD and start it. The Installer Language window with in-terface language selection will appear on the screen (Fig. 1.1).

Fig. 1.1. Selection of program language

After you select the program interface language, press “OK” to continue the installa-tion or “Cancel” to cancel the installation. If you continue the installation, the Neuro-Audio.NET Setup window will appear on the screen (Fig. 1.2).

Fig. 1.2. Neuro-Audio.NET welcome screen


12

Press “Next>“ to continue the installation. The “Choose Install Location” window will appear on the screen (Fig. 1.3). The program is installed in C:\Program Files\Neurosoft\Neuro-Audio.NET folder by default. To change the install location press “Browse…” and select the program location you need.

Fig. 1.3. Program install location request

Press “Next>“ to continue the installation. To return to the previous window press “<Back”. To complete the installation press “Install” in the appeared window (Fig. 1.4).

Fig. 1.4. Start Menu Folder selection


13

In the next window (Fig. 1.5) wait until the installation is completed, press “Next>“ and finally, press “Finish” in the last appeared window (Fig. 1.6) to finish the installation.

Fig. 1.5. Program installation process

Fig. 1.6. Completion of program installation

If you install the Neuro-Audio.NET program on your computer for the first time, then the Microsoft.NET and Intel IPP library, the system components required for the prop-er work of the program, will be installed on your computer by the Neuro-Audio.NET setup wizard automatically.


14

1.3. Program Launch

To run the Neuro-Audio.NET program install it on your computer in advance (see the section 1.2. “Program Setup”). In case the program has been already installed, exe-cute one of the following actions:

Double-click the program shortcut on the desktop by the left mouse button: .

Select the program in the Start menu of the operating system: Start\Programs\Neurosoft\Neuro-Audio.NET.

Run the C:\Program Files\Neurosoft\Neuro-Audio.NET\ NeuroSoft.NeuroAudio.exe file.

1.4. Program Main Window

When the program is started, the user identification window appears on the screen (Fig. 1.7). Neuro-Audio.NET is a program which enables several users to work with it independently. If you run the program for the first time, enter your login. If you run the program not for the first time, select your login from the dropdown list. If you don’t want another user to work under your login, enter a password and the program will ask you for password at each program start. In case the multiuser operation is outside your plans, check the “Do not show this window” check box at the bottom of the screen and the user identification window will not appear at further startups. To finish the identification press “OK”.

Fig. 1.7. User identification


15

When the identification is finished, the main window of the program appears on the screen (Fig. 1.8).

Fig. 1.8. Neuro-Audio.NET main window

The main window of the program represents a traditional structure common to Win-dows applications. The window title and control buttons are located at the top of the window. The main menu bar is situated immediately under the title. Using the menu commands you can create new exams and open the existing ones, control the acqui-sition, make analysis and create exam reports. Using the menu you can access all program functions. The favorite menu functions can be added to the toolbar as but-tons. The main toolbar is located under the menu bar of the program. In the Neuro-Audio.NET program there are several toolbars for acquisition, analysis, report creation etc. Each toolbar can be placed in any part of the window at user’s desire. You can adjust the visibility of the whole toolbars as well as the visibility, size and view of their separate buttons. For more details see the section 7.3. “Toolbar Setup”. In the working space of the program, occupying the rest part of the main window, the re-cording, review and analysis windows as well as the exam report editors can be situ-ated.


16

1.5. Program Exit

When your work with the program is finished, it must be closed. To exit Neuro-Audio.NET program execute one the following actions:

Press the button in the right top corner of the main window.

Select the menu command Exam|Exit.

Press the [Alt+X] key combination.

Use the button on the toolbar.

Quick Start

17

2. Quick Start

2.1. General Information

In this chapter the short instructions are given describing the sequence of user actions to execute some widely distributed techniques. They are helpful:

in case when there is no possibility to study the user manual in details;

as a prompt for those who start working with the program.

To execute one of the techniques first refer to the section 2.2. “Starting New Exam” and then to the section concerned with the necessary technique. In the text the square brackets ([ ]) mark the hotkeys which can be used instead of the described menu commands to speed up the work.

In this chapter the basic functionability of the program for acquisition and study of the bioelectric signals is described. Study the complete manual to master all the functions.

Most of the frequently used actions in the program can be carried out in several ways. For instance, to start the acquisition with repetitive stimulation you can:

use the menu command Acquisition|Repetitive stimulation; to select the menu command use either the left mouse button or the keyboard ([Alt] key is the menu activation; then you can use the arrow keys and [Enter] for selection);

use the button located on the toolbar, at the top of the screen: place the mouse

cursor on the button and click the left mouse button;

use the [Ctrl+R] key combination.

The first variant (menu command) is more understandable and can be easily found when you start working with the program. The last variants are fast and easy-to-use if you already have some experience. In this chapter all the possible variants of user ac-tions are not specified but only the main ones are described to present the information clearly.

During EP studies keep in mind that the active electrode must be connected to the negative connector (“-”) on the amplifier electronic unit which is usually black and the reference electrode must be connected to the positive connector (“+”) which is usually red. Do not forget to place the ground (common) electrode on a patient (its connector on the amplifier electronic unit is usually of green color). If the ground electrode is not available, the interference (noise) level can be too high and you will fail to get good quality signal.

Before the first exam you must execute the menu command Setup|Change and on the “Hardware” page check whether the power frequency corresponds to that of your


18

region accepted by default (for Russia – 50 Hz); then check the version of probe for otoacoustic emission. Also, please select the default headphones (see the section 7.1.8 “Headphone Calibration”).

In the following chapters it is expected that the Neuro-Audio device manufactured by Neurosoft Company is connected to the USB port of your computer.

2.2. Starting New Exam

Run the Neuro-Audio.NET program. To get more information about installation and running of the program see chapter 1 “General Principles of Working with Program”.

To start a new examination of a new patient, select the menu item Exam|New ([Ctrl+N]). In the appeared “New exam” dialog box enter patient’s basic data (op-tional) (Fig. 2.1). If you are short of time, just press “OK” ([Enter]) without entering any information.

Fig. 2.1. “New exam” dialog box

It is more convenient to enter the patient’s information in the “New exam” dialog box in the following order:

input patient’s name;

press the [Tab] key;

if patient is a woman, press the [→] key;


input the date of birth pressing the numeric keys and the key with a point to enter a delimiter character (e.g., if your patient was born on the 21st of May, 1956, just en-ter “21.5.56”); the date format set in your Windows system is used. For instance, in

Quick Start

19

some countries the symbol “/” or “-” can be used as a delimiter character or another sequence than “day-month-year” is applied;

to input the department (the number of ward, hospital etc.), press the [Tab] key and enter the required name;

to input a provisional diagnosis, press the [Tab] key and enter the diagnosis;

to select typical diagnosis from the ICD-10-CM, press the [Tab] key, then press [Enter] and select the diagnosis you need in the appeared dialog box. Then press “Add” and “OK”;

input (or select it from the dropdown list) the name of doctor making examination (this information will be used in the exam report);

to input some additional data (e.g., number of medical insurance policy, address, patient’s phone number, medical comment after examination etc.) on the “Addi-tional” page, press the [Ctrl+Tab] key combination and continue entering;

press [Enter] to close the “New exam” dialog box.

To select a test type use either the menu command Test|New or the quick-access

toolbar button . The “New test” dialog box will appear on the screen (Fig. 2.2).

Click the left mouse button on the test type you need and press “OK” (or [Enter]).

Fig. 2.2. “New test” dialog box

The dialog box of selected technique will appear in the working space of the main window. New options and toolbars specific to the selected technique will be added to the main menu.

The color markings accepted among audiologists are commonly used in the Neuro-Audio.NET program. For instance, the traces corresponding to the right ear are marked in red color and the traces corresponding to the left ear - in blue color.


20

In the following sections the work with some popular techniques of objective audiome-try are described.

2.3. Auditory Evoked Potentials

To carry out AEP studies select one of the following test types from the “New test” dia-log box:

ABR (short-latency auditory evoked potentials);

MLR (middle-latency auditory evoked potentials);

LLR (long-latency auditory evoked potentials).

Start the process of impedance measurement (the menu command Acquisition|Impedance or [Ctrl+Z]). Place the electrodes on a patient and connect them to the amplifier inputs. One amplifier channel is used by default. To specify the required number of channels and sites use the menu command Test|Template set-up. The appearance of test setup window depends on a selected technique. As for EP techniques the “Channels” page is used to customize channels and sites. Customize the settings and press “OK”. Close the impedance measurement window ([Esc]) at admissible impedance level.

Make the headphones (auditory stimulator) ready and connect them to the corre-sponding device connector. Click-type stimulus for ABR and MLR and sinewave-type (tone) stimulus for LLR are used by default. You can change the following acoustic stimulation parameters using the “Information” panel at the top of the test window:

stimulus amplitude in decibels from average auditory threshold of a healthy adult (dB nHL scale);

stimulation frequency at repetitive stimulation (Hz);

stimulated ear (left, right or both).

Start the repetitive stimulation by the menu command Acquisition|Repetitive stimulation ([Ctrl+R]) and follow the process of signal averaging. If you fail to get the required evoked potentials, you can stop averaging using the menu command Acquisition|Cancel ([Ctrl+T]) and then restart it. The menu command Acquisition|Reset can be also used to start signal averaging again (without stop of stimulation).

When you get qualitative evoked potentials, finish the acquisition and save the traces for further analysis using the menu command Acquisition|Stop. If you do not want to save the traces, press [Ctrl+T].

In EP tests the EP components are marked after acquisition automatically by default. If any components are marked inaccurately you can correct them with the mouse (press the left mouse button). But if the quantity of the marked components is not enough or if EP components were not marked automatically, then you have to mark

Quick Start

21

them manually. Click the left mouse button on the corresponding component name on the toolbar which is vertically along the left side of the screen, then shift the appeared crosshair cursor to the point of the assumed component and press the left mouse but-ton once more.

After recording all the necessary traces, you can start another technique (use Test|New menu command).

To print the results see the section 2.5. “How to Review and Print Results”.

By default, the traces of EP test are displayed in two zones: in one zone there are the traces recorded during the stimulation of the right ear and in the other zone - the trac-es recorded during the stimulation of the left ear. Moreover, all the traces can be dis-played in one working space as well. To select the display mode, use the “1<>2” but-ton in the right top corner of the test window (Fig. 2.3).

Fig. 2.3. General view of ABR test window


22

2.4. Otoacoustic Emission

To carry out OAE studies select one of the following test types from “New test” dialog box (Fig. 2.2):

TEOAE (transient evoked otoacoustic emission);

DPOAE (distortion product otoacoustic emission).

In OAE tests a special miniature ear probe with two speakers and a microphone is used as a stimulator. There is no need to place the electrodes on a patient. Acoustic signals generated by cochlea in response to stimulation from the speakers are re-corded by the microphone. Try to reduce the noise level in the room where the acqui-sition is carried out. Insert the probe in a patient’s ear in a proper way and be sure that the ear tips are of appropriate size. Connect the probe to the corresponding device connector.

To set the parameters of the technique use Test|Template setup menu command.

Start the repetitive stimulation by Acquisition|Repetitive stimulation ([Ctrl+R]) menu command. To stop averaging use Acquisition|Cancel ([Ctrl+T]) menu com-mand.

In OAE tests the acquisition is divided into two stages:

control of probe installation and stimulus volume;

acquisition (signal averaging).

During the acquisition noise level in decibels is displayed. If noise level exceeds the preset threshold (which can be changed by a slider located near the noise level indi-cator at the bottom of the acquisition window), it is colored in red. If the threshold is exceeded very often, raise the threshold or reduce the noise level in the room if it is possible. The general view of TEOAE and DPOAE acquisition windows is shown in Fig. 2.5 and Fig. 2.7.

When you get qualitative emission, finish the acquisition and save the traces for fur-ther analysis using Acquisition|Stop menu command. You can also wait for the ac-quisition to be finished automatically when the preset parameters for automatic stop are reached. The automatic stop of the acquisition can be disabled in the test tem-plate settings.

After recording all the necessary traces you can start another technique (use Test|New menu command).

To print the results see the section 2.5. “How to Review and Print Results”.

Quick Start

23

The traces of OAE test are displayed in two zones: in one zone there are the traces recorded during the stimulation of the right ear and in the other zone - the traces re-corded during the stimulation of the left ear. The general view of TEOAE test window is shown in Fig. 2.4 and the general view of DPOAE test window is shown in Fig. 2.6.

Fig. 2.4. General view of TEOAE test window.

Fig. 2.5. General view of TEOAE acquisition window.


24

Fig. 2.6. General view of DPOAE test window.

Fig. 2.7. General view of DPOAE acquisition window.

Quick Start

25

2.5. How to Review and Print Results

All the recorded traces can be analyzed after the acquisition. To select a current trace for analysis, click on it with the left mouse button. The analysis windows will refresh and the information about the selected trace will be displayed (or a table line corre-sponding to the current trace will be selected). Analysis tables and graphs are usually displayed below or alongside of the main display area of the recorded traces. To switch their visibility use View|Windows layout|Show/hide all analysis windows ([Ctrl+Shift+Tab]) menu command.

Press the [Ctrl+E] key combination to switch between all (summarized) and even/odd averaged traces. To control signal repeatability the traces are averaged in two buffers during the acquisition: the even traces are averaged in buffer A and the odd ones – in buffer B. In case the shapes of even and odd averaged traces differ significantly, it means that you probably fail to get the response.

The main method of getting the results of analysis in printed form is to generate an exam report and print it.

To create a new exam report use the menu command Report|Templates and select the template you need in the appeared submenu. To print the exam report use Report|Print ([Ctrl+P]) menu command. Before printing you can preview your exam report and make all necessary corrections (there is a possibility to edit all the contents of the exam report).

After generation of the exam report you can either continue signal acquisition in any available test or create new tests.

To finish (close) your exam use the menu command Exam|Close.

2.6. How to Review Previous Exams

To review the previous exams run the program and execute Exam|Open ([Ctrl+O]) menu command. Select the exam you need in the appeared “Exams manager” dialog box and press “Open”.

To finish your exam review, execute Exam|Close menu command.

To get more information about the exams manager, see chapter 3 “How to Work with Exams Manager”.


26

3. How to Work with Exams Manager

The examinations carried out by Neuro-Audio.NET program can be stored either in separate files or in databases. To store the exams and get access to them use the “Exams manager” program. Using this program you can create databases and patient cards, store and open the exams and save them to archive. To get more details about “Exams manager”, study the corresponding program manuals.

New Examination

27

4. New Examination

To start a new exam of a patient select the menu command Exam|New ([Ctrl+N]) or

press the button on the toolbar. The “New exam” dialog box will appear on the

screen (Fig. 4.1).

Fig. 4.1. “New exam” dialog box

In the “New exam” dialog box enter patient’s basic data (optional). If you are short of time, just press “OK” ([Enter]) without any information.


28

It is more convenient to enter the basic information in the “New exam” dialog box in the following order:

input patient’s name;


if patient is a woman, press the [→] key;


input the date of birth pressing the numeric keys and the key with a point to enter a delimiter character (e.g., if your patient was born on the 21st of May, 1956, just en-ter “21.5.56”); the date format set in your Windows system is used. For instance, in some countries the symbol “/” or “-” can be used as a delimiter character or another sequence than “day-month-year” is applied;

to input the department (the number of ward, hospital etc.), press the [Tab] key and enter the required name;

to input a provisional diagnosis, press the [Tab] key and enter the diagnosis;

to select typical diagnosis from the ICD-10-CM, press the [Tab] key, then press [Enter] and select the diagnosis you need in the appeared dialog box. Then press “Add” and “OK”;

input (or select it from the dropdown list) the name of doctor making examination (this information will be used in the exam report);

to input some additional data (e.g., number of medical insurance policy, address, patient’s phone number, medical comment after examination etc.) on the “Addi-tional” page, press the [Ctrl+Tab] key combination and continue entering;

press [Enter] to close the “New exam” dialog box.

The database does not contain card-files by default (all the exams are saved in one place). You can press “Change” and create a new card-file or select another card-file which already exists.

To add patient’s photo click on the square on the right side of the dialog box and indi-cate the image (graphic) file.

After you fill in the dialog box fields, press “OK” or [Enter].

New Examination

29

If a patient has been already examined and his/her card already exists in the data-base, the dropdown list with the similar names will appear (Fig. 4.2) while entering the name. Use either the arrow keys and [Enter] or the mouse cursor to select the name you need from the dropdown list. In this case a new exam will be saved in the existing patient card.

Fig. 4.2. Similar names of patients in the dropdown list of the database

If some patient’s details were entered with a mistake, you can correct them using the menu command Exam|Information.

So the new exam has been created. Before the examination, in the appeared “Clinical state” window (Fig. 4.3), you can enter a clinical state of the patient, his/her com-plaints or any other information you consider to be important.

Fig. 4.3. “Clinical state” window


30

To select a test type use either the menu command Test|New test or the quick-

access toolbar button . The “New test” dialog box will appear on the screen

(Fig. 4.4).

Fig. 4.4. “New test” window

Click the left mouse button on the test type you need. The “Test templates” list con-taining all the test templates of the current technique will refresh. When you choose a technique, the default template (the first in the list) is always selected automatically. All the other user templates of the technique are inherited from the default template. To select any other user template, just click on it.

To add a new test template to the selected technique press the “Add” button. To de-lete the selected test template press the “Delete” button.

The default template cannot be deleted!

To change the selected test template press the “Change” button.

When the required technique and test template in the “New test” window are selected, press “OK” (or [Enter]) to add the test to the examination.

Any tests in any order and quantity can be included in the exam. The possibility of making a particular test depends on the device delivery set.

New Examination

31

When the aforementioned actions are performed, the work window of selected tech-nique will appear in the working space of the main window (Fig. 4.5). New items and toolbars specific to the selected technique will be added to the main menu.

Fig. 4.5. Test work window.

You can directly proceed to signal recording (after placing the electrodes on a patient as it is required in the most available techniques except otoacoustic emission) using Acquisition|Repetitive stimulation menu command, however the following se-quence of actions is recommended:

If the placement of electrodes is required, start the cycle of electrode impedance measurement by Acquisition|Impedance ([Ctrl+Z]) menu command and place the electrodes (you should start with the ground electrode) simultaneously following the received impedances on the screen (Fig. 4.6).

Fig. 4.6. Electrode impedance measurement window


32

If there is too high impedance in some site, place the electrode more carefully. To fin-ish the impedance measurement, press the “Close” button or [Esc].

Before the stimulation it is recommended to start signal monitoring by Acquisition|Monitoring menu command to make sure that there are no interfer-ence and artifacts.

Set the necessary stimulation parameters using the “Information” panel at the top of the test window.

Start signal acquisition by Acquisition|Repetitive stimulation menu command. The signal acquisition window will appear on the screen. The general view of the acquisition window depends on the test type and will be described later.

During the acquisition signal averaging is applied as signal amplitude is very low in all the available techniques. Signal averaging is intended to differentiate the electrical ac-tivity evoked by repetitive acoustic stimulation (i.e. desired signal) from the noise caused by background EEG activity, muscle activity or electric inducing.

As a rule, during the acquisition, two traces are recorded simultaneously from each amplifier channel: in one trace the even epochs are averaged, in the other – the odd ones (i.e. buffers A and B). To make sure, press the [Ctrl+E] key combination when the panel with the averaged traces is in focus (click on the panel with the left mouse button if necessary). So you can switch the visibility between the summarized aver-aged trace and even/odd averaged traces (Fig. 4.7).

Fig. 4.7. Switching the visibility between summarized (left) and even/odd averaged traces (right)

To finish the acquisition and save the results use Acquisition|Stop menu command. If you don’t want to save the results use Acquisition|Cancel menu command. The more detailed sequence of actions for each test is described in the corresponding sec-tions. To switch focus between monitoring, acquisition and main windows, use the [Tab] key. To change sweep and sensitivity (vertical and horizontal scale) by one step, use the keys located in the right part of the keyboard: grey [/], grey [*], grey [+], grey [-].

To change the basic parameters quickly, use the “Information” panel (Fig. 4.8). In the left part you can enter the comments to the test and select whether this test should be copied to the report or not. To change the intensity (dB) and frequency (Hz) of stimu-lation, input the required value from the keyboard (click on the input box and type the value) or set the value using the up/down buttons located to the right of the input box.

New Examination

33

To change stimulus polarity click on the button located to the left of the intensity input box. To select the stimulated ear click on the radio button located to the right of the frequency input box. The current amplifier settings are displayed to the right of the stimulation parameters. In the right part of the panel you can see the selected auditory stimulator (headphones) and change it if it is necessary.

Fig. 4.8. Information panel

In case an error message appears during the acquisition, check the device connection to the computer and then execute Setup|Hardware reset menu command.

When signal acquisition is finished, you can start the analysis. For each technique special analysis tools are used. To get more detailed description of the analysis, see the further sections of this manual.

After test completion it is possible to start a new test of any available type using Test|New test menu command. Moreover, it is possible to return to any previous test and continue signal acquisition. It is convenient to switch between the tests by Test|Next and Test|Previous menu commands.

To save the exam, execute Exam|Save ([Ctrl+S]) menu command. To finish the ex-am execute Exam|Close menu command.

The more detailed working in the test window is described in chapter 5 “Working in the Main Test Window”, while peculiarities of signal acquisition for each test type are de-scribed in the sections corresponding to separate tests.


34

5. Working in the Main Test Window

Signal recording from a patient, traces review and analysis are carried out in the main test window.

A possible view of the main test window is shown below (Fig. 5.1). In the test window heading the current technique type is displayed (in this case – ABR test).

Fig. 5.1. Possible view of the main test window

Stimulator settings Test comment

Movable buttons with traces names

EP components markers

Analysis results table

Analysis results graph with normative data

Amplifier settings

Working in the Main Test Window

35

In the test window the data of one (current) test are always displayed. To view data of some other test use Test|Next, Test|Previous menu commands. You can also use an exam inspector located in the right side of the popup window by default (Fig. 5.2). Double-click on the test name and the test window will appear.

Fig. 5.2. “Exam inspector” popup window

Tabs with the tests can be “dragged apart” by the mouse so, that they will be dis-played in different windows. It is convenient for comparing different tests of one exam. It is carried out in the following order (Fig. 5.3):

place the mouse cursor at a test tab;

press the left mouse button and, holding it, move the mouse;

release the mouse button.


36

From now forth you can “drag” the separate tabs with tests between two analysis win-dows or “drag” them apart creating new working windows.


37

Fig. 5.3. Test windows “dragging apart”

5.1. Working with Traces

The advantage of Neuro-Audio.NET program is the possibility of simultaneous analy-sis of practically any number of traces recorded from a patient within one test.

As usual, in the center of a test window there is a place (field) to display all the traces of the test. Its view and content depend on a test type. For example, all the recorded averaged EP traces in the test will be displayed for all AEP tests and the distortion product diagram for right and left ear will be displayed for DPOAE test.

There are two display modes of the trace field:

two panels (the field is divided into two parts; the traces for right and left ear are displayed separately);

one panel (all the traces are displayed in the order they are recorded).

To switch between two display modes quickly use the “1<>2” button (for auditory EP only) located in the right top corner of the component. When you change a display mode, the traces are regrouped automatically for convenience. If two panels are dis-played, the heading indicating right and left ear traces appears above each panel. You can change the order of panels in the test settings.


38

From this moment it is assumed that all the trace actions work within one (current) panel unless otherwise specified. The current panel has darker background. To switch the focus into another panel you can:

click the left mouse button on the panel;

press [Tab] key once or several times.

To change the scales of traces use the following commands (Table 1).

Table 1. Commands to change trace scales

Parameter Menu command Hotkey

To increase sensitivity (vertical scale)

View|Sensitivity|Zoom in Numpad [+]

To decrease sensitivity (vertical scale)

View|Sensitivity|Zoom out Numpad [-]

To increase sweep (horizontal scale)

View|Sweep|Zoom in Numpad [*]

To decrease sweep (horizontal scale)

View|Sweep|Zoom out Numpad [/]

To specify scale (scale factor of a grid), it is more convenient to use dropdown lists for scales in the right top corner of the component panels (Fig. 5.4). If two panels are dis-played, their scales are always synchronized: when the scale in one panel is changed, the scale in the other panel changes as well.

Fig. 5.4. Dropdown lists to change trace scales

The color markings accepted among audiologists are commonly used in this program. The traces corresponding to the right ear are marked in red color and the traces cor-responding to the left ear - in blue color.

To the left of each trace in the window there is a button with its name (Fig. 5.1). If the trace is selected (current, focused) then the button has the heading in bold type with a dark background. Most of menu commands affect only the selected trace.


39

To make the trace current, click the left mouse button on the trace or on the adjacent button. To select several traces click the left mouse button holding the [Ctrl] key on the keyboard. All traces on the display panel can be selected by Trace|Select all menu command. To move to the next trace use Trace|Next ([Ctrl+Down]) menu command, to the previous one – Trace|Previous ([Ctrl+Up]).

To change a trace position, shifting it upward and downward on the screen, drag the button with the name by the mouse. Place the mouse cursor on the button, press the left mouse button and, holding it, move the mouse until the button is in the right place and then release the mouse button. Moreover, the position of traces on the screen can be changed by View|Traces menu command.

In fact, any current trace can be deleted by Trace|Delete ([Ctrl+Del]) menu com-mand; all traces of the test can be deleted by Test|Clear menu command; the current test can be deleted from the exam by Test|Delete command. To delete several traces simultaneously click on them with the left mouse button holding the [Ctrl] key and then execute Trace|Delete menu command. It is also possible to delete all the traces except selected ones by Trace|Delete all except selected menu command.

Any trace can be hidden and excluded from the analysis and then shown once again. To hide a trace use the Hide trace local menu command. It is convenient to switch the state of traces visibility by the window appeared while using Trace|List ([Ctrl+U]) menu command.

It is possible to show amplitude spectrum for any trace using Trace|Amplitude spec-trum menu command. The trace filter is carried out by Trace|Filter ([Ctrl+F]) menu command.

Using Trace|Calculation menu command you can carry out various mathematical operations with the traces (i.e. addition, subtraction and averaging). The commands of the menu relate to the selected traces, so you must select the traces to be used as operands first.

To control the view of markers on the traces and the information displayed next to each trace use View|Markers menu command.

If during the trace recording the active and reference electrodes were mixed up (the trace is “upside-down”), use Trace|Invert menu command to return the trace into the correct position.


40

If several traces overlapping each other (Fig. 5.5 on the left) are displayed on the screen simultaneously, it is convenient to use the mode of one trace viewing (Fig. 5.5 on the right). Double-click on the trace you need. In the quick analysis window only this trace parameters will be displayed. To return to the view mode of all traces, dou-ble-click on the trace once again.

Fig. 5.5. One trace view mode

For each trace you can enter a text comment using either Trace|Comment menu command or Trace comment local menu command activated by pressing the right mouse button.

To correct marker position on the trace, move the mouse cursor to the marker (the cursor changes its view to ) and then press the left mouse button, drag the marker

to a new place and release the mouse button. The marker can also be dragged by its heading (button). After shifting the markers, automatic renewal of quick analysis win-dows takes place (see below).

In the most of tests there is an automatic setting of analysis markers that is executed just after the corresponding trace acquisition.

In some tests separate markers on traces can be deleted, if they are not necessary, by Trace|Marker|Delete current ([Shift+Del]), Trace|Marker|Delete all on trace or Trace|Marker|Delete all menu commands.


41

For quick wave latency measuring place the mouse cursor on the trace holding the [Shift] key. Next to the mouse cursor the time will be displayed (Fig. 5.6 on the left).

Fig. 5.6. Quick latency, interval and amplitude measuring

For quick interval and/or amplitude measuring (Fig. 5.6 to the right) it is necessary to:

Move the mouse cursor to the start measuring point (e.g., to a trace peak).

Press and hold [Shift] key on the keyboard.

Press the left mouse button and, holding it, drag the mouse to the end measuring point. A rectangle with vertexes at the chosen points will appear on the screen and next to it the numeric values of the amplitude and interval will be displayed.

Thus, you can view several amplitudes (intervals) at a time if they have the common start measuring point.

To zoom any part of the trace without changing the scale of all the traces, use a spe-cial Zoom mode (Fig. 5.7). To activate Zoom mode press [Ctrl] and [Alt] buttons si-multaneously and hold them. Place the mouse cursor on the desired trace part (within the current panel with traces) and it will be zoomed. Use the mouse wheel to change the zoom.

Fig. 5.7. Zoom mode


42

5.2. Quick Analysis Windows

Quick analysis windows with tables and graphs are located by default either on the side from the window with traces or below it (Fig. 5.8).

Fig. 5.8. Quick analysis windows in the main test window

You can switch the visibility of quick analysis windows on the screen by the menu commands View|Analysis tables and View|Analysis graphs. Moreover, you can hide any analysis window just pressing the cross in the right top corner of the corre-sponding window.

To change the size move the mouse cursor to the window border and drag it by press-ing the left mouse button.

To place the windows on tabs, “catch” the window heading by the mouse, drag it to another window in the center of the appeared symbol of cross and release it (Fig. 5.9).

a) b) c)

Fig. 5.9. Placing windows on tabs


43

To drag the windows apart from tabs, “catch” the window tab by the mouse, drag it to the one of four appeared corners of the cross and release (Fig. 5.10). If you drag the window by its heading, the whole window together with tabs will be removed.

a) b) c) d)

Fig. 5.10. “Dragging” windows apart from tabs

Any window can be made as pop-up which doesn’t take place on the screen as only its heading is displayed (Fig. 5.11). To make a pop-up window click on the symbol in the right top corner of the analysis window. After that, only the heading will be visible. To view the window contents just move the mouse cursor to its heading and wait for a second – the window will pop up. If you remove the mouse cursor from the window, it will disappear. If you click on the symbol once again, the window will return to the pre-vious (not pop-up) state.

a) b)

c) d)

Fig. 5.11. Creating pop-up window


44

When selecting (focusing) a trace the corresponding line in the quick analysis window table is automatically selected. And vice versa, when selecting a line in the quick analysis window table (by the mouse or arrow keys), focusing of the corresponding trace takes place (Fig. 5.12).

Fig. 5.12. Correspondence of selected trace to certain line in quick analysis window table.

6. Creation of Exam Reports

The result of examination is an exam report. Besides text, the exam report can include tables, graphs and pictures. Each exam can include one or more reports. You can ei-ther create new (empty) reports and input the information manually or use automatic report generation by template. As a rule, one or several templates are already in-cluded in the program by default, but you can create your own templates as well.

Reports are saved in RTF format by default, but if Microsoft Word 2007 or later ver-sion is installed on your computer, then the reports can be created and stored in Mi-crosoft Word format. Use Report|Use Microsoft Word menu command for that (Fig. 6.1).

Fig. 6.1. Selection of exam report type

Creation of Exam Reports

45

The built-in report editor in many aspects is identical to the standard WordPad pro-gram in Windows. The editor has such advantages as fast work, no necessity to install additional software and good quality of the created report (Fig. 6.2).

Microsoft Word report allows obtaining access to all facilities of Word editor developed by Microsoft Company (Fig. 6.3). However, to work with this editor Microsoft Word must be installed on your computer.

To display doctor’s name in the exam report input the name in the “Doctor” input box of the exam parameters using Exam|Information menu command or input it when creating new exam (see chapter 4 “New Examination”).

Fig. 6.2. Built-in report editor


46

Fig. 6.3. Report editing in MS Word 2007

6.1. New Exam Report

To create a new (empty) exam report use Report|New menu command. The text edi-tor of the new exam report will appear on the screen (Fig. 6.4).

Fig. 6.4. Exam report editor


47

Besides the text editor field, the exam report name (“Report”) and its toolbar will be displayed on the screen. The description of toolbar buttons is shown in Table 2.

Table 2. Description of toolbar buttons.

Button Description

Print exam report

Preview before printing

Send exam report by e-mail

Search text

Replace text

Clip selected text to Clipboard

Copy selected text to Clipboard

Paste contents of Clipboard

Undo last action

Redo last action

Change current font

Current font name

Current font size

Report scale

Bold font

Italic font

Underlined font

Select font color

Select background color

Left alignment

Center alignment

Right alignment

Bullet chart

To edit report name and its comment, use Report|Properties menu option.

When you finish working with the text (printing, sending by e-mail etc.), you can close the report editor window. To save your report in the examination save this exam.


48

To open a previous report to review and edit it use Report|Open menu command, then select the report you need from the list (Fig. 6.5) and press “OK”. The exam re-port editor with the selected report text will be available (Fig. 6.4). To open a report you can use the “Exam inspector” as well.

Fig. 6.5. Opening of exam report

6.2. Exam Report Template

If you don’t want to create a report text for each exam manually, you can use report templates. A report template is the basis for exam report generation. In the template the order and type of information included into report is determined. To create an ex-am report on the base of template use Report|Templates menu command and select

a template you need from the list. You can also use the “New exam report” tool-

bar button to make the report using default template.

When the report is generated, the text editor window of the exam report with the data included in the report in the order described in the report template will appear on the screen. To change the order and type of information included into report you should edit the report template.


49

6.2.1. How to Edit Report Templates

As stated above, report templates define which information and in which order must be entered in exam report. Each template can be edited according to certain user needs. So, the report system is flexible.

To edit report templates use Reports|Templates|List… menu command. The report templates editor is shown in Fig. 6.6

Fig. 6.6. Report templates editor

At the top of the window there is a toolbar to control report templates. Using the tool-bar buttons you can create new report templates, delete report templates, import tem-plates from files, export templates to files, (e.g., to carry them to some other com-puter), rename and assign key combinations for quick report generation based on the current template. In the toolbar center there is the dropdown list of available report templates. When you select the required template from the list, you can edit it. The window of template editor is divided into three parts. On the left there is a list of infor-mation units available for the report. The information unit is called an “element”. All the elements are divided into groups which names are indicated on tabs. To select an ac-tive tab just press the left mouse button above it. To include a certain element in the report template drag it to the central part of the window with the mouse cursor.

In the central part of the window there is a list of elements included in the template. It is a tree-structured list, i.e. some elements include some other elements as well. Us-ing the toolbar above this list you can change elements order, delete, copy, clip or paste them from the Clipboard. Moreover, you can also preview the report and evalu-ate the information which will be included in your future report.


50

On the right part of the editor there is a panel of properties for the current element in-cluded in the report. Each element has its own properties. Using the panel of proper-ties on the right part of the editor you can customize any element in the list of ele-ments included in the report. The elements from the “Text formatting” group are de-scribed in Table 3.

Table 3. Description of elements for the text formatting group

Element Element description

Patient info This element is used to input patient info in the report. The element consists of several nested elements each of which is responsible for certain patient info, i.e., surname, name, age, sex, address, phone etc. To edit the element add, change or delete these nested elements.

User tag input This element is used to enter user tags (see the section 6.5. “How to use tags in report templates”) to use them in a report template text in future. When an exam report is being generated, user tag values will be requested from user. The tags in report text will be replaced by their values.

Font selection This element is used to select the font of report text.

Text color selection This element is used to select the color of report text.

Background color selection This element is used to select the background color of report text.

Alignment This element is used to align report text.

Indenting This element is used for indenting.

ТАВ This element is used to insert the ТАВ symbol in report text.

Space This element is used to insert the space symbol in report text.

Line feed This element is used to insert line feed in report text.

Line feed if not in paragraph-start This element is used to insert line feed in report text if the cursor is not in the paragraph-start.

Page break This element is used to insert page break in report text.

Text This element is used to insert some text in exam report.

RTF-file This element is used to insert the content of selected RTF-file in exam report.

RTF text This element is used to insert some formatted text in exam report. In the formatted text the tags or exam information pointers can be used, i.e., in the exam report text the $NAME tag will be replaced by patient name and the $AGE tag – by patient age. Besides tags, logic and cyclic operators can be used in formatted text. E.g., use the following conditional operator for separation by age: $IF $AGE >= 65 $THEN old $ELSE young $ENDIF, or for separation by age and sex: $IF $SEX == male && $AGE >= 65 $THEN old $ENDIF. So, only “young” or “old” lines depending on patient age will be included into report instead of these conditional operators.


51

Table 3. Continued


RTF-text (…) The conditions can be compound with logical operations &&, ||. The comparison of numeric values is carried out by >, <, >=, <=, ==, != signs. The comparison of string values is carried out by ==, != signs. The use of nested conditional operators is prohibited. The use of brackets in condition description is prohibited as well. Along with conditional operators you can use cycle structures, e.g.: $FOR $I = 0 $TO $LENGTH($ARRAYTAG) - 1 $DO $I). $ARRAYTAG[$I] $ENDFOR, where $ARRAYTAG is tag array. Conditional operators can be used inside a cycle body as well as cycles can be described inside a conditional operator.

Picture from file This element is used to insert a picture from selected file in exam report.

Table container This element is used to combine several elements in one line or in several lines. E.g., using table container you can display two or more pictures or tables side by side.

Current date and time This element is used to insert current date and time in exam report.

For example, let’s consider a report template of standard ABR test. The tree of tem-plate elements is shown in Fig. 6.7.

Fig. 6.7. Exam report template tree

Information will be inserted in the exam report in a sequential order of elements. The first element “Alignment” aligns text by center. Using the second element “Formatted text” you can add the report heading. In the settings of this element you can specify a heading text and its font. Then the left alignment of the text takes place. The element “Patient info” inputs patient info in the report according to elements contained in it.


52

The element “Cycle through all tests” inserts no information in the report by itself, but the elements contained in it will be used for each test carried out during the examina-tion. In this case, for each ABR test, its heading, traces, latency and amplitude tables for both ears as well as function graph of latency against intensity of the EP V compo-nent will be inserted in the report. It is important to note that these elements as you see from their names are used to describe AEP tests only. For the other test types these elements are ignored during the cycle.

When all the tests are described, line feed, doctor’s name and conclusion will be add-ed to the report.

Such elements as “Estimated audiogram” for right and left ear (for ASSR) as well as specific elements for the other test types can be also added to the report.

To edit the existing report templates add, delete and customize their elements. You can also create new report templates. Please, note, that to create and customize re-port template you will need plenty of time and effort but, finally, your expectations will be justified.

6.3. Clinical State

Besides the reports, “Clinical state”, another text document, is stored in examination. As a rule, the “Clinical state” document is used to describe physical condition of a pa-tient before examination. To view and edit the “Clinical state” document use the menu command Exam|Clinical state.

6.4. Conclusion

Besides the reports and “Clinical state” document, the “Conclusion” document is also stored in examination. The “Conclusion” document is used to make conclusions ac-cording to examination results. To view and edit the “Conclusion” document use Ex-am|Conclusion menu command.


53

6.5. How to Use Tags in Report Templates

In the text of report templates you can use tags to add to the report some information which is only known during a report generation (e.g., patient name and age). When the report is generated, all the tags will be replaced by their values. The list of com-mon examination tags is shown in Table 4.

Table 4. Common examination tags


$NAME Patient name

$AGE Patient age

$SEX Patient sex

$BDATE Date of birth

$REGDATE Registration date in database

$CARDCOMMENT Comment to patient card

$ADDRESS Address

$PHONE Phone

$LONGDATE Exam date (long format)

$TIME Exam beginning time

$COMMENT Comment to exam

$DIAGNOSIS Provisional diagnosis

$CARDNAME Card-file name

$CURDATE Current date

$CURLONGDATE Current date (long format)

$CURTIME Current time

$WEIGHT Patient weight (kg)

$HEIGHT Patient height (cm)

$POLICY Number of medical insurance policy

$EMAIL E-mail

$EDITUSER Doctor name

$CREATEUSER Name of doctor who created exam

$EDITDATE Last modified date

$DEPARTMENT Department

$BMI Body Mass Index

You can use the abovementioned tags in the elements of “RTF text” and “Text” tem-plates. Besides the common examination tags, some template text elements can also contain specific tags which can be used in the text of these elements only. Use the “Tags” dropdown list on the element toolbar to add tags to element text.

Using the “User tag input” template element you can enter your own tags which val-ues will be requested during report generation. User tags can be in string, numeric or list format. The string tags can be used to input optional text information to the report. The numeric tags are used to input quantitative data (e.g., individual threshold of


54

hearing for right and left ear etc.) to the report. The list tags can be used to add one of predetermined values to the report text.

7. Program Settings

User settings are saved in separate files and are loaded at the moment of user identi-fication when program is launching (see the section 1.3. “Program Launch”). The set-tings of one user can’t impact on settings of some other users. The current settings can be saved in file and retrieved from file. To save program settings in a file use the main menu command Setup|Save…. To retrieve program settings from a file use the main menu command Setup|Load….

To change interface language use Setup|Language menu command. In the ap-peared dialog box select the required language and press “OK”. The program with the selected language restarts automatically.

If several devices supported by the program are connected to your computer, select the device you need using Setup|Device selection menu command. In the appeared dialog box select the device you need and press “OK”.

To reset and then restart a connected device use the menu command Set-up|Hardware reset. It is useful if error message appears during the signal acquisition. This menu command is available if at least one exam is opened.

7.1. Global Settings

To customize main parameters of the program use the “Setup” dialog box. Select Setup|Change... menu command and the dialog box will appear on the screen.

The “Setup” dialog box consists of several pages. Look through these pages when you start working with the program.

Program Settings

55

7.1.1. “General” Page

The general view of the “General” page is shown in Fig. 7.1.

Fig. 7.1. The “General” page

“User”

“Login”. The user name to login. If several users work with the program, then each user can save his/her own settings. To add a new user, check the “Make identifica-tion” check box, restart the program and enter login and password of a new user in the appeared window.

“Password”. A keyword required at each program start. The password is used to pro-tect the program from unauthorized access. Keep in mind that it will be impossible to restore the password in case you forget it. You can leave this input box empty.

“Make identification”. If the check box is checked, user login and password will be re-quired after the program startup. There is no need to make the identification if only one user works with the program (see the sections 1.3. “Program Launch”, 1.4 “Program Main Window”).

“Protect settings with password:” If the check box is checked, the program settings are protected with the password that can be typed in the input box.

“Program start”


56

By default, no extra actions are carried out at the program startup. But if you want a new exam to be created or an existing exam to be opened automatically after the pro-gram startup, make the corresponding settings in the Program start group.

“Database”

If the “Compress data when saving to archive” check box is checked, then data com-pression while saving exams on a disk is carried out to save disk space.

“Max number of open exams:” It limits the number of simultaneously open exams in the program. You will probably need to reduce this value if you have not enough RAM on your computer.

7.1.2. “Software” Page

The general view of the “Software” page is shown in Fig. 7.2.

Fig. 7.2. The “Software” page

“Colors and markers”. You can set up trace and background colors and markers ap-pearance using “Setup…” button.

“Default exam report” – the default report template can be selected from the list.

“Load all tests on open exam (slowly)”. If the check box is checked, all tests are opened together with the exam. It is very convenient, however, it takes some time.

“Autosave on new test”. If the check box is checked, the exam is automatically saved each time the new test is created.

Program Settings

57

“Switch on device when opening exam”. If the check box is checked, the device switches on when you open the exam, thus it takes some time.

“Scale 1-2-5 for traces”. If the check box is checked, the trace scales (sweep and sensitivity) can only take values from the 1-2-5 sequence, i.e. 10 ms, 20 ms, 50 ms, 100 ms per unit, etc. If the check box is not checked, the scale is smoother: 10 ms, 15 ms, 20 ms, 25 ms, 40 ms, 50 ms, 75 ms, 100 ms per unit etc.

“Open clinical info in new exam”. If the check box is checked, “Clinical State” window is opened to enter information about patient’s state when you create a new exam.

7.1.3. “Hardware” Page

The general view of the “Hardware” page is shown in Fig. 7.3.

Fig. 7.3. The “Hardware” page

“Headphones”

“Headphones”. The type of used headphones (auditory stimulator).

Headphone calibration (see chapter 7.1.8 “Headphone Calibration”).

“OAE Probe”

“Version”. The version of OAE probe used for examination (the version is indicated on a probe label).


58

“Sensitivity (mV/Pa)”. The microphone sensitivity of OAE probe indicated on a probe label. It is used to convert micro volts received from the amplifier into pascals of acoustic pressure recorded by the probe microphone.

“OAE Probe Check” button switches on the OAE probe check mode (see Neuro-Audio technical manual).

“Mains supply”

“Mains supply frequency (Hz)”. Electric mains frequency in your region in Hz for the notch filter matching. In Russia and Europe this value equals to 50 Hz.

“Noise measurement” is a special mode of noise measurement intended for Neurosoft Ltd. service engineers to test the device, and not intended for end users.

7.1.4. “Report” Page

The general view of the “Report” page is shown in Fig. 7.4.

Fig. 7.4. The “Report” page

“Show dialog “New report”. If the check box is checked, the dialog box with report name and comment request will appear before the creation of a new exam report.

“Show glossary with the report”. If the check box is checked, the glossary window to insert most frequently used phrases quickly into the report will be displayed together with the report.

Program Settings

59

“Copy reports to folder”. If the check box is checked, the exam reports are copied si-multaneously to the selected folder of a hard disk when the examination is being saved.

“Font”. Exam report font by default. To change font style and size press the “Change...” button.

“Report templates…” button. Using this button, you can change the exam report tem-plates (see the section 6.2.1. “How to Edit Report Templates”).

7.1.5. “Exams Manager” Page

The general view of the “Exams manager” page is shown in Fig. 7.5.

Fig. 7.5. “Exams manager” page

“Data carrying over”

You can indicate the temporary storage folder and maximum storage size (see chap-ter 3 “How to Work with Exams Manager”).


60

7.1.6. “Administration” Page

The general view of the “Administration” page is shown in Fig. 7.6.

Fig. 7.6. “Administration” page.

“Administration” page allows editing the list of program users, setting the “Station name” (the computer name used when working with network database, see chapter 3 “How to Work with Exams Manager”) and other programs settings.

Program Settings

61

7.1.7. Sites

In the most of test types you must place electrodes on a patient’s head. Sites are used to determine how the electrodes are placed exactly.

Execute Setup|Sites list menu command and the “Sites” dialog box will appear (Fig. 7.7).

Fig. 7.7. The “Sites” dialog box

In this window the site names (text strings) are displayed which describe the montage of electrodes (understandable for doctors) for one amplifier channel. Several standard sites for techniques are available by default. For example, the “Cz-M” (vertex – mas-toid) site is used for short-latency auditory evoked potentials at single channel acquisi-tion. The “Cz-M1” and “Cz-M2” sites are used at double-channel acquisition for the first and the second channel, respectively.

There are two site parameters – name and side. Head side to which the site corre-sponds to (e.g., “Cz-M1”: vertex – left mastoid, “Cz-M2”: vertex – right mastoid) is used by the program at signal acquisition to recognize ipsilateral and contralateral traces automatically.

To add a new site, press the “New…” button. To change the parameters of selected site, press the “Change…” button. To delete a selected site, press the “Delete…” but-ton.


62

7.1.8. Headphone Calibration

The dialog box allowing to review and set the calibration data for the supported mod-els of headphones can be opened using Setup|Change… menu command,

“Hardware” page, button located rightward the “Headphones:” combo-box. The general view of the headphone calibration dialog box is shown in Fig. 7.8.

“Device type:” combo-box allows selection of the device manufactured by Neuro-soft Ltd, for which the calibration coefficients are displayed in the table below.

Select the headphones you need from the “Headphones:” combo-box. These head-phones will be used in each test by default (if a test is configured to use default head-phones).

Fig. 7.8. Headphone calibration dialog box

Attention! Selected headphones model (either from the “Headphones” drop-down list or in the test template settings) must always be the same one that is actually used for recording with selected device. Otherwise calibration will be wrong, and the usage of the device with wrong calibration is prohibited!

It’s recommended to keep the “Change values of coefficients” checkbox un-checked in order to protect the calibration coefficients from unintentional change. Check it and change the coefficients only when you really know what you are doing (at your own risk)!

Program Settings

63

In the table of coefficients for dB scales the coefficients for various stimuli types are displayed to transfer stimulus intensity units from dB SPL to dB HL and dB nHL which are commonly used in audiology.

7.1.9. dB SPL, nHL and HL Scales

SPL scale (Sound Pressure Level) is standard sound intensity scale (in dB) to meas-ure the sound pressure value relative to 20 µPa reference pressure.

120–130 dB SPL is pain threshold.

nHL scale is a scale (in dB) calibrated for persons with normal hearing. This scale is used for short duration stimuli (clicks and tone-bursts less than 20 ms). 0 dB accord-ing to nHL scale is the average hearing threshold of a large population of normal hear-ing adults.

HL scale is a scale (in dB) calibrated for persons with normal hearing. This scale is used for long duration stimuli (tone-bursts more than 20 ms). 0 dB according to HL scale is the average hearing threshold of a large population of normal hearing adults.

The correction coefficients (see Fig. 7.8) for SPL scale are intended to take into ac-count the frequency response characteristics of headphones. They are set on the ba-sis of the information supplied by the headphones manufacturer and can not be changed by a user.

The correction coefficients for nHL and HL scales specify dB SPL level which corre-sponds to the zero in nHL and HL scales. These coefficients depend on the type of the used headphones and stimulus frequency. Thus, to transform the stimulus inten-sity from nHL/HL to SPL, it is required to add the corresponding coefficient from the table to nHL/HL value. These calculations are performed by the program automatically according to the given table.

To adjust the intensity in nHL/HL scales correctly, it is important to select the correct type of the used heaphones (in the program settings or in the test template settings)!

If you use click as a stimulus, nHL and HL scale values are typically 30-35 dB less than SPL scale values, and the correction coefficients for nHL and HL are the same.

Since the average hearing threshold of normal hearing adults can vary depending on the region and other factors, a doctor can introduce her/his own correction coefficients for nHL and HL scales by detecting the average hearing threshold in dB SPL (in re-sponse to tone-bursts for nHL and pure tones for HL) for a group of normal hearing adults. However, in most cases it is enough to use the default settings.


64

7.2. Test Template Setup

All test settings are saved in a test template. There is a base template for each tech-nique which cannot be deleted. Using the base template you can create any number of user templates.

Use Setup|Test templates… main menu command to customize test templates for all techniques at any time. The window looking like a “New test” window (see Fig. 4.4) will appear on the screen where you can select techniques and also create, change and delete their templates.

To customize a template for current test use Test|Template setup menu command or press the corresponding button on the toolbar. The test template setup dialog box will appear on the screen (Fig. 7.9). In this dialog box there are several pages of the test settings.

In the “Parameters” page there are basic parameters of a technique divided into two groups: common and specific parameters for a certain technique.

In the “Hardware” page there are two pages with amplifier and stimulator parameters.

Using the “Channels” page you can select active amplifier channels on which the re-cord of biopotentials will be carried out during the acquisition as well as sites for each channel.

Using the “Markers” page which is available for AEP techniques only you will be able to customize analysis parameters corresponding to EP components including formu-las where they are involved in (latency, amplitude, amplitude ratio) as well as to con-trol automatic arrangement of markers on traces after acquisition.

Using the “View” page you can customize the information displayed near a trace and default scales for monitoring and acquisition traces as well as switch between one and two panel display modes of working area where the panel for right and left ear are specified.

Using the “Protocol” page you will be able to create and change protocols, i.e. the se-quence of actions carried out automatically when the start button is pressed on the “Protocol” panel. To change the visibility of protocol panel in the test window, use the “Show/hide protocol panel” toolbar button.

At the top of the window you can input the name of a test template. Moreover, you will not be able to create two templates with one and the same name.

Program Settings

65

At the very top of the window the full test type name is displayed.

Fig. 7.9. Test template setup dialog box

7.2.1. Parameters

This page (Fig. 7.9) is available for all the techniques.

The “Common parameters” (the group of parameters available for all the techniques):

“Stimulation frequency (Hz)” is a number of stimuli per second at repetitive stimulation during data acquisition from the device.

“Analysis epoch (ms)” is a time interval from the beginning of each stimulus during which digitized signal from the device is recorded in traces for further analysis and av-eraging.

“Zero after stimulus (µs)” is used to set stimulus artifact to zero (e.g., in TEOAE test this interval is excluded from the calculation of trace amplitude spectrum).

“Use random deviation of stimulus period”. If the check box is checked, then the spe-cial algorithm of random deviation of stimulus period is used to remove mains distur-bances. In many cases this algorithm is more effective than a notch filter as it doesn’t distort the averaged trace.


66

“Autostop acquisition”. If the check box is checked, then the acquisition will be stopped automatically when the preset autostop parameters are carried out. Other-wise, the acquisition is stopped manually using Acquisition|Stop menu command.

“Stop acquisition” (general autostop criteria for all the tests):

“Maximum stimuli count” - when the maximum stimuli count is achieved, the acquisi-tion will be stopped.

The specific test parameters are described in details in the following sections where the techniques are described.

7.2.2. Hardware

This page is available for all the techniques and contains the “Amplifier” (Fig. 7.10) and “Stimulator” (Fig. 7.11) pages.

In the Device string you can see the name of current Neurosoft device and its set-tings displayed in this page. The connected device (as a rule, it is a Neuro-Audio de-vice) is selected by default. In case no device is connected the settings for Neuro-Audio device are displayed by default.

The list of available devices is different for various techniques. For instance, only Neuro-Audio devices can be used for DPOAE test, but many other devices can be used for AEP test.

Fig. 7.10. The “Hardware” page with amplifier parameters in test settings

Program Settings

67

Fig. 7.11. The “Hardware” page with stimulator parameters in test settings

“Amplifier” Page

You can set the parameters either for all amplifier channels or for separate channels.

Amplifier channel parameters:

“Signal input range” is a maximum signal range at amplifier input received by the de-vice without distortion. Select input range so that it is 2-3 times higher than expected maximal signal from a patient. Too high input range values lead to the increase of noise level, too low input range values lead to amplifier off-scale and signal distortion.

“Low frequency” (HFF) is a lower cutoff frequency (high frequency filter).

“High frequency” (LFF) is a high cutoff frequency (low frequency filter).

“Notch filter” is a state of notch filter (50 or 60 Hz).

“Notch filter type”. Recursive notch filter is characterized by high noise rejection ratio but it may cause the distortion of high-amplitude responses so use it only in tests without stimulation. Adaptive notch filter is characterized by low noise rejection ratio but it doesn’t cause the distortion of responses and can be used in tests with stimula-tion.

“High harmonic filter”. Adaptive high harmonic filter is useful when noise level at high frequencies is significant.

“Sampling rate” is an AD converter sampling rate.


68

“Impedance measurement”. Green/yellow/red thresholds are set for visual color dis-play of qualitative electrode placement. These parameters are used only in the tech-niques where the placement of electrodes is required.

“Stimulator” page

At the top of the page the active audio stimulator in the test for the current device is displayed.

Stimulator parameters (for Neuro-Audio devices):

“Intensity (dB)” is stimulus amplitude. In the dropdown list on the right side you can select the intensity scale: dB SPL, nHL or HL (see the section 7.1.8. “Headphone Cal-ibration”).

“Change step (dB)” means the change of intensity in decibels at one mouse click on the “Up” or “Down” button next to the numeric field of stimulus intensity on the “Infor-mation” panel (Fig. 4.8).

“Headphones” means the headphones type. You can select the headphones by de-fault (see the section 7.1.8. “Headphone Calibration”) or select other headphones for a certain test.

“Polarity” means the selection of auditory stimulus polarities. There are three possible polarities of auditory stimuli: condensation, rarefaction and condensation/rarefaction (the last one is used to delete stimulus artifact at averaging).

“Stimulus side” is the selection of ear under stimulation.

“Masking noise on”. If the check box is checked, you can use the masking noise (noise produced by the headphone speaker opposite to the stimulated ear) and spec-ify its intensity according to stimulus level.

“Stimulus waveform” means the selection of various stimulus waveforms depending on the current device and stimulator. For example, you can select a click with desired duration or a sine curve (short tone-burst) with a preset stimulus envelope (so called “window functions”: Blackman window, rectangle etc.).

Program Settings

69

7.2.3. Channels

This page (Fig. 7.12) is available for AEP tests only. Using this page you can select the amplifier channels and placement points of electrodes (i.e. sites) corresponding to them used during the acquisition.

Fig. 7.12. The “Channels” page in test template settings


70

7.2.4. Markers

This page (Fig. 7.13) is available for AEP tests only. In this page you can create the list of EP components used in the test and select those components for which latency will be calculated. You can also specify the required intervals, amplitudes and ampli-tude ratios to be calculated and displayed in the quick analysis windows.

There are two check boxes in this page:

“Asymmetry calculation”. If the check box is checked, the asymmetry (difference) be-tween specified latencies, intervals and amplitudes of right and left ears is calculated (it is displayed in the “Asymmetry” analysis window).

“Auto-mark peaks after acquisition”. In case any markers are missed or some of them are not placed accurately, you can place and correct them manually at any time.

Fig. 7.13. The “Markers” page in test template settings

Program Settings

71

7.2.5. View

This page (Fig. 7.14) is available for all the techniques. In this page you can find these groups of parameters:

“2 Panel mode”. Using this parameter you can switch between one panel (this mode is available in AEP, ECochG and VEMP tests only) and two panel display modes (two panels correspond to the data of right and left ear) as well as change the order of panels (right/left and left/right) in two panel mode.

“Information near trace”. Using this parameter you can specify the information to be displayed near the trace.

“Trace view scales”. Using this parameter you can specify default view scales for traces in monitoring window and native and averaged traces (in acquisition).

Fig. 7.14. The “View” page in test template settings


72

7.2.6. Protocol

This page (Fig. 7.15) is available for all the techniques.

Fig. 7.15. The “Protocol” page in test template settings

Protocol means the sequence of actions carried out in the specified order. As a rule, when the protocol starts, all actions are carried out automatically so you don’t need to interfere in process. For example, using protocols you can make the search of objec-tive auditory threshold in ABR tests to be carried out automatically.

In a test template several protocols can be saved. You can switch between the proto-cols using the Test protocol dropdown list.

To rename the current protocol use the “…” button. To create a new empty protocol or delete the current one use the “New” and “Delete” buttons.

To add new actions in the Test protocol action sequence list use the “Add” button. To delete the selected action use the “Delete” button.

To move the selected action up or down the list use the corresponding “Up” and “Down” buttons.

To specify type and parameters of the selected action use the control elements of the Selected action panel. Parameters depend on action type.

Program Settings

73

7.3. Toolbar Setup

In the Neuro-Audio.NET program there is a possibility to change the size of toolbar icons (from small to large) as well as their visibility, location and view.

To setup toolbars click the right mouse button above any toolbar and then select the Setup… option from the right-click menu. Now you can customize the visibility of tool-bars in the appeared window (Fig. 7.16). Check the panels to be visible on the screen. To setup each toolbar separately, select it and then press the “Setup” button.

In the “Toolbar setup” window (Fig. 7.17) you can control the visibility of each icon of the toolbar as well as specify their order, size and view (only text, only icon, icon/text).

Fig. 7.16. Setup of toolbar visibility

Fig. 7.17. Toolbar setup


74

8. AEP Tests

8.1. Summary Description

Brain electrical activity as the basis for generation of evoked potentials has very low amplitude and is measured in micro volts. So, to record the potentials the following ac-tions must be carried out:

1. Signal amplification. As a result, the amplitude is increased by 75000–150000 times.

2. Signal averaging. As a result, the electrical activity evoked by repetitive acoustic stimulation is differentiated from the noise caused by background EEG activity, muscle activity and electric inducing.

Depending on location of generators and origin time, auditory evoked potentials (AEP) are divided into different types:

Short-latency auditory evoked potentials (ABR);

Middle-latency auditory evoked potentials (MLR);

Long-latency auditory evoked potentials (LLR).

In clinical practice ABR (auditory brainstem response) is the most popular technique for acquisition of auditory evoked potentials.

All AEP types can be used to diagnose various hearing disorders and determine threshold of hearing. Select a type of AEP on a case-by-case basis.

8.1.1. Auditory Brainstem Response (ABR)

ABR (auditory brainstem response) represents the potentials of cochlea, acoustic nerve and brainstem structures. ABR amplitude is minimal among all AEP types, so the maximal averaging is required in this test type. As a rule, the potentials are be-tween 1 -15 ms from the stimulus beginning.

The received traces usually contain a particular set of waves/peaks (called “EP com-ponents”) numerated by Roman numerals in sequence order: I, II, III, IV, V, VI, VII. It does not always happen that all peaks can be received. You can easily identify only the most permanent waves III and V as their amplitude is maximal. The studies of adults showed that they are recorded up to near-threshold sound intensity. As a rule, other ABR components appear when audio signals exceeding the sound perception threshold significantly are applied. That is why the waves III and V are the basic refer-ences in audiometry study. Even at optimum conditions of acoustical stimulation and acquisition their amplitudes exceed 0.5 µV rarely. The amplitude of other potential components is much lower.

AEP Tests

75

Amplitudes, latencies and peak amplitude ratios can be used to diagnose various hearing disorders.

Short-latency auditory evoked potentials (ABR) can be recorded successfully even at baby's first hours of life. The essential advantage of the technique is its complete in-dependence from either sleep or wakefulness state of a patient.

The weak points of objective audiometry according to the data of ABR acquisition are:

Low frequency specificity of received information.

Significant configuration distortion of potentials and decay of their amplitude in des-cant deafness patients when low-frequency stimuli of reversed polarity (500 Hz) are used. In such cases fixed polarity stimuli must be used which lead to bad distortion at the trace beginning because of electrical stimulus artifact.

This technique is especially useful at examination and screening of newborns and ba-bies as they are prohibited to be examined by subjective audiometry techniques. A wideband click is usually used as a stimulus.

Using ABR technique you can detect type and depth of hearing loss at certain fre-quencies (if a short tone-burst is used as a stimulus). With ABR technique you will be able to detect acoustic neuroma and other nervous system diseases in particular con-nected with acoustic nerve and brainstem.

8.1.2. Middle Latency Response (MLR)

MLR (middle latency response) represents AEP components between 10-50 ms from the stimulus beginning directly after ABR and before LLR. The primary auditory cortex is expected to be the major MLR source. As with ABR technique, either clicks or short tone-bursts can be used for stimulation in MLR technique. The components (peaks) on MLR trace are: Na (15–30 ms), Pa (30–40 ms), Nb (40–50 ms), Pb (50–60 ms). The positive peaks are marked as P, the negative ones – as N.

Na and Pa peaks are the basic references in audiometry study as their thresholds of appearance are approximately equal and practically correspond to sound perception thresholds. MLR peak-to-peak amplitudes are 1-2 µV.

Middle-latency auditory evoked potentials (MLR) can be recorded at baby's first hours of life, though the threshold of newborns can be higher than the threshold of adults (about 30–40 dB nHL). But to the end of the first month of life their MLR configuration and thresholds are already near MLR values of adults. MLR (as ABR) technique is quite independent from either sleep or wakefulness state of a patient. The lowering of its amplitude can be recorded in deep anesthesia only.

MLR technique is characterized by high frequency specificity so there is a possibility to study auditory thresholds within 500-4000 HZ with a high degree of confidence.


76

8.1.3. Long Latency Response (LLR)

LLR (long latency response) represents AEP components between 50-300 ms from the stimulus beginning after ABR and MLR. These potentials are the response of auditory cortex. As a rule, only short tone-bursts are used for their acquisition. The fre-quency of LLR response is very low (lower than 30 Hz). The LLR components (peaks) are: P1 (50–80 ms), N1 (100–150 ms), P2 (150–200 ms), N2 (180–300 ms). P1, N1 and P2 waves are of main interest for audiometry study.

LLR technique is characterized by the maximal amplitude among all AEP techniques which is usually about 2–10 µV. The latency period of peaks is rather variable and de-pends on patient’s age and stimulation intensity.

In ideal experiments LLR visual detection thresholds are near psychoacoustic auditory thresholds. But the response identification can be impaired by many factors.

As a rule, Long-latency auditory evoked potentials (LLR) cannot be recorded from newborns and first year babies. Only in 12-13 years LLR configuration and latency pe-riods of a child are equal to LLR of adults. The LLR appearance thresholds and ampli-tude characteristics are strongly dependent on wakefulness state of a patient. The at-tention factor (i.e. when a patient is listening to audio signals carefully) has a signifi-cant effect on them as well. If a patient is under sedation, the cortical response ampli-tude can be lowered significantly, while anesthesia leads to their total disappearance. That is why, in spite of its high frequency specificity, you can use LLR technique with children for audiometry study in a limited number of cases only.

8.2. Getting Ready for Acquisition

At acquisition of evoked potentials with any modality, it is very important to achieve low interference level in the room. The device and computer must be safely grounded. Big electric motors, welding devices and other powerful electric devices, working nearby, are prohibited.

As a rule, an audiometry study with ABR or MLR acquisition is carried out just after feeding, when a baby is sleeping. In case a child is more than six month from birth or an adult patient is under examination, ABR and MLR can be recorded either in the state of wakefulness (physical rest must be observed) or in light medication sleep.

AEP Tests

77

Fig. 8.1 shows an example of poor electrode positioning: big loops, made up by wires, work as antenna and cause high interference level. Fig. 8.2 shows perfect electrode positioning: twisted wires prevent forming of big loops and allow to lower interference level. While placing electrodes it is recommended to place wires from a patient as close to each other as possible. It is not necessary to twist wires, but it can help when the evoked potentials are not detected because of high interference level.

Fig 8.1. Poor electrode positioning

Fig. 8.2. Perfect electrode positioning

On the device electronic unit there are touch-proof connectors for each amplifier channel in the form of separate (red “+” and black “-“) round pin sockets. If you use only one of the amplifier channel outputs, then the electrodes of the other output must be disconnected. Otherwise, the interference level can increase many times.

Usually at auditory EP acquisition the electrodes are placed on a patient in the follow-ing way (in case you use one amplifier channel):

inverting (-): ipsilateral (tested) mastoid;

non-inverting (+): vertex (Cz) or the middle line of forehead on the hair growth bor-der (Fpz);

ground (common): contralateral mastoid.

When testing both ears using 2-channel recording, the non-inverting electrodes are placed on the mastoids (channel 1 – on the left mastoid, channel 2 – on the right mas-


78

toid), the ground electrode – on a forehead (Fpz), and two inverting electrodes are combined by Y-adapter and placed on a vertex (Cz).

During middle-latency and long-latency auditory EP acquisition some researchers pre-fer to swap the non-inverting and inverting electrodes so that negative peaks on the recorded trace are directed upward.

For AEP acquisition the use of surface electrodes is sufficient. Clean the places of electrode placement and get them ready for acquisition, polishing carefully by abra-sive paste to lower the impedance and get more accurate recording.

8.3. Recommended Parameter Values

The recommended parameter values for ABR acquisition are shown in Table 5.

Table 5. Values of ABR acquisition parameters

Stimulus: 100 µs click or short tone-bursts (window functions can be used for frequency band reduction)

Stimulation frequency: 10 Hz or 20 Hz (low frequencies improve I wave)

Polarity: Condensation/rarefaction (rarefaction improves I wave and condensation improves form of response, but in this case stimulus artifact is not deleted)

Intensity: 80–95 dB nHL for neurodiagnosis; 90 dB nHL up to zero to search auditory thresholds

Filters: 30–3000 Hz (100–3000 Hz for adults, 30–1500 Hz for newborns)

Analysis epoch: 10–20 ms (10 ms for adults, 20 ms for children)

Number of stimuli: 1000–4000

The recommended parameter values for MLR acquisition are shown in Table 6.

Table 6. Values of MLR acquisition parameters

Stimulus: 100 µs click for neurodiagnosis; 2-1-2 tone-burst for audiometry

Stimulation frequency: 7.1 Hz

Polarity: Condensation/rarefaction

Intensity: 70 dB nHL, if intensity is higher it can cause muscle artifacts; low intensities can be used to search auditory thresholds

Masking noise: 50 dB, only if intensity > 70 dB nHL

Filters: 10–1500 Hz or 10–200 Hz

Analysis epoch: 100 ms

Number of stimuli: 1000

AEP Tests

79

The recommended parameter values for LLR acquisition are shown in Table 7.

Table 7. Values of LLR acquisition parameters

Stimulus: 50 ms tone-burst

Stimulus tone frequency: 500 – 8000 Hz, if required

Stimulation frequency: 1.1 Hz

Polarity: Condensation/rarefaction

Intensity: 100 dB SPL

Filters: 0.1 – 10 Hz



If excessive electrical line noise takes place during AEP acquisition, you can switch on the adaptive notch filter.

8.4. Acquisition and Analysis

For AEP acquisition, after a new exam creation, in the “New test” window select the corresponding technique and template from the test templates list. For example, for ABR technique two templates are available by default: for single and double-channel acquisition.

At double-channel acquisition with the stimulation of one ear the ipsilateral (the “i” char is added to a trace name) and contralateral (the “c” char is added to a trace name and the contralateral trace is marked in black) traces are recognized by the program automatically.

According to the color markings accepted among audiologists the traces correspond-ing to the right ear are marked in red color and the traces corresponding to the left ear - in blue color.

Start the process of impedance measurement, place the electrodes on a patient and connect them to the amplifier input. Close the impedance measurement window ([Esc]) at admissible impedance level.

Connect the headphones to the amplifier unit. Set the required initial values of stimu-lus parameters on the “Information” panel.

If desired, before acquisition you can start the signal monitoring window by Acquisition|Monitoring menu command and follow the signal level received from electrodes and the presence of interference.

Start acquisition with repetitive stimulation using Acquisition|Repetitive stimulation ([Ctrl+R]) menu command and follow the process of signal averaging. If you fail to get the required evoked potentials, you can stop averaging by Acquisition|Cancel ([Esc]) menu command and then restart it. To stop the stimulation for some time use Acquisition|Pause [space key] menu command.


80

The view of the ABR acquisition window (by default) is given in Fig. 8.3.

Fig. 8.3. ABR acquisition window.

The ABR acquisition window can be divided into three parts (from top to bottom):

Averaging information panel;

Trace displaying area;

Histogram of traces quality.

Averaging information panel indicates the number of averaged and rejected traces (by quality level) and also the statistic parameters (if they are normal, they are colored green, otherwise, they are marked red).

Trace displaying area shows the averaged traces. Also, the cursor indicating the cur-rent latency is displayed near the mouse pointer.

Histograms of traces quality are displayed only if weighted averaging is activated in the test settings (which is default only for ABR test). They reveal the traces distribution by the quality level (for each channel). The trace quality is calculated using the special algorithm. When using weighted averaging, all the traces are averaged, with different

AEP Tests

81

weights applied to them depending on their quality. However, a user can interfere with the averaging process by moving (using the mouse) the slider of trace quality thresh-old (black horizontal line on the histogram). Slider position reflects the minimum trace quality accepted to the weighted averaging. Changing it sometimes can result in the improvement of the received EP. So, all the traces with poorer quality (below the qual-ity threshold) are excluded from the weighted averaging and indicated with the red color on the histogram, and those traces with the quality exceeding the threshold are included in the averaging and marked with the green color.

During the acquisition one can reset (restart) the averaging by any channel (or all of them at once). It can be useful to avoid stopping the averaging, for example, if the electrode has fallen off.

It can be done using one of the three ways:

1. Press button (“Averaging reset (restart)”) on the histogram of the trace

quality for the corresponding channel.

2. Click the button near the averaged trace with the right mouse button and se-lect item (“Averaging reset (restart)”) in the context menu.

3. Select Acquisition|Reset menu item to reset the averaging by all channels at once.

By default, the acquisition will stop automatically after a while and the averaged trace will be saved. The stop of acquisition depends on several parameters in test template settings. Firstly, the automatic stop must be switched on (otherwise, you can stop av-eraging only manually using the menu command Acquisition|Stop). Secondly, irre-spective of the statistic parameter values, the averaging will last at least minimum number of epochs specified in a template. Thirdly, if the values of statistic parameters (the certain ones are set in a template) are better than their preset thresholds, the av-eraging stops. Fourthly, if the averaging lasts up to the maximum number of epochs specified in a template, it stops immediately.

In fact, during the acquisition two traces are recorded simultaneously: in one trace the even epochs are averaged, in the other – the odd ones (i.e. buffers A and B). To make sure, press the [Ctrl+E] key combination when the panel with the averaged traces is in focus (click on the panel with the left mouse button if necessary). This way you can switch the visibility between the summarized averaged trace and even/odd averaged traces (Fig. 4.7).

The response reproducibility can be inferred by even and odd trace shape. The data of even/odd traces are also used by statistic signal parameters (Fsp, SNR, RNL) for calculation.

In any case, if you are the least bit doubtful of the presence of response, record one more trace and watch whether the response is being reproduced. You can calculate correlation coefficient between the recorded traces and make other trace calculations using Trace|Calculation menu command.


82

For the manual arrangement of EP components, click the name of the corresponding component on the toolbar with the left mouse button (Fig. 8.4, a)) and move the ap-peared crosshair cursor to the point of the assumed component and click the left mouse button once again (Fig. 8.4, b). To cancel the component setting, click “Reset” button on the toolbar or press [Esc] button. The position of EP components can be corrected by dragging it with the mouse.

а) b)

Fig. 8.4. Manual marking of AEP components (peaks).

To mark EP components automatically use the menu commands Trace|Place EP components and Trace|Place all EP components. It is recommended to use the au-tomatic arrangement of EP components only for over-threshold stimulation.

To delete EP components use the menu commands Trace|Marker|Delete current ([Shift+Del]), Trace|Marker|Delete all on trace and Trace|Marker|Delete all.

After recording all the necessary traces you can start another technique (Test|New test or the corresponding button on the New test toolbar).

To preset a test template use Setup|Tests templates menu command.

AEP Tests

83

The general view of ABR test window is shown in Fig. 8.5.

Fig. 8.5. ABR test window

8.4.1. Statistic Signal Parameters

During the acquisition the values of statistic signal parameters are calculated. You can pay no attention to them and rely on automatic controls and default settings, but sometimes you may still need to understand their meanings.

Fsp – F-statistic for a Single Point, the statistic measure of signal-to-noise ratio. The more Fsp is the better as it raises the chances for response (EP) presence. By the mentioned F-statistic the dispersion analysis is meant. Value is proportional to aver-aged trace dispersion divided by dispersion of a single point (as a rule, the center of analysis epoch or approximate location of V peak is taken) over ensemble of traces (epochs). Using this value you can recognize when the averaging can be stopped (i.e., when either significant response is available or background electrical noise is ra-ther low to be sure in non-response). The optimal value was fitted by researchers em-pirically and equals to 3.1. If during the acquisition the Fsp value reaches 3.1, then the response different from noise is present in the recording with 99 percent probability. But it doesn’t mean that you should neglect visual trace analysis when you are making a final decision of response presence. It may happen that loud repetitive noise syn-chronized with stimulation frequency (muscle artifact or electrical artifact) will lead to more than 3.1 Fsp values while the genuine response (e.g., ABR response) is not present.

SNR – Signal-to-Noise Ratio. The more SNR is the better. The optimal value is 1.2.


84

RNL – Residual Noise Level (nV). The less RNL is the better. The optimal value is 90 nV.

8.4.2. Quick Analysis Windows

By default the analysis tables are located in the bottom part of the test window and the analysis graphs are positioned rightward (Fig. 8.5).

Analysis Tables

The tables of latencies, amplitudes and also EP aural asymmetry tables are available for all auditory EP (Table 8). The list of peaks displayed in them for the calculation of the latencies, intervals, amplitudes and amplitude ratios is set up in the test template settings (see chapter 7.2.4 “Markers”).

Table 8. Content of auditory EP analysis tables.

Column Name Content

N Trace name (number)

Stimulus Stimulus intensity (and scale)

<EP peak> (ms) EP peak latency

<Peak>-<Peak> (ms) Interval between EP peaks

<Peak>-<Peak> (µV) Amplitude of EP peak

<Peak>-<Peak>/<Peak>-<Peak> Amplitude ratio of EP peaks

Analysis Graphs

Among the auditory EP the analysis graphs are available only for ABR technique.

The graphs represent the latency-intensity function, showing the dependency of peaks latency (ms) on the stimulus intensity (dB). The data related to the right ear are drawn on the graph with the red circles, and the data related to the left one is with blue crosses. As a rule, the graphs are drawn for the main peaks: I, III and V.

Using the graphs you can visually compare the received data with the normative data. The norms depend on a patient age at the time of examination (that is why if the date of birth of a patient is not indicated in the patient card, the norms are not displayed). The norms are displayed on the graphs background as dark-grey areas. If the points of latency-intensity function are inside these areas, it means, that they are within the norm.

AEP Tests

85

8.5. Test Template Settings

As stated above you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”). In this section the specific parameters for AEP techniques (ABR technique is taken as an example) are described.

Fig. 8.6. ABR parameters

Parameter list:

“Don’t close acquisition window after stop” – if the check box is checked, the acquisi-tion window will not close after the auto stop (according to the statistic parameters or maximum stimuli count). It can be useful when you use the weighted averaging to move the slider on the histogram of the traces quality and impact the final averaging result before saving.

“Fsp threshold” is an auto-stop criterion. If the check box is checked and the Fsp val-ue exceeds this threshold during the acquisition, then the acquisition stops.

“SNR threshold” is an auto-stop criterion. If the check box is checked and the SNR value exceeds this threshold during the acquisition, then the acquisition stops.

“RNL threshold” is an auto-stop criterion. If the check box is checked and the RNL value becomes less than this threshold during the acquisition, then the acquisition stops.

“Sweeps amplitude threshold (µV)” is a threshold value to reject native traces with lar-ger amplitude during the acquisition. If you uncheck the checkbox, the traces rejection will be disabled and all native traces will participate in averaging.

Note: rejection by amplitude is available only if you use simple averaging algorithm (see “Av-eraging algorithm” below).

If several check boxes are checked, the acquisition stops automatically when the au-to-stop criteria for all the selected thresholds are being performed simultaneously.


86

“Averaging algorithm” – the selection of simple or weighted averaging. With simple averaging the traces are averaged with the same weight coefficients. It is often not op-timal and can result in the increase of test time. If you select the weighted averaging all the traces are included in the averaging, and different weight coefficients are ap-plied to them depending on their quality. The weighted averaging provides better re-sult (especially if noise is presented: muscle, electrical) and requires less number of stimuli, which shortens test time. This algorithm is used by default in ABR test.

ECochG Test

87

9. ECochG Test


Electrocochleography (ECochG) is a method to acquire auditory evoked potential re-sponses from cochlear and auditory nerves by providing sound stimulation to the pa-tient’s ear. The averaged acoustic nerve potential is called “action potential” (AP or I ABR peak). Cochlea response to stimulation is called “summating potential” (SP). AP and SP amplitudes and latencies are used to diagnose certain pathological conditions.

ECochG can be used to diagnose some vestibular and auditory conditions:

Meniere's disease (episodes of hearing loss, vertigo etc.).

Perilymphatic fistula.

ECochG simplifies the recognition of I ABR peak from patients with profound hear-ing loss. The fact is, it is impossible to recognize I ABR peak from such patients on standard ABR testing.

Using ECochG technique you can detect other conditions as well.


Getting ready for ECochG acquisition and placement of electrodes on a patient are quite similar to AEP technique.

As the AP and SP intensity is very low, surface electrodes are not suitable for this ap-plication. Special electrodes (tiptrodes, tympanic membrane, transtympanic electrode) must be applied for ECochG recording. Tiptrodes are the most commonly used elec-trodes. First, apply some conductive paste on the Tiptrodes and then insert them deeply into the ear canal carefully. These procedures must be carried out by experi-enced doctors only!

The electrodes are placed on a patient in the following way:

inverting (-): tiptrode is placed in the tested ear (it is connected to amplifier with special cable), then the sound tube of insert earphones is put in right there;

non-inverting (+): contralateral mastoid;

ground: forehead.


88

Placement of electrodes during single-channel recording is shown in Fig. 9.1.

Fig. 9.1. Placement of electrodes during single-channel recording for EcochG

While recording from both ears, a contralateral tiptrode in the ear canal may be used as the non-inverting (+) electrode.


The optimal parameter values for ECochG acquisition are shown in Table 9. To get more precise diagnosis it is recommended to record 3-4 traces with the same parame-ter values.

Table 9. Values of ECochG acquisition parameters

Stimulus: 100 µs click

Stimulation frequency: 10 Hz or 99.9 Hz. Use low stimulation frequencies for better AP recording and high stimulation frequencies for better SP recording.

Polarity: Rarefaction

Headphones: EAR-3A insert earphones

Intensity: 120 dB SPL

Filters: 10–3000 Hz

Analysis epoch: 5–10 ms


If excessive electrical noise line takes place during ECochG acquisition, you can switch on the adaptive notch filter.

ECochG Test

89


ECochG acquisition is quite similar to AEP acquisition (see the section 8.4 “Acquisition and Analysis”).

For ECochG acquisition three markers are used - Base, SP and AP which are placed automatically by default. You can also correct their positions by mouse drag or mark them manually like in AEP tests.

The general view of ECochG test window is shown in Fig. 9.2.

Fig. 9.2. ECochG test window


As stated above, you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”).

The parameters for ECochG technique are quite similar to the parameters for ABR technique (see the section 8.5. “Test Template Settings”).


90

10. TEOAE Test


Transient evoked otoacoustic emission (TEOAE) is an acoustic response generated by patient’s cochlea when provided with click or tone-burst stimulation. TEOAE is an indication of auditory receptor’s normal condition. It is extremely weak acoustic vibra-tions which can be recorded in external auditory canal by very sensitive low-noise mi-crophone. Emission is widely spread among persons with normal hearing (with audi-tory threshold of 25 dB HL or less). In particular, it is a measure of good hearing at medium frequencies.

TEOAE technique can be used to diagnose various auditory conditions in the follow-ing cases:

infant hearing screening;

monitoring of patients with a risk of hearing loss;

detection of cochlear dysfunction;

study of cochlear function and getting diagnosis before medical procedures;

detection of sensory hearing loss causes.

TEOAE appearance thresholds of persons with normal hearing are very close to be-havioral hearing thresholds. If patient suffers from sensory or conductive hearing loss, so that hearing thresholds are 30 dB or worse, emission disappears. That’s the dis-tinctive feature of TEOAE.

Transient evoked otoacoustic emission (TEOAE) can be successfully recorded at 3-4 days after birth. As TEOAE sensitivity is very high even to slight hearing impairment, this technique can be widely used in screening studies of infants.

TEOAE represents 2-3 (or rarely more) vibration groups of different frequencies ap-pearing in 6-8 ms after the stimulus beginning and lasting 20-30 ms.

After the acquisition you can get the result either in graphic or text form for further analysis.

TEOAE Test

91


A patient must be placed in a comfortable and quiet environment, preferably a sound booth where the patient lies down or sits comfortably. The patient should relax to re-duce noise level. To improve acquisition quality, it is recommended to inspect pa-tient's ear canal. Cleaning of the ear canal shall only be performed by a person trained in such procedure in order to prevent any irreversible middle ear damage.

Please pay attention to the OAE probe version and its sensitivity. The sensitivity (mV/Pa) and the version number are usually indicated on OAE probe’s label. Before the first use of the program to record OAE, please make sure that correct OAE probe version and sensitivity value are set in the program settings (see chapter 7.1.3 ““Hardware” Page”).

10.2.1. OAE Probe Fitting

The important stage of otoacoustic emission test is the correct placement (fitting) of a probe to the external ear canal of a patient.

Before inserting OAE probe into a patient’s ear canal, make sure OAE probe tip is placed correctly.

For good fitting the OAE probe should comply with the following requirements:

1. It obturates the external ear canal to convert the small oscillations of the tympanic membrane to the pressure fluctuations which can be detected with use of the probe microphone.

2. It prevents contamination of the record with external noise.

3. It provides the required acoustic environment for the generation of the correct stimuli by the probe telephone.

To comply with the aforementioned requirements, the OAE probe should be inserted together with the soft replaceable ear tip. The ear tip size is selected after the visual assessment of a patient’s external ear canal size. The delivery set of Neuro-Audio digital system includes cone-shaped and mushroom-shaped ear tips. These ear tips are disposable and should be thrown away after use.

The cone-shaped ear tips are inserted deeper down into the ear canal than the mush-room-shaped ones. Deeper insertion into the ear canal allows for the measurement of larger emissions due to the reduced ear canal volume.

When applying the mushroom-shaped ear tip, please make sure that the ear tip is fully inserted into the ear canal, not leaving the ear canal open.

If the ear tip is too small, it can let the noise in the external ear canal or distort the stimulus. If the ear tip is too large, it can’t be inserted to the external ear canal deep


92

enough. This can lead to the decrease of response amplitude and probe instability during the test. Besides, if the ear tip is large, it is impossible to exclude the consider-able noise interference.

Ear tip should be placed on OAE probe completely.

If the ear tip ends in horn widening of a hole, it should be placed on a probe com-pletely so that the horn beginning should be located on the same level with acoustic lines holes. If the ear tip does not end in the horn widening, it should be placed on a probe so that it cut should be located on the same level with acoustic lines holes (Fig. 10.1). The ear tips sticking out the acoustic lines can cause additional fluctuation of the stimulus.

Fig. 10.1. Ear tip placement on the probe.

The removal of the ear tip is performed in the following way. Holding the nozzle latch-es of OAE probe, slide the ear tip off according to Fig. 10.2.

Fig. 10.2. Correct removal of ear tip.

To avoid breaking the latches, hold the OAE probe for the latches. Other fingers positions during the ear tip removal are not recommended!

TEOAE Test

93

Fig. 10.3. Incorrect removal of ear tip.

When the probe is inserted into ear canal, its tip should not be set against the wall of the external ear canal, because it interferes with the stimulus presentation and/or OAE acquisition. Such situation can be easily detected by watching the stimulus trace shape on the stimulus panel.

The Fig. 10.4 a) represents the oscillating stimulus waveform. It is not adequate for TEOAE registration. In the ear of an adult it can occur due to bad fitting of OAE probe or the atypical form of the external ear canal. In the last case the stimulus waveform should be accepted, however, always try to re-insert the OAE probe again. The Fig. 10.4 b) represents the stimulus waveform at the correct fitting of OAE probe for adults. As for the newborns, the additional fluctuations of stimulus can always be de-tected. The Fig. 10.4 c) shows the acceptable level of fluctuations of the newborn.

а) b) c)

Fig. 10.4. The stimulus waveform (1).


94

The Fig. 10.5 a) demonstrates the effect of the excessive proximity of the OAE probe to the wall of the external ear canal or other barrier. The slow round low-frequency wave following the initial sharp peaks is characteristic for this condition. In this case the OAE probe should be re-inserted. The Fig. 10.5 b) shows the impact of the exces-sive noise for the stimulus waveform. The cause can be in overly loose OAE probe in-stallation allowing the penetration of the external noise to the external ear canal, or noises emitted by the patient. The typical sounds emitted by the patient include breathing, swallowing or tooth-grinding.

a) b)

Fig. 10.5. The stimulus waveform (2)

10.2.2. Newborn Hearing Screening

To perform a newborn hearing screening, select “TEOAE (screening)” test template.

The newborn should stay quiet and calm, it is usually preferred for the infant to be asleep. To calm a baby down, you can use a baby's dummy, however, the sucking causes the additional noise and decreases the probability of test passing.

It was already mentioned that it is preferable to use cone-shaped ear tips which can be inserted deeper down into the ear canal. However, the deep insertion of a probe can wake up a newborn and make her/him nervous. In this case it is more reasonable to use mushroom-shaped ear tips.

Warming the ear tips prior to insertion helps to keep the baby calm.

The external ear canal of the newborns can collapse during the OAE probe insertion. To prevent it, draw the lobe of the auricle back and down very carefully to level the ear canal (Fig. 10.6). Inspect the external ear canal to make sure that it is opened. Care-fully insert the OAE probe into the newborn’s ear with the gentle rotational move-ments. Make sure the OAE probe is inserted at the proper angle. The general rule is the OAE probe must be directed to the newborn’s nose (Fig. 10.7). After that, leave the auricle.

A newborn can start playing/stirring, displacing the OAE probe in the ear canal. It is a normal behavior.

TEOAE Test

95

Wait for a newborn to calm down, and then run the test.

Fig. 10.6. OAE probe fitting.

Fig. 10.7. OAE probe position in a newborn’s ear.

The ears of the newborns are often wet or contain the extraneous masses. If the good stimulation was not obtained at the first insertion of a probe, replace the ear tip with these extraneous masses by the new one and try again.


96


The recommended parameter values for TEOAE acquisition are shown in Table 10.

Table 10. Values of TEOAE acquisition parameters

Stimulus: 0–50–300 µs trapezoid; 100 µs click

Stimulation frequency: 49 Hz (66 Hz for newborns)

Intensity: 75 dB (80 dB for newborns)


Number of stimuli: 250–500 (1000 for newborns)

Analysis epoch: 20 ms (15 ms for newborns)

Noise level: 50 dB SPL

Pass criterion: 3 from 5 frequencies, 6 dB signal/noise, 70% reproducibility (for newborns: 3 of 5 frequencies, 4 dB signal/noise)

TEOAE Test

97


Start acquisition with repetitive stimulation using Acquisition|Repetitive stimulation ([Ctrl+R]) menu command and follow the process of signal averaging. To cancel the acquisition use Acquisition|Cancel ([Esc]) menu command. To stop the stimulation for some time use Acquisition|Pause [space key] menu command. The acquisition window is represented in Fig. 10.8.

Fig. 10.8. TEOAE acquisition window.

The top part of the acquisition window contains the standard averaging information panel. The number of averaged and rejected traces and also the current stage of TEOAE acquisition are displayed on it.

The “Averaging” tab displays parameters of the stimulus (recorded via the OAE probe microphone) and response, including the trace shape and spectrum.

Stages of TEOAE Acquisition:

probe fitting check;

stimulus calibration;

acquisition itself.

Averaging information panel Table of OAE presence by frequencies

TEAOE spectrum (signal and noise)

TEAOE trace (A and B buffer)

Stimulus spectrum

Stimulus waveform

Stimulus stability and volume

Noise level, response reproducibility

Levels of averaged response and residual noise


98

Probe fitting check is an objective test of correctness of probe fitting in external ear canal. It is done by analyzing the stimulus, recorded via probe’s microphone.

The acquisition window during this stage displays two linear scales: the one is display-ing the acoustic meatus volume (“volume” indicator appears instead of reproducibility scale), and the other one is displaying the noise level (“noise” indicator). If the noise level or the volume exceeds its respective threshold, the corresponding scale be-comes red, and if it does not, it stays green. If it is too noisy in the room, the accept-able noise level can be increased by dragging the scale slider with the mouse. When the OAE probe is fitted correctly, both scales should be in the green area. If after a short check the software detects that the OAE probe is fitted incorrectly, the stimula-tion will pause and the message “Check probe fitting” will appear instead of current acquisition stage. In this case it is required to re-insert the probe and use Acquisition|Pause ([Space]) menu command to restart the stimulation.

Note: passing the probe fitting check does not guarantee its correct fitting, because the device can not detect the situation when the probe tip is fit against the wall of the ear canal, or when the canal is obscured, for example, by the cerumen.

If the software detects that the OAE probe is fitted correctly, it will switch to the next stage: stimulus calibration.

Stimulus calibration is required for the accurate setting of the specified stimulus in-tensity using the OAE probe’s built-in microphone. The acquisition window always displays the specified and achieved levels of stimulus intensity (in dB SPL).

TEOAE acquisition is carried out in nonlinear mode. The sets of 4 stimuli are used in strict sequence – one large stimulus and three small ones.

During the acquisition the following information is displayed:

Number of averaged and rejected traces (artifacts). Large number of artifacts indi-cates either strong external acoustic noise or bad OAE probe fitting. In this case the test should be repeated in more quiet conditions or after re-inserting the probe.

Stimulus stability. The ideal variant is when it is equal to ”1”. The stability less than 0.9 indicates that the probe had been considerably changing its position during the acquisition process. If OAE was not detected in this case, i.e. the “REFER” result was displayed after the test termination, repeat the test after re-inserting the probe; make sure that the probe’s position is stable this time.

The level of the averaged response, in dB SPL is opposite the “A&B” label. It is the reference information, providing some indication of the total OAE response ampli-tude, but it is only valid in case the A&B value exceeds the total level of А-В noise.

Total residual noise level, in dB SPL is opposite the “A-B” label. The residual noise level decreases in the process of the averaging. If OAE is not detected (i.e. the pro-gram has come up with “REFER” result), and the residual noise level exceeds 10 dB, it indicates the excessive level of external acoustic noise and means that the test should be repeated in more quiet conditions or after the re-inserting probe.

TEOAE Test

99

“Reproducibility, %”. This value is the correlation between odd and even traces of a signal.

The table of OAE presence by frequencies. The top row, marked as “kHz”, contains 1, 2, 3, 4 and 5 kHz frequencies. The middle row, marked as “SNR”, displays the current signal-to-noise ratio on the given frequency (in dB), calculated with the use of the digital bandpass filter. The OAE presence on the given frequency is marked

by “ ”symbol. The criterion of its presence is specified in TEOAE settings (by de-fault, 6 dB is for adults and 4 dB – for newborns).

By default, the acquisition will stop automatically after a while and the averaged trace will be saved. The stop of acquisition depends on several parameters in test template settings. Firstly, the automatic stop must be switched on (otherwise, you can stop av-eraging only manually using Acquisition|Stop menu command). Secondly, the aver-aging will last at least minimum number of epochs specified in a template. Thirdly, if the averaging lasts up to the maximum number of epochs specified in a template, it stops immediately.

In fact, during the acquisition two traces are recorded simultaneously: in one trace the even epochs are averaged, in the other – the odd ones (i.e. buffers A and B corre-spondingly). To make sure, press [Ctrl+E] key combination when the panel with the averaged traces is in focus (click on the panel with the left mouse button if necessary). This way you can switch the visibility between the summarized averaged trace and even/odd averaged traces. High correlation between A and B traces indicates OAE presence, and the subtracted trace (A-B) helps to calculate the residual noise level. The response spectrum has two areas: the dark one shows the noise level and the light one indicates the response level, in those areas where it exceeds the noise level.


100

The general view of TEOAE test window is shown in Fig. 10.1.

Fig. 10.1. TEOAE test window


As stated above, you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”). In this section the specific parameters for TEOAE technique are described.

Fig. 10.2. TEOAE parameters

DPOAE Test

101

“Noise level (dB SPL)” means a threshold value to eliminate epochs by noise level during the acquisition.

“Use window function”. If this checkbox is checked, signal smoothing in the analysis epoch’s beginning and end (by 10% of total duration) takes place before filtration. This serves to better prepare the signal to the application of the discrete Fourier transform.

“PASS/REFER criteria” work in the following way: if OAE is detected at specified Fre-quencies count as minimum, with preset Signal/noise ratio, and the signal Reproduci-bility shows the specified percent as minimum (if the check box is checked), as well as OAE level is no less than preset value in decibels (if the check box is checked), then the test result is “Pass”. Otherwise, the test result is “Refer”.

If all the criteria are performed during the acquisition, the auto-stop takes place, in case it is switched on in the common parameters.

11. DPOAE Test


Distortion product otoacoustic emission (DPOAE) is an acoustic response generated by patient’s cochlea when provided with two-tone stimulation. As well as TEOAE, DPOAE represents extremely weak acoustic vibrations which can be recorded in ex-ternal auditory canal by very sensitive low-noise microphone. As a rule, DPOAE is de-tected in persons with normal hearing only.

The technique is rooted in spectrum analysis of activity recorded in response to simul-taneous stimulation by two tones - F1 and F2. F2 is a primary tone and F1 is a secon-dary one.

During DPOAE acquisition the dependence of OAE intensity on stimulation frequency (F2) is plotted on DP-gram. Noise level on each frequency is plotted on the graph as well. The received information gives a true functional status of outer hair cells from the base of cochlea up to its apex, but it cannot be called an “audiogram”.


For DPOAE acquisition a special OAE probe is used. This probe has built-in miniature speakers and a microphone, which should be inserted into the external auditory canal of a patient.

To get your patient ready for DPOAE acquisition, see the recommendations for TEOAE technique (the section 10.2. “Getting Ready for Acquisition”) as the prepara-tions are quite similar.


102


The recommended parameter values for DPOAE acquisition are shown in Table 11.

Table 11. Values of DPOAE acquisition parameters

Stimulus intensities: 55 dB SPL primary stimulus (F2); 65 dB SPL secondary stimulus (F1)


Points per octave: 2-3 (2 for screening)

Pass criteria: 70% frequencies; 6 dB signal/noise


During DPOAE acquisition two continuous tones (F1 and F2) are used as stimuli. Pri-mary tone frequency is always preset. And secondary tone frequency (F1) is calcu-lated by the following ratio: F2/F1 = 1.22.

Set the required initial values of stimulus parameters in the test template dialog box (in the “Stimulator” page of the “Hardware” page).

Start acquisition with repetitive stimulation using Acquisition|Repetitive stimulation ([Ctrl+R]) menu command and follow the process of signal averaging. To cancel the acquisition use Acquisition|Cancel ([Esc]) menu command. To stop the stimulation for some time use Acquisition|Pause [space key] menu command.

In DPOAE tests the acquisition is divided into several stages:

probe fitting check and frequency response measurement for each probe speaker;

stimulus calibration (in tone mode, F2 frequency is 2 kHz);

DPOAE acquisition.

Probe fitting check is an objective test of correctness of probe fitting in external ear canal. It is done by analyzing the stimulus, recorded via probe’s microphone. You will not be able to start acquisition if this check doesn’t pass. At this step the broadband acoustic clicks are used as stimuli.

Stimulus calibration is applied for precise setting of specified stimulus intensity by using the OAE probe’s built-in microphone. As well as during DPOAE acquisition, two continuous tones of different frequencies (F1 and F2) are used as stimuli at this step. The actual intensity of each tone (in decibels) in ear canal is determined by response spectrum. Then the intensity of each tone is corrected and applied to device, until the actual tone intensities reach the preset values specified in the test settings.

During the acquisition at one frequency the responses are averaged and the signal and noise values in decibels are calculated by response spectrum. Distortion product level in decibels is calculated by response spectrum as well. The frequency of distor-tion product (DP), where the maximum response intensity (distortion product) is ob-

DPOAE Test

103

served, is usually calculated by the following formula: DP = 2*F1 – F2. You can also set some other standard formulas in the test template settings, but this formula is used most often, as its amplitude should be maximal.

After you get the stable values of signal and noise at one frequency, the automatic switch to the next frequency takes place. Number of acquisition points (frequencies being tested) per octave is set in the test template settings. And every time the inten-sities applied to the device are corrected using the measured frequency response characteristics for each speaker of the probe.

When the full DP-gram is plotted, the acquisition stops automatically and the DP-gram is saved for analysis.

The general view of DPOAE test window is shown Fig. 11.1 and acquisition window is given in Fig. 11.2.

Fig. 11.1. DPOAE test window


104

Fig. 11.2. DPOAE acquisition window.


As stated above, you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”). In this section the specific parameters for DPOAE technique are described.

Fig. 11.3. DPOAE parameters

ASSR Test

105

“Points per octave” means the number of frequencies under study within one octave during the acquisition.

“Distortion product frequency” is the formula to calculate DP frequency.

“Noise level (dB SPL)” means a threshold value to eliminate epochs by noise level during the acquisition.

“Max point time (s)” is the limitation of acquisition duration at one frequency. If OAE is not selected for a long time, the switch to the next frequency takes place after the pre-scribed time.

“PASS/REFER criteria” work in the following way: if OAE is detected at specified Fre-quencies count as minimum (percentage of total count), with preset Signal/noise ratio, and the OAE level equals to the preset value in decibels (if the check box is checked), then the test result is “Pass”. Otherwise, the test result is “Refer”.

If all the criteria are performed during the acquisition, the auto-stop takes place, in case it is switched on in the common parameters.

12. ASSR Test


Auditory steady-state response (ASSR) is used to make an objective estimation of auditory thresholds. An estimated audiogram is the final result of ASSR test. Using this technique you can get the threshold values equal to behavioral ones with the ac-curacy of 10-15 dB.

ASSR appears in the auditory nerve and brainstem in response to the repetitive acoustic stimulation. The sequence of stimuli following each other evokes the series of auditory evoked potential responses that overlap due to the high stimulation fre-quency. This steady state response is ASSR.

The main clinical application of ASSR is for detailed frequency-specific hearing as-sessment in babies who are referred for follow-up testing from a universal newborn hearing screening program. The estimated ASSR audiograms provide a basis for de-termining the most appropriate intervention, e.g., recommendation for a hearing aid or consideration for a cochlear implant.

The ASSR has the following advantages over ABR technique:

frequency-specific signal is used as a stimulus which is more similar to pure tone signal than the stimuli used in ABR technique;

stimulation intensity is up to 120 dB HL which is useful for assessment of severe hearing loss in infants and young children;


106

automated response detection and analysis.

The spectral analysis and methods of statistical analysis of circular data are used for ASSR analysis. Visual analysis of traces (like in ABR tests) is not required.

However, in spite of all advantages, many audiologists still recommend to use ASSR only together with the tone ABR.

If during ASSR test the elevation of hearing threshold is detected (even if on one frequency), it is required to perform tone-burst ABR (air and bone sound conduction)!

12.1.1. Stimulus Characteristic

Stimulus in ASSR is the constant tone (typically of standard audiometric frequency) amplitude-modulated (AM) or frequency-modulated (FM). As a rule, the tone is used together with the amplitude and frequency modulation (AM+FM). The stimulus exam-ple is given on the Fig. 12.1.

Fig. 12.1. ASSR stimulus example: tone with 1000 Hz frequency, 100 Hz amplitude modulation fre-quency.

The amplitude of the tone goes from 0 to 100% one hundred times per second. The resulting stimulus can be thought of as a continuous series of tone-bursts with no in-ter-stimulus interval. In this example, the tone-burst is repeated every 10 ms.

ASSR Test

107

The frequency spectrum of such stimulus is represented in Fig. 12.2. It is seen that the main peak of the stimulus energy is present at 1000 Hz frequency (carrier fre-quency), secondary peaks are at 900 and 1100 Hz (i.e. at ±10% from 1000 Hz). In the given example the stimulus energy is presented only in this narrow range.

Fig. 12.2. ASSR stimulus spectrum (tone — 1000 Hz, amplitude modulation — 100 Hz).

ASSR stimulus is optimized for the frequency specificity and is closer to the pure tone than clicks and short tone-bursts used in ABR.

12.1.2. Response Characteristic

When an ASSR stimulus is presented above threshold, EEG activity is synchronized with the amplitude-modulation frequency (in the example described beforehand – 100 Hz). This EEG activity synchronized with modulation frequency is the basis of ASSR response. The ASSR response is the stable (steady-state) sequence of overlapped auditory EP responses to the sequence of stimuli (tone bursts) following each other continuously (Fig. 12.10).

Fig. 12.3. ASSR response.


108


A patient should relax lying on bed comfortably in a quiet room. It is desirable that the room is soundproof. It is recommended to test the infants and newborns while they are sleeping (to reduce the level of background EEG activity). Adults can be examined in wakeful state. It is recommended to use insert earphones, for example EAR-3A (TIP-300).

Use low-noise computers. If the computer emits great acoustic noise, the hearing thresholds for low frequencies (1000 Hz and lower) can be identi-fied incorrectly (they will be overestimated).

The montage of electrodes for ASSR acquisition is similar to AEP acquisition (see the section 8.2. “Getting Ready for Acquisition”). By default, the two-channel montage is used and the ipsilateral trace is analyzed during the acquisition.


The recommended parameter values for ASSR acquisition are shown in Table 12.

Table 12. Values of ASSR acquisition parameters

Stimulus: Tone (250 Hz – 4 kHz), 100% amplitude modulated and 10% frequency modulated, modulation frequency – 46 Hz (for adults) or 81 Hz (for children and adults asleep)

Intensity: 50 dB HL starting point, then move up/down to estimate a threshold at certain tone frequency (max: 120 dB HL)

Analysis epoch: 1 s

Number of averaging in group: 2–4

If excessive electrical line noise takes place during ASSR acquisition, you can switch on the adaptive notch filter.


For ASSR acquisition, after a new exam creation in the “New test” window, select the “Auditory Steady-State Response (ASSR)” technique in the list of techniques and the corresponding template from the test templates list (in addition to main template three more templates are available by default: for children younger 10 years asleep, for adults and children older 10 years asleep and also for awaken adults and children older 10 years).


ASSR Test

109

Connect the headphones to the amplifier unit. Set the required initial values of stimu-lus parameters on the “Information” panel. Start acquisition with repetitive stimulation using Acquisition|Repetitive stimulation ([Ctrl+R]) menu command.

The modulation frequency is selected initially together with the test template and it is usually not changed during the test. The modulation frequency depends on patient’s age. Standard test templates are enough in most cases.

12.4.1. ASSR Analysis

One of the main advantages of ASSR technique in comparison with common AEP is the response analysis technique. Unlike the AEP, there is no need to analyze the trace visually, identify the peaks and also measure their latency and amplitude.

The detection of the ASSR is done using computer algorithms which are applied to the recorded EEG signal to analyze the amplitude and phase of EEG activity corre-sponding to the modulation frequency of the tone, and to determine the presence or absence of an ASSR. The objective analysis techniques increase its quality and elimi-nate the “human factor”.

ASSR analysis consists of the two main steps:

1. EEG samples (epochs) are recorded and analyzed during the stimulation. Up to 64 epochs can be analyzed per one trial. Trial is the combination of the tone fre-quency and the stimulus intensity (for example, 1000 Hz at 30 dB HL volume).

2. In each epoch, EEG amplitude and phase corresponding to the modulation fre-quency are determined. Each epoch is displayed as vector in the polar graph. Vector length corresponds to EEG amplitude and vector angle corresponds to phase (delay) between the modulated tone and brain response.

The set of vectors confirming the ASSR response is represented on the Fig. 12.4. The vectors are grouped together (“clustered”) on the polar graph indicating there is “phase-locked” brain response; the EEG samples are synchronized with the tone modulation frequency. It means that both ear and brain respond to the tone.


110

The vectors received when the tone is presented at a sub-threshold or inaudible level are represented on the same figure rightward. The vectors vary in length (i.e., ampli-tude), but more importantly, the phases are randomly distributed around the polar plot. It means that there is no phase synchronization between EEG and modulated tone, the EEG is “random”, and ASSR response is not detected.

Fig. 12.4. Examples of possible vectors distribution at acquisition of ASSR trial.

12.4.2. Objective Response Identification

The determination of “phase-locked” versus “random” response is not based on visual interpretation of the graphic plots, but rather on the basis of statistical analysis com-pleted in the real-time during the recording. P-value is calculated, it is considered to be the probability that the given distribution of vectors is achieved only due to noise alone. Correspondingly, the inverse value (1-P) indicates the probability that the dis-tribution of vectors is obtained because of the “phase-locked” brain response (statisti-cally significant response).

The analysis algorithm will automatically stop the stimulation and data acquisition when the specified probability value will be achieved. It shortens the exam time. Also the algorithm will automatically stop the recording after the analysis of 64 EEG epochs or in case it is impossible to achieve the statistically significant value of the probability after 64 epochs. The epochs with too big amplitude are marked as “noise” and are not included in the analysis.

ASSR Test

111

The P-value is calculated on the basis of phase values of each epoch. On the prob-ability graph (Fig. 12.5) the change of inverse value (1-P) over time is depicted. This is the probability that we have the statistically significant response.

Fig. 12.5. The graph of probability change in time for one ASSR trial.

When the graph of response probability crosses the line 97%, it means that the phas-es of the vectors have the statistically significant distribution synchronized by phase. The probability threshold P < 3% means that the probability of the false-positive result for ASSR is only 3%. Correspondingly, the phases synchronization with 97% probabil-ity means that the brain response is available.

At the end of each trial the result is displayed: “Phase-Locked” (the synchronization of phases meaning a brain response is present) or “Random” (no response).

The trials are marked on the grid looking like the audiogram (Fig. 12.6). The trial with “phase-locked” result is indicated by the arrow directed upward, that means that ASSR threshold level is less than the current stimulus level. Correspondingly, the “random” trial is indicated by arrow directed downward, i.e. threshold is supposed to be on higher stimulus intensity level.

Fig. 12.6. The representation of all recorded ASSR trials for the right ear.


112

The ASSR trials on one frequency should continue until the threshold is determined, i.e. the lowest level of stimulus intensity, on which the response is present. The thresholds are identified for all available audiometric frequencies.

12.4.3. Audiogram Estimation

The ASSR thresholds are used to estimate the pure-tone audiogram. The estimation utilizes an algorithm based on published research from the University of Melbourne in which ASSR thresholds measured for patients with various amounts of hearing loss were correlated with their behavioral audiograms. This research determined that the ASSR thresholds have a high correlation with pure tone thresholds, and this correla-tion is highest (more than 95%) for those with moderate, severe and profound hearing loss.

The ASSR thresholds show less than a 10 dB difference compared to pure tone thresholds for those with moderate and severe losses, and are generally within 20 dB of pure tone threshold for normal hearing and mild losses.

The estimated audiograms on the basis of ASSR thresholds are given on the Fig. 12.7.

a) b)

Fig. 12.7. Examples of estimated audiograms: a) normal hearing; b) hearing loss.

The accuracy of the estimated audiogram visualization is displayed by the calculated error values (vertical lines in each examined point of audiogram – “brackets”). Error means a two-sided standard deviation from the estimated threshold value. The accu-racy decreases (wider brackets) when patient’s hearing ability is near normal. But if a patient suffers from serious hearing impairment and the auditory thresholds are nota-bly higher than normal ones, the error will decrease up to 5 dB only (narrow brackets). It means that the accuracy of estimated audiogram is higher at the very moment it is needed most of all – when the most suitable hearing aid is being selected for a pa-tient.

ASSR Test

113

The general view of ASSR test window with all the trials (one trial is shown in details) is shown in Fig. 12.8. You can select trials with the mouse. In the left bottom corner of the window a graph of all vectors of a current trial is displayed. In the right bottom cor-ner of the window its probability view is displayed.

Fig. 12.8. ASSR test window

The general view of estimated audiogram (the “Audiogram” page) is shown in Fig. 12.10.

Fig. 12.9. ASSR estimated audiogram


114


As stated above, you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”). In this section the specific parameters for ASSR technique are de-scribed.

Fig. 12.10. ASSR parameters

“Number of epochs to average”. This parameter is used to specify the number of na-tive traces averaged in one to calculate one vector on a vector graph during ASSR acquisition. The more native traces are averaged the better is the response, but at the same time the acquisition lasts for a longer time.

“Audiogram calculation”. Choose a formula for estimated audiogram calculation. There are two formulas: for adults (and for children older than 10 years) and for chil-dren younger than 10 years.

Multi-ASSR Test

115

13. Multi-ASSR Test

13.1. Brief Description

Multiple-frequency auditory steady-state response (Multi-ASSR) technique is used to perform objective frequency-specific hearing assessment. The end result of a test is an estimated audiogram. Using this technique you can get the threshold values equal to behavioral ones with the accuracy of 10-15 dB.

The theoretical basis of this technique was developed in Canada (Dr. Terry Picton and others) and described in many articles in peer-reviewed scientific journals.

This technique is a further development of ASSR technique (see chapter 12 “ASSR Test”) and is intended to minimize the exam time due to simultaneous testing of both ears at four main audiologic frequencies (50, 1000, 2000 and 4000 Hz).

Because of hardware constraints multi-ASSR technique can be performed only on Neuro-Audio (2010 version) device.

13.1.1. Stimulus Characteristic

The stimulus in multi-ASSR is binaural, it is delivered to both ears simultaneously.

Resulting stimulus for each ear consists of a sum of four stimuli.

Each separate stimulus is a continuous tone (of standard audiologic frequency), am-plitude-modulated (AM) or frequency-modulated (FM) one. As a rule, both amplitude and frequency modulation are used (AM + FM).

Each separate stimulus has its unique modulation frequency. It allows to independ-ently detect the response to each stimulus during the stimulation. These modulation frequencies are preset in the program and are adjusted in a way to provide accurate synchronization between the stimulator and the amplifier during the acquisition.

The independent volume control of each stimulus and also some stimuli switch on/off are possible.

Besides, a user can set (in stimulator settings) the range of used modulation frequen-cies – 40 Hz and 90 Hz modes:

90 Hz mode (by default): is applied for sleeping infants and adults. The response amplitudes are not very high, however the response does not depend on the pa-tient’s awake state.

40 Hz mode: is applied to adults being awake. The amplitude response is consid-erably higher, however the response depends on the patient’s awake state.


116

13.1.2. Response Characteristic

In ASSR when suprathreshold stimulus is delivered to an ear, EEG activity is syn-chronized with modulation frequency. In multi-ASSR the same happens with the re-sponse to each separate stimulus. Thus, if a patient hears a stimulus, a frequency spectrum (FFT) will have a peak emerging above the noise floor exactly at the modu-lation frequency of this stimulus.

Since each individual stimulus has its own modulation frequency, responses to them can be differentiated on the frequency spectrum (FFT).

The stimulus and the response for multi-ASSR are shown in Fig. 13.1. The modulation frequencies shown in this figure are given as example and differ from the actually used ones.

13.2. Getting Ready to Acquisition

A patient should relax lying on bed comfortably in a quiet room. It is desirable that the room is soundproof. It is recommended to test the children and newborns while they are sleeping (to reduce the level of background EEG activity). Adults can be examined in a wakeful state. It is recommended to use insert earphones, for example EAR-3A.

Use low-noise computers. If the computer emits great acoustic noise, ASSR hearing thresholds for low frequencies (1000 Hz and lower) can be detected incorrectly (they will be overestimated).

The montage of electrodes for multi-ASSR acquisition is similar to that used for ABR acquisition (see the section 8.2. “Getting Ready for Acquisition”). By default, the two-channel montage is used.

Multi-ASSR Test

117

Fig. 13.1. Stimulus and response in multi-ASSR technique.


In most cases the default settings should not be changed.

If excessive electrical line noise takes place during multi-ASSR acquisition, you can switch on the adaptive notch filter.


For multi-ASSR acquisition, after a new exam creation in the “New test” window, se-lect the “Multi-ASSR” technique in the list of techniques and press the “OK” button.



118

Connect the headphones to the amplifier unit. Set the required initial values of stimu-lus parameters on “Information” panel and in test template settings. Start acquisition with repetitive stimulation using Acquisition|Repetitive stimulation ([Ctrl+R]) menu command.

The view of multi-ASSR test window during the acquisition is shown in Fig. 13.2.

On the information panel you can check (turn on/off) the stimulation frequencies (sep-arately for each ear) you are interested in.

The graphs of response probability occupy the main part of the main window.

Fig. 13.2. Multi-ASSR acquisition window.

Multi-ASSR Test

119

13.4.1. Acquisition Sequence

After acquisition start a user should monitor the process and if it is necessary interfere in it in the following way:

“Pass” result at one frequency (green response probability graph) – lower stimulus intensity should be selected for this frequency in the context menu.

“Refer” result at one frequency (red response probability graph) – higher stimulus intensity should be selected for this frequency in the context menu.

The purpose is to detect the hearing threshold for each frequency and each ear, i.e. the minimal intensity with “Pass” result. After the exam finishing, stop the acquisition.

After that switch to the “Audiogram” tab where the program will automatically calculate the audiogram on the basis of detected multi-ASSR thresholds. This audiogram is in-cluded in the report.

13.4.2. Multi-ASSR Analysis

As in ASSR, in multi-ASSR the response detection is done using computer algorithms which are applied to recorded EEG. The objective analysis techniques increase its quality and eliminate the “human factor”.

Since ASSR response level is rather small compared with the amplitude of back-ground EEG activity, it is necessary to take measures to decrease the noise level.

Improving the signal-to-noise ratio

As in other evoked potential applications, ASSRs are recorded in conjunction with other EEG activity or ‘noise’ and SNR is an important aspect. The SNR can be im-proved with similar efficiency by either averaging the data in the time domain or using the data to increase the duration of the sweep which will be submitted to FFT analy-sis. Averaging together repeated recordings reduces the level of activity in the re-cording that is not time-locked to the stimuli. Increasing the duration of the activity submitted to the FFT increases the frequency resolution of the analysis. Provided the stimulus frequencies are precisely locked to the recording frequencies, increasing the sweep duration thus reduces the noise level, by distributing the power across more FFT bins, without affecting the amplitude of the response, which is represented within a single FFT bin.

To detect the response presence, Fisher's Exact Probability Test is used (F-test).


120

13.4.3. Objective Response Identification

During the acquisition process the response probability graph is plotted for each fre-quency and each ear.

Fig. 13.3. Graph of probability change in time for right ear at 2000 Hz frequency.

Each graph has the label with the corresponding stimulus intensity.

When probability achieves 95%, the acquisition and the stimulation on the specified frequency and for the specified ear are stopped and the probability graph turns green.

If the response is not detected during the specified time, the acquisition and the stimu-lation on this frequency and for this ear are stopped and the probability graph turns red.

Two numbers: response amplitude (A) and residual noise (RN) in nV are displayed in the bottom part of each probability graph.

It is recommended to continue acquisition until the noise level (RN) lowers to 10 nV. To achieve this, it may be necessary to increase the maximum test time using the context menu.

13.4.4. Audiogram Calculation

Multi-ASSR thresholds are used to estimate the audiogram. The estimation utilizes an algorithm based on the research of Canadian group of scientists headed by Dr. Terry Picton in which multi-ASSR thresholds measured for patients with various amounts of hearing loss were correlated with their behavioral audiograms. This research deter-mined that multi-ASSR thresholds have a high correlation with audiogram thresholds, and this correlation is highest (more than 95%) for those with severe and profound hearing loss.

The audiogram calculated by the program is displayed on “Audiogram” tab of main test window. The multi-ASSR thresholds which are currently detected are visualized on the same tab. During the acquisition you can easily switch between “Audiogram” and “ASSR” tabs.

Multi-ASSR Test

121

The example of estimated audiograms is given in Fig. 13.4.

Fig. 13.4. Estimated audiograms for multi-ASSR.

The view of multi-ASSR test window is given in Fig. 13.5.

Fig. 13.5. Multi-ASSR test window.


122


As it was stated above, you can find the specific parameters for each particular tech-nique on the “Parameters” page of the test template dialog box (see the chapter 7.2. “Test Template Setup”). In this chapter the specific parameters for multi-ASSR tech-nique are described.

Fig. 13.6. Multi-ASSR parameters.

“Initial Level (dB)” parameter specifies the initial level of stimulus intensity for right and left ears separately.

“Test frequencies (Hz)” parameter allows selecting which carrier frequencies to use for the stimulus. If the frequency checkbox is checked, it will be included to the result-ing stimulus.

Besides, you can set extra parameters on “Hardware” page of the test template set-tings dialog box by selecting “Stimulator” tab. On this tab you can choose the required stimulus intensity scale (SPL or HL) and set up the stimulus modulation parameters (amplitude and frequency modulation percent, modulation frequency range: 40 Hz and 90 Hz modes).

Cognitive EP Tests

123

14. Cognitive EP Tests


Unlike EP, main contribution to which is the physical impact of the stimulus, the cogni-tive EP are formed by the brain activity emerging either spontaneously in connection with volitional (or arbitrary) acts of a patient, or in connection with the presented stimu-lus, independent from its physical parameters, but due to its meaning.

Among cognitive EP, P300 (by latency period in milliseconds) positive polarity poten-tial has rather wide clinical application. It emerges when a person attracts special at-tention to the stimulus. This type of testing may provide the physician with very useful information about pathologies of higher nervous activity. P300 changes characteristi-cally in case of psychic and organic pathologies of nervous system in the process of aging, memory impairments, dementia, schizophrenia and depressions. The poten-tial’s sensitivity to the condition of functional systems of patient’s brain allows tracking its dynamics during the treatment process.

P300 can be evoked by any sensory stimuli. The typical and most often used example is the presentation of the short tone bursts of two different frequencies in the random sequence. At passive listening waveforms for these two tones do not differ considera-bly. However if a patient is instructed to count or press the button every time a certain stimulus appears (meaningful stimulus) and to ignore the other one (non-meaningful), the additional positive component in the range from 250 to 450 ms (in average about 300 ms) appears in response to meaningful tone. The amplitude of the P300 is en-hanced when the meaningful stimulus is rare. As a rule, the probability of the mean-ingful stimulus is 20-30% of total stimulus quantity. P300 component can be sepa-rated from common components by computer subtraction of the responses to mean-ingful and non-meaningful stimuli.

As all cognitive EP, P300 is extremely sensitive to the habituation effect. That is why for its optimal recording it is required to use the minimum quantity of stimuli. However it should be enough to be sure it really differs from the current electrical brain activity (20-30 response averagings per meaningful stimulus).

P300 is the reflection of nonspecific brain activation connected with directed attention. P300 amplitude has age-related decrease. P300 amplitude depends directly on the at-tention degree. In case of ignoring the stimulus, its amplitude decreases and the la-tency increases. The relaxed condition of a patient impacts P300 in the same way.

MMN technique (Mismatch Negative, negative mismatch potential) is similar to P300, however instead of “meaningful” and “non-meaningful” stimulus, the notions “stan-dard” and “deviant” stimulus are used. Besides, the standard and deviant stimuli differ only slightly by their characteristics. The ideal MMN recording contains the difference between responses to standard and deviant stimuli in the range 100-200 ms.


124

14.2. Preparation to Acquisition

The recommendations for patient preparation and electrodes placement for auditory EP are practically the same as for cognitive EP.

Some researchers prefer to swap the non-inverting and inverting electrodes so that negative peaks on the recorded trace are directed upward. In this case P300 positive peak will be directed downward. Let’s consider the electrodes placement in case of using one amplifier channel:

inverting (-): vertex (Cz) or along the middle line of forehead on the hair growth bor-der (Fpz);

non-inverting (+): ipsilateral (tested) mastoid;

ground (common): contralateral mastoid.

When testing both ears using 2-channel recording, the non-inverting electrodes are placed on the mastoids (channel 1 – on the left mastoid, channel 2 – on the right mas-toid), the ground electrode – on a forehead (Fpz), and two inverting electrodes are combined by Y-adapter and placed on a vertex (Cz).

Before starting P300 acquisition, it is required to explain to a patient the essence of a test.

First of all, it is necessary to demonstrate to a patient both stimuli (meaningful and non-meaningful). To do this, use the buttons located in the bottom part of the main program window (Fig. 14.1). After pressing the button the corresponding stimulus will be presented until you click “OK” button in the dialog box that appears.

Fig. 14.1. The buttons for demonstration of P300 stimuli.

Second, it is required to tell a patient to count the number of meaningful stimuli by pressing patient’s button after each meaningful stimulus (preferable variant) or just counting in the mind. Any button of the two available on the device can be used.

For MMN testing, the stimuli counting is not needed.

When connecting a USB patient’s button device to the computer, please ensure that it’s connected to the same USB hub as Neuro-Audio digital sys-tem, otherwise the data concerning a patient’s response will be incorrect.

Cognitive EP Tests

125

14.3. Recommended Parameters Values

Table 13 represents the recommended parameters values for P300 acquisition.

Table 13. Parameters values for P300 acquisition

Meaningful stimulus: Modulated sinusoid, 50 ms, 2000 Hz, 85 dB SPL

Non-meaningful stimulus: Modulated sinusoid, 50 ms, 1000 Hz, 85 dB SPL

Stimulation frequency: 1 Hz


Filters: 1–35 Hz

Sweeps amplitude threshold: 300 µV

Meaningful stimulus probability: 30%

Waiting time for patient response: 500 ms

Maximum number of stimuli: 100

If excessive electrical line noise takes place during cognitive EP acquisition, you can switch on the adaptive notch filter.


For P300 acquisition, after a new exam creation, in the “New test” window select “Cognitive EP (P300)” in the list of test types and any template from the test templates list (by default 2 templates are available: 2-channel base and 1-channel).


Connect the headphones to the amplifier unit. Start acquisition with repetitive stimula-tion using the menu command Acquisition|Repetitive stimulation ([Ctrl+R]) and fol-low the process of signal averaging.


126

The order of signal recording from a patient and results analysis is described in chap-ter 8.4 “Acquisition and Analysis” (for ABR). The difference of cognitive EP test from other AEP tests is that responses are acquired separately for meaningful and non-meaningful stimuli (Fig. 14.2).

Fig. 14.2. P300 test window.

When a patient hears a meaningful stimuli, she/he must count them or press the pa-tient’s button. If the button is used during the acquisition, a statistics is maintained for the count of correct and incorrect (true and false) clicks and for patient’s response time.

After acquisition, patient’s response statistics can be viewed in the table and on the graph with “Response time” name (in Fig. 14.2 to the right at the bottom). In MMN test the patient’s button is not used and, correspondingly, the information concerning a pa-tient response time is not available in the analysis windows.

The trace name, patient’s average (mean) response time (ms), root-mean-square (RMS) deviation of patient response (ms), percentage of true clicks are displayed for each trace with meaningful stimulus. In the bottom part of the window there is the his-togram of patient response distribution by time for current (selected) trace with mean-ingful stimulus. Pay attention, if the current trace is the one acquired for non-meaningful stimulus, the given histogram will be empty.

To enhance the P300 or MMN component after the acquisition, you can subtract the traces to meaningful and non-meaningful stimuli using the menu command

Cognitive EP Tests

127

Trace|Calculate|Difference|Epochs. Before you do this, you should select the mean-ingful and non-meaningful traces using the mouse.


As stated above, you can find the specific parameters for each particular technique in the “Parameters” page of the test template dialog box (see the section 7.2. “Test Template Setup”). In this section the specific parameters for P300 technique are de-scribed (Fig. 14.3).

Fig. 14.3. Parameters for P300.

“Sweeps amplitude threshold (µV)” – a threshold value to reject native traces with lar-ger amplitude during the acquisition.

“Meaningful stimulus probability (%)” – the probability of meaningful stimulus emerg-ing during the stimulation (number of meaningful stimuli per hundred of stimuli).

“Waiting time for patient response (ms)” – the maximum time of patient response, i.e. time interval after meaningful stimulus, during which the click of a patient button is considered to be correct.

For MMN technique the settings are the same, only the last item is absent (since pa-tient’s button is not used in MMN).


128

15. Pure Tone Audiometry Test


Pure tone audiometry (PTA) is the key hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss. PTA is a subjective, behavioral measurement of hearing threshold, as it relies on patient response to pure tone stimuli. Therefore, PTA is used on adults and children old enough to cooperate with the test procedure.

The hearing threshold values are marked on audiogram. The audiogram is the graphi-cal visualization of a patient’s ability to hear pure tones of different frequencies (Fig. 15.1). The frequencies are marked on the horizontal axis of an audiogram. The vertical axis contains the stimulus intensity levels in dB relative to normal hearing thresholds: from -10 dB HL in the top part of audiogram to 110-120 dB HL near the basis.

Fig. 15.1. Audiogram of a person with high frequency hearing loss (air and bone conduction).

The pure tone audiometry has some advantages over other hearing assessment techniques (for example, ABR):

it detects accurate hearing thresholds for each ear;

it uses frequency-specific pure tone as a stimulus;

it uses both air and bone conduction.

However the pure tone audiometry is not ideal and cannot define all the types of hear-ing loss. That is why it is recommended to use it together with other techniques of hearing assessment.

Pure Tone Audiometry Test

129

Neuro-Audio-NET program supports the following set of frequencies for pure tone audiometry (for Neuro-Audio device): 125, 250, 500, 1000, 2000, 4000 and 8000 Hz.

Intermediate frequencies are also supported: 750, 1500, 3000, 6000 Hz. Also there is a high-frequency audiometry support (up to 16000 Hz), which requires the use of spe-cial high-frequency earphones (for example, Sennheiser HDA-300, Etymotic Re-search ER-2).

Pure tone is the stimulus, while white noise is used for masking. Stimulus intensity levels can be set in the range from -10 to 100-120 dB HL with 5 dB step (by default).

Pure tone audiometry can be performed both manually and automatically. This program provides the Hughson-Westlake automatic pure tone audiometry test used in most audiometers.

Neuro-Audio system is the IEC 60645-1: 2012 Type 4 screening audiometer (with some additional features, like white noise masking, bone conduction and sound field support).

15.2. Preparation to Acquisition

Use low-noise computers. If the computer emits great acoustic noise, the hearing thresholds for low frequencies (1000 Hz and lower) can be detected incorrectly (they will be overestimated).

Ideally the audiometry test requires the special sound-proof room. In case the study is performed in the conditions which do not correspond to standard requirements, the audiologist should remember that the surrounding noise can impact the audiometry results leading to increase of detected hearing thresholds. The problem of reduction of surrounding noise can be solved in two ways: the use of sound-proof chambers and special ear cushions or insert earphones. The insert earphones were developed to in-crease the accuracy of the audiometry study. Its application provides considerable advantages: the surrounding noise decreases by 30-40 dB; due to increase of inter-aural signal attenuation up to 70-100 dB, there is rarely a need to use the masking noise; reproducibility of test results increases; the possibility of external auditory mea-tus collapse is eliminated, which is very important for hearing assessment of children and some elderly patients.

It is required to explain to a patient that every time she/he hears the short tone, she/he should give a response: either using a hand gesture or pressing the patient’s button (any button on the device). Please, pay attention that during the automatic test the re-sponse waiting time is limited to an interval between stimulus (2 seconds or more).

When connecting a USB patient’s button device to the computer, please ensure that it’s connected to the same USB hub as Neuro-Audio digital sys-tem.


130

15.3. Recommended Parameters Values

Patient response for confirmation is 2 of 3.

The recommended parameter values for pure tone audiometry are listed in Table 14 and Table 15.

Table 14. Values of recording parameters for manual audiometry test.

Start level: 20 dB HL

Fixed tone duration: Switched off

Tone length: 1 s

Table 15. Values of recording parameters for Hughson-Westlake automatic test.

Tone length: 1 s

Start level: 20 dB HL

Random interval: 2–4 s

Maximum level: 80 dB HL

Minimum level: -10 dB HL


Since Neuro-Audio device is capable of producing sound pressure levels that are dangerous to hearing, software shows a warning on the info panel when sound intensity is above 100 dB HL (see Fig. 15.2).

Fig. 15.2. Warning indication above 100 dB hearing level.

For pure tone audiometry acquisition, after a new exam creation, in the “New test” window select “Pure-tone audiometry (PTA)” in the list of test types and press “OK” button.

The view of panel for pure-tone audiometry test control is represented in Fig. 15.3, and the view of the test window is given in Fig. 15.4.

Fig. 15.3. Panel for pure tone audiometry test control.


131

The panel contains two color indicators: “Tone” and “Response”. They can be switched on (green color) and switched off (black color).

“Tone” indicator is switched on when the tone signal is transferred to a patient head-phones and is switched off when the tone presentation is terminated.

“Response” indicator is switched on for a short period every time the program detects the patient’s response.

You can control the test in two ways: using the mouse (by pressing the corresponding buttons on the panel) or the keyboard.

By default, the following keys are used to control the main functions of pure tone au-diometry test (Table 16).

Table 16. Keys for audiometry control.

Key Function

Cursor up Increase intensity by 5 dB

Cursor down Decrease intensity by 5 dB

Cursor left Decrease tone frequency

Cursor right Increase tone frequency

[Alt] key Change stimulation side

[Space] key Play pure tone (by default – while the key is pressed)

[Enter] key Patient response (for manual entry by a doctor)

[A] key Run/stop automatic test (Hughson-Westlake)

[M] key Enable/disable masking noise

[Page Up] key Increase masking noise intensity by 5 dB

[Page Down] key Decrease masking noise intensity by 5 dB


132

Fig. 15.4. Pure tone audiometry test window.

15.4.1. Manual Test

During the manual test Neuro-Audio.NET program, as well as a hardware audiome-ter, requires pressing the “Tone” button ([Space] key) to present the tone to the headphones. By default, the tone is played while the button or key is pressed (during this time the “Tone” indicator on the control panel glows). In the settings (see chapter 0 “

Manual Test Settings”) you can specify fixed stimulus length (duration). It is recom-mended to present short stimuli (usually for not more than 1 second). It is necessary to wait for patient response for several seconds (usually for not more than 4 seconds after the tone playback). Also, to avoid the habituation, it is recommended to vary the intervals between the stimuli (within 2-4 seconds).

When a patient hears the stimulus (tone), she/he gives a response by pressing the patient’s button. If the button is missing, a doctor should press [Enter] key on the keyboard (or click “Response” button on the information panel using the mouse) as soon as she/he sees a patient’s gesture. In both cases “Response” indicator glows.

The test is started from a better hearing ear. If a patient can not define what ear hears better, usually the test is started from the right ear.

The test is usually started from 1000 Hz frequency. The signal presentation is started with intensity which is supposed to be perceived well by the given patient. Then the stimulus intensity level is decreased gradually with 5 or 10 dB step until the patient


133

stops recognizing it (descending stage). The intensity level is then increased with 5 dB step until the patient hears the stimuli again (ascending stage). For accurate detection of hearing thresholds, these stages are repeated 2-3 times.

By default, the “2 of 3” threshold detection method is used. It means that the program considers first two responses and in case they are received on the same intensity, this intensity is considered to be the hearing threshold for the given frequency. If the in-tensities are not equal, the third response is analyzed and is compared with the previ-ous two ones. If it equals one of them, it is a threshold. If all three responses are re-ceived on different tone intensities, the test is continued until two of three responses are equal.

When the threshold for frequency is detected, the test continues with the next fre-quency. The tones of different frequencies are usually presented in the following or-der: 1000, 2000, 4000, 8000, 500, 250, 125 Hz. When the thresholds are detected for all frequencies, proceed to test another ear.

15.4.2. Hughson-Westlake Automatic Test

When you run the automatic test, the program will perform the complete pure tone audiometry test of both ears using the standard Hughson-Westlake algorithm. To stop the test earlier, just press “Autotest” button once again (or [A] key on the keyboard).

First 1000 Hz frequency is set and the tone is automatically presented to the right ear with 20 dB HL intensity (with 1 second fixed length). The intervals between stimuli vary randomly within 2-4 seconds.

If initially there is no response from a patient, the intensity is increased by 20 dB with each next stimulus. After each response the intensity of next stimuli is decreased by 10 dB. If there is no response, it is increased by 5 dB.

By default, the “2 of 3” threshold detection method is used (as in manual test). When the threshold for frequency is detected, the test continues with the next frequency.

The frequency sequence for Hughson-Westlake automatic test is the following: after initial 1000 Hz the frequencies decrease. When the lowest frequency is reached (125 Hz), the test is continued with the frequencies higher than 1000 Hz. Then this se-quence is repeated for the left ear.

15.4.3. Masking

The pure tone audiometry without masking the opposite ear is successfully used for hearing thresholds detection in patients with normal hearing and patients with bilateral hearing loss. However, it cannot be used for patients with unilateral hearing loss and asymmetrical bilateral hearing loss (when the difference in thresholds of both ears is significant). When testing an impaired (or hearing worse) ear, the intensity of the pre-sented tone is so great that it is enough to distribute via the skull to the opposite (healthy or better hearing) ear, which perceives the presented tone on lower intensi-


134

ties than the studied ear. Due to this, the false thresholds are detected, which do not reflect the real ear condition.

Thus, at different stages of hearing impairment of right and left ears the danger of sig-nal rehearing is rather real. The false detection of conductive hearing loss when there is in fact a unilateral sensorineural hearing loss is, particularly, rather typical. The damping (masking) of unstudied ear with wide- or narrow-band noise helps preventing the erroneous results.

To apply correctly the damping (masking) of unstudied ear, it is required to have an idea of inter-aural signal attenuation value. The latter means the acoustic energy loss during passing of a sound through the scull tissues to the opposite ear. The inter-aural attenuation at the air conduction is 40-60 dB (depending on the frequency), and at bone conduction its value is even lower (from 0 dB on 250 Hz frequency up to 15 dB on 4000 Hz frequency). Using the insert earphones, it is possible to achieve the in-crease of inter-aural attenuation at air acoustic conduction up to 70 dB.

To activate the masking noise, open the test template settings window, select “Hard-ware” tab, than switch to “Stimulator” tab and after that check “Masking noise on” checkbox using the mouse. You can also specify its intensity there (see chapter 7.2.2 “Hardware”).

15.4.4. Classification of Hearing Loss Stages

The International classification of hearing loss stages based on the definitions of mean values of sound perception thresholds on 500, 1000, 2000 and 4000 Hz fre-quencies is given below (Table 17).

Table 17. International classification of hearing loss stages

Hearing loss stage Mean value of hearing thresholds on auditory frequencies (dB)

I 26–40

II 41–55

III 56–70

IV 71–90

Deafness Above 90


In chapter 7.2 “Test Template Setup” it was stated that “Parameters” tab of dialog box of test template settings contains specific parameters for the given technique. Here the parameters specific for pure tone audiometry technique are provided (Fig. 15.5).


135

Fig. 15.5. Parameters for pure tone audiometry.

“Answer of patient to confirm” – the number of patient’s responses (from last three re-sponses with the same intensity at which the program considers the given intensity value as a hearing threshold on the current tone frequency.

Most settings are divided into two groups: manual test and automatic test (Hughson-Westlake).

15.5.1. Manual Test Settings

“Start level (dB HL)” – the initial level of tone intensity (after each change of tone fre-quency).

“Fixed tone length” – it switches the mode of tone presentation. If the checkbox is un-checked, the tone is played while the button is pressed (mode by default). In case the checkbox is checked, the tone has fixed duration.

“Tone length (s)” – the tone duration in seconds (fixed tone duration mode) in the manual test.

“Silence mode (mouse hover)” – allows you to control tone levels and presentation by hovering the mouse cursor over the respective on-screen controls. This mode is es-pecially useful when the operator of the Neuro-Audio device and the patient are in the same room (to exclude unwanted noise of mouse clicking during test).

“Manual confirmation for intensities above 100 dB” – asks confirmation (once) when trying to set intensities above 100 dB (is checked by default). If unchecked, doesn’t ask confirmation. But the warning for such intensities is displayed in any case.

15.5.2. Automatic Test Settings

“Tone length (s)” – the fixed tone duration in seconds in the automatic test.


136

“Start level (dB HL)” – the initial level of tone intensity (after each tone frequency change) in the automatic test.

“Random interval (s)” – the variable interval between stimuli.

“Max level (dB HL)” – the maximum level of stimulus intensity in the automatic test.

“Min level (dB HL)” – the minimum level of stimulus intensity in the automatic test.

Bone Vibrator and its Application

137

16. Bone Vibrator and its Application

The bone vibrator as a stimulator is supported only by Neuro-Audio (2010 version) digital system.

The air conduction of stimuli was discussed before. However, in some cases the test of bone conduction is also required.

16.1. Applications

The bone vibrator is applied to estimate the cochlear reserve when determining the type of hearing loss. When the air conduction thresholds are elevated and acoustic immittance results are abnormal or questionable, it is recommended to use bone vi-brator to study bone conduction.

If you want to use bone vibrator as a stimulator, do the following:

connect the bone vibrator to the corresponding connector on the device (BC);

place the vibrator on a patient’s head;

select “Bone vibrator” from stimulator list on information panel (see Fig. 16.1).

Fig. 16.1. Parameters for audiometry.

Bone vibrator is most often applied to perform the following techniques:

ABR (there is a separate template for ABR – “Bone”);

pure tone audiometry.

In pure tone audiometry the thresholds are displayed separately on audiogram for air and bone conduction.

While recording ABR to study bone conduction, wave V is dominant on the trace. Big stimulus artifact often hides more early ABR components.


138

In adults, at similar intensity levels click-elicited wave V latencies at bone conduction are 0.5 ms longer than latencies at air conduction.

In infants, wave V latencies are shorter for bone-conduction clicks than air-conduction clicks.

Also, wave V thresholds for bone-conduction are lower in infants than adults for both click and 500Hz stimuli, with no difference seen for 4000 Hz.

16.2. Placement

The best place for setting the bone vibrator on patient’s head is a temporal bone. When you record bone-conduction ABR, the inverting (-) electrode should be placed at some distance from the oscillator to minimize stimulus artifact: an inferior postauri-cular location, on the earlobe, in the ear canal, or low on the nape of the neck.

16.3. Masking Noise

Analysis of test results involves comparing the wave V threshold for air-conduction and bone-conduction stimuli to estimate the amount of air-bone gap.

It is very important to apply the masking noise in contralateral ear whenever the pos-sibility of crossover is present.

Masking is needed for bone-conduction testing when the bone-conduction threshold differs from the air-conduction threshold of the same ear by more than 10 dB.

The need for masking noise limits the application of bone vibrator with Neuro-Audio (2010 version) device, since it does not support the simultaneous output of stimuli to bone vibrator and masking noise to the headphones.

neuro-audio.net um032.01.005.000 ec final · 1.2. program setup to install the neuro-audio.net...

Documents