medical instrumentation application and...

Medical Imaging &

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BioinstrumentationMedical Instrumentation: Application and Design Third Edition

John G. Webster, Editor

Kuo-Sheng Cheng, Ph.D.

Department of Biomedical Engineering

National Cheng Kung University

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The Importance of Medical

Instrumentation

• Diagnosis and therapy depend heavily on

the use of medical instrumentation.

• Medical procedures:

Medicine can be defined as a multistep procedure

on an individual by a physician, group of

physician, or an institute, repeated until the

symptoms disappear.

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The Importance of Medical

Instrumentation

• Medical procedure

– 1) Collection of data - qualitative and/or

quantitative

– 2) Analysis of data

– 3) Decision making

– 4) Treatment planning based on the decision

– 5) Repeat

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A Story of New Medical Device

• The invention, prototype design, product

development, clinical testing, regulatory

approval, manufacturing, marketing, and

sale of a new medical instrument add up a

complex, expensive, and lengthy process.

• A success story - Technicon’s Auto

Analyzer

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Development of Technicon’s Auto

Analyzer

• The inventor - Leonard Skeggs,

• Chair of Department of Pathology at Case

Western Reserve University - Dr. Alan

Moritz

• Technicon Corporation founders - Edwin C.

Whitehead, and his father

• a four-page confidential disclosure form

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Development of Technicon’s Auto

Analyzer

• Two key persons to recall the invention -

Technicon’s only salesman, Ray Roesch,

and the doctor at the Cleveland Veterans

Adminstration Hospital, Joseph Kahn.

• Patent application and protection

• Marketing strategy

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Development of Technicon’s Auto

Analyzer

• Factors affected the success

– it allows an enormous improvement in quality

of laboratory test results, and an enormous

reduction in the cost of doing chemical analysis.

– accurate laboratory data are useful in diagnosis.

– reimbursement policies increase the availability

of health care.

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• Evolutionary product v.s. Revolutionary

product

• Generalized medical instrumentation system

– measurand

– sensor

– signal conditioning

– output display

– auxiliary elements

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Figure 1.1 Generalized instrumentation

Perceptible

outputOutput

display

Control

And

feedback

Signal

processing

Data

transmissionData

storage

Variable

Conversion

element

Sensor

Primary

Sensing

element

Measurand

Calibration

signal

Radiation,

electric current,

or other applied

energy

Power

source

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Alternative Operational Modes

• Direct-Indirect modes

• Sampling and Continuous modes

• Generating and Modulating sensors

• Analog and Digital Modes

• Real-time and Delayed-time Modes

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Medical Measurement Constraints

• Many crucial variables in living systems are

inaccessible.

• Variables measured are seldom

deterministic.

• Nearly all biomedical measurements depend

on the energy.

• Operation of instruments in the medical

environment imposes important additional

constraints.

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Classifications of Biomedical

Instruments

• The sensed quantity

• The principle of transduction

• The organ system for measurement

• The clinical medicine specialities

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Classifications of Biomedical

Instruments

• Based on the activities involved in the

medical care, medical instrumentation may

be divided into three categories:

– diagnostic devices

– therapeutic devices

– monitoring devices

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Generalized Static Characteristics

• Accuracy

• Precision

• Resolution

• Reproducibility

• Statistical control

• Static sensitivity, Sensitivity drift

• Zero drift

• Linearity

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Figure 1.3 (a) Static-sensitivity curve that relates desired input xd to output y.

Static sensitivity may be constant for only a limited range of inputs. (b) Static

sensitivity: zero drift and sensitivity drift. Dotted lines indicate that zero drift

and sensitivity drift can be negative.

Intercept bDxd

Dy

D x'd

D y'

y (Output)

y = mxd + b

xd (Input)

(a)

Slope m =Dy

Dxd

Total error due to drift

Characteristic with zero and sensitivity drift

+ Zero

drift

+ Sensitivity

drift

- Sensitivity drift

- Zero drift

(b)

y (Output)

xd (Input)

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Generalized Static Characteristics

• Input ranges

• Input impedance

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Generalized Dynamic Characteristics

• Differential or Integral equations

• Transfer functions

• Time delay

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Figure 1.8 Design

process for medical

instruments Choice

and design of

instruments are

affected by signal

factors, and also by

environmental,

medical, and

economic factors.

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Regulation of Medical Devices

• 1976 - Medical Device Amendments to the

Federal Food, Drug, and Cosmetics Act

• 1990 - Safe Medical Devices Act

Medical Device: any item promoted for a

medical purpose that does not rely on

chemical action to achieve its intended

effect

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Regulation of Medical Devices

• Medical devices were classified in two

ways:

– Class I (general controls), Class II

(performance standards), and Class III

(premarketing approval)

– Preamendment, Postamendment, Substantially

equivalent, implant, custom, investigation, and

transitional.

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Biomedical Transducer

Measuring is the key to understand, and transducer plays

an important role in measurement.

Kuo-Sheng Cheng, Ph.D.

Institute of Biomedical Engineering

National Cheng Kung University

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What is the Transducers?

• In principle, Transducers are devices that

convert signals in one form of energy into

signals in another form of energy.

• Sensors

• Actuator

• Conventional v.s. Intelligent Transducers

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What are the Transduers, Sensors, and

Actuators?

• Transducer - A device that converts energy

of one form to another.

• Sensor - A device that converts a physical

parameter to an electric output.

• Actuator - A device that converts an electric

signal to a physical output.

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Conventional v.s. Intelligent

Transducer

• Conventional transducer

SensorTransmission

Link

Signal

Processing

Display

Storage

Actuator

...

Further

Processing

Physical

or

Chemical

Parameters

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Sensing Element

&

Signal Processing

Transmission

Link

Conventional v.s. Intelligent

Transducer

• Intelligent transducer

Physical

or

Chemical

Parameters

Signal

Processing

Display

Storage

Actuator

...

Further

Processing

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Transducer Categories

• By application

• By physical or chemical principles used

• By the process used to convert the signal

energy into an electrical signal

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Three types of output signal

• Self-generating (active) transducers:

– The electrical signal output of transducer is

generated from another form of input energy.

e.g.

Light

in ~ RLI

Photovoltaic cell

Electrical

Signal

Output

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Three types of output signal

• Modulating (passive) transducer:

– The input signal energy of transducer is used to

modulate the electrical energy flow from the

power supply to the transducer output.

e.g.

Light

in RLI

Photoconductive cell

Electrical

Signal

Output

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Three types of output signal

• Tandem transducers:

– The original input signal energy is converted to

a final output of electrical energy through two

or three effects or conversions in tandem.

e.g.Light in

Y-position

RLI

Photoconductive cellElectrical

Signal

OutputModulated

light

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1. Sensor characteristics

2. Physical Sensors

• Displacement measurements

• Resistive

• Capacitive

• Inductive

• Piezoelectric

• Temperature measurements

• Optical measurements

3. Chemical Sensors

• Biochemical

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Electronic Sphygmomanometer

Student: Cheng-Yu Chen

Advisor: Kuo-Sheng Cheng

Biomedical Imaging & Instrumentation Lab

The System Design & Analysis

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Introduction

• The blood pressure measurement

-Invasive methodStephen Hales placed a glass tube in the artery of horse for blood

pressure measurement in 1733.

The measurement of blood pressure with a mercury sphygmomanometer

was first invented by J. M. Poiseuille in 1828.

-Noninvasive methodLimb-occluding device that contained an arm cuff was first invented by

S. Riva-Rocci in 1896.

L. Hill and H. Barnard published a modified sphygmomanometer with

cuff in 1898.

N. S. Korotkov invented an auscultatory measurement of systolic and

diastolic blood pressure in 1905.

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Introduction (cont.)

• Stephen Hales demonstrated the

blood pressure in horse in 1733.

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Introduction (cont.)

• Riva-Rocci’s sphygmomanometer, 1896

• Blood pressure measurement using Korotkov’s method, 1905

*E. O’Brien and D. Fitzgerald, “The history of indirect blood

pressure measurement,” Handbook of Hypertension, Vol. 14: Blood

Pressure Measurement

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Introduction (cont.)

• Korotkov’s method

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Introduction (cont.)

• The oscillometric method

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System Description

Display unitRS-232 Data

transmission

Air pump & valve

control circuit

Microprocessor

with A/D converter

Cuff Pressure

Sensor

Instrumentation

Amplifier

High-Pass Filter

Low-Pass Filter

Analog signal

processing Circuits

Pressure

Signal

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Hardware Design

• The system circuits

Microprocessor

With A/D

Converter

Display Unit

RS-232 Data

Transmission

Air Pump & Valve

Control Circuit

Pressure

Sensor

Analog Signal

Processing Circuit