1/29/13

1

SCANNER CONTROL PANEL

Monitor

image display

List of patients exam

Measurement

1/29/13

2

When scanning patient first select patient schedule

Select patient name and exam

Next select protocol icon

1/29/13

3

1/29/13

4

1/29/13

5

Scan Type

Axial Scan Mode

Data acquisitions each slice / volume is taken and then the table is incremented to the next location to collect data over a longer z axis range

Usually use doing biopsy, drain, mylogram

With Inter Scan Delay

Inter Scan Delay = is a small delay between slices or volumes that is needed druing standard axial scanning for the x-ray tube to stop and reverse direction. Inter Scan delay can also be use to allow extra time during a scan for tube cooling

1/29/13

6

Helical / Spiral

Helical scan is a very fast way to examine the target anatomy

The volume is scanned very quickly because the table is in a constant

motion as the gantry rotates continuously

Scan in a single breath hold

Greater accuracy for multiplanar & 3D images

Faster scanning less contrast use

There is no inter scan delay between slices as in an axial acquisition

Cine

This is used in Perfusion applications to evaluation blood flow, blood volume and mean transit time

Cine is a time sequence of axial images

Uses full rotations while gathering input from the same location over a

period of time

1/29/13

7

Cine Brain Perfusion

Start - End =Number of images

1/29/13

8

Thick Speed

1/29/13

9

Detectors

Multirow detector consists of one detector with rows of detector elements

Recall third and forth generation scanner

Solid State detectors can acquire four slices per 360 degree rotation

1/29/13

10

Single Detector vs Multi-row Detector

Single Detector vs Multi-row Detector

Single Detector Array

One detector, 15mm long in z direction

Multiple rows Detector

Larger coverage and faster scan times, high

detail slice images or 3 D volume images, less radiation dose, less motion artifacts, better bolus tracking

1/29/13

11

Detectors

Collimation

Collimation selection also depends on the type of tissue to be examined

Smaller structures usually require narrow collimation

Larger structures are imaged with wider collimation

1/29/13

12

Scanner Control Panel

1/29/13

13

Bow Tie Filter Selection

Scan Field of View (SFOV)

Is the area that is being scanned

There are small, medium, large SFOV depending on the exam

1/29/13

14

CT Scan Parameters Video

http://www.youtube.com/watch?v=T7L-9-fh49s

Affecting Pitch

1/29/13

15

Pitch

Pitch

The distance ( in mm) that the CT table moves during one revolution of x-ray tube

The pitch specifies the extent to which the x-ray helix is stretched

1/29/13

16

kV & mA

kV is usually chosen from 80 kV to 140

There are three option for mA

Manual mA

Auto mA

Smart mA

mA

Manual mA is chosen by tech

Auto mA is an automatic

exposure control system for CT

1/29/13

17

mA Table

The mA table reports what the mA will be for scan each scan rotation based on the factors you have set on the AutomA control.

These factors are applied to the patient data gathered for the last scout taken typically AP

mA Tables

1/29/13

18

AutomA

AutomA is an automoatic exposure control system use that employs Z axis tube current modulation

The benefit is to maintain a constant photon exposure for consisten image quality while providing dose resudtin to the patient

AutomA will use the last scout taken to compute the require mA. The lowest dose will be computed from an AP scout. You can use Lateral scout but it will increase dose.

AutomA changes mA across the z axis

1/29/13

19

Position Accuracy

Position Accuracy

Proper patient positioning will help give accurate dose by positioning the body at isocenter.

The need to increase mA to compensate for the noise is eliminated

1/29/13

20

Smart mA

Auto mA must be selected first then Smart mA is available.

Smart mA changes the mA across the x/y axis within a slice

mA Tables

1/29/13

21

Smart mA

Noise & Noise Index

1/29/13

22

Total Exposure Time

1/29/13

23

ScanTiming

Pre Group: The time set for the scan to start after pressing the start button on keyboard

ISD (Inter-Scan Delay): A delay between exposures

Breath Hold: The amount of time the patient will be holding their breath during exposure

Scan Timing

Breath Time: If scan time is longer than set breath hold a second scan can be set to follow that allows for a period of time for the patient to breath before the next scan begins

Auto Voice: Can be set according to protocol for Inspiration, Expiration, Hyperventilation, etc

1/29/13

24

Scan Parameters

Image Reconstruction

1/29/13

25

Reconstruction Data

Reconstruction data are convolved data that have been back projected into the image matrix to create CT image displayed on a monitor

Various digital filters are available to suppress noise and improve detail

Reconstruction Data

There are three different types of algorithms

Standard

Bone

Detail

1/29/13

26

Reconstruction Algorithms

Standard algorithms - provides good contrast resolution

Bone algorithms - helps optimize spatial resolution but produces poor

contrast resolution

Detail algorithms - give adequate contrast resolution with good edge definition

Algorithm

Standard

Detail

1/29/13

27

Algorithm

Bone

ASIR

Adaptive Statistical Iterative Reconstruction

First software from GE to clean up CT images and in the process allow

dramatic reduction up to 50% in patient radiation dose

It is a Noise reduction edge enhancement algorithm

1/29/13

28

ASIR

Understanding the Dose Equation

The decision to adjust scan parameters involves understadning the method for estimating dose

There are 3 factors that are used to estimate effective dose

Phantom

CTDI vol = Computer Tomography Dose

Index

DLP = Dose Length Product

1/29/13

29

Dose

1/29/13

30

Dose

Phantom =The size of phantom is either small (16cm diameter) or large (32 cm diameter) depending on the size of the body part. The actual dose to patient is dependent on body habitus as compared to that of the reference phantom

DLP = is representative of the total dose delivered

CTDI vol = is the dose index used for CT scanning

to represent the average dose for the area scanned.

CT Dose and Risks

http://www.youtube.com/watch?v=hi0H6eUWyh4

1/29/13

31