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TERPSSC 2001 Robert M. Gagne

What is the purpose of this

presentation? Here are a couple reasons:

interest in digital imaging!

some concerns related to radiation

safety and effectiveness

potential for exposure increase

(and/or reduction??)

Forces a re-visit of some actions

in the far radiological health past

imaging system inefficiency

Review of options (regulatory or

otherwise) for dealing with actual

and/or perceived concerns

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What kind of equipment?

Digital radiography (DR)

not digital fluoroscopy using CCD

cameras

not film digitizers

Three different types of DR

systems

flat panel imaging arrays

computed radiography systems

CCD based - optically coupled

systems

What are the concerns?

No equivalence to "speed" or self

limitation as in screen/film systems

Inefficient" systems possible?

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Flat Panel Imaging Arrays

(indirect conversion)

Image Formation

[From: Medical Imaging, 2000]

[From: Handbook of Medical Imaging, Volume I.,

Chapter 4, J. Beutel et al, eds, SPIE Press 2000]

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(direct conversion)

Image Formation

[From: Medical Imaging, 2000]



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Number of Pixel Elements (3000 x 2500)

Pixel Element Size ( 0.14 mm x 0.14 mm )






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Computed Radiography

Image Formation

Pixel Elements ( 0.2mm x 0.2 mm )

Pixel Elements(2160 x 1800)


Chapter 5, M. Yaffee, eds, SPIE Press 2000]

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CCD based - lens coupled DR system

Pixel Element ( 0.14

mm x 0.14 mm )

Pixel Elements

(3000 x 2500)

CCD based - fiber optic coupled DR system[From: Handbook of Medical Imaging, Volume I.,


[From: P. Sund et al,Proc. SPIE 3977: 437; 2000]

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What are radiation

protection and safety issues?

Unique characteristics of

screen/film imaging systems

self limitation of patient

exposure

concept of "speed" defined and

understood

New considerations for digital

radiography

no self limitation as in

screen/film systems

no consensus on speed

"inefficient" systems possible?

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Film/Screen Speed

Film/screen speed

speed = 100/E where E is exposure in

mR to produce an optical density of

1.0

position on exposure axis dependenton speed

higher speed number translates to

lower patient exposure

Difference

in speed

of about 2

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DR Speed

DR operating point

equivalence to film/screen speed set

at installation?

no self limitation except at extreme

ends of the gray-scale transfer curvepatient exposure increase / decrease /

equivalence compared to film/screen?

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 20 40 60 80 100 120

Relative Exposure

PixelValue

Gain 1

Gain 2

Gain 3

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Imaging System Inefficiency

Chest radiography - screening program(60s-70s) for cardiopulmonary disease

need for rapid, economical imaging system

Photofluorographic (PFG) imaging

system mobile vans

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Public Health Concerns

Low detection rate for tuberculosis,

heart disease, and other respiratory

diseases

High patient radiation exposure vs

conventional screen/film radiography

BRH develops standard technique for

estimating patient exposure

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Digital Radiography

(CCD based - lens coupled)

X-rays

Visible

light

Phosphor

(object)

Lens

- Not all but focus on those withlarge object and small image

- Less than 1 %of light photons

make it to film!!

CCD

Camera

(image)

Digital

Radiography

System

Careful system design to overcome

inefficiencies

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Options

Tracking exposure levels

NEXT 2001 chest radiography

diagnostic reference levels (ICRP,

AAPM, many others)

practical tools for managing radiation

dose levels to patients

Quality assurance programs

Performance evaluation of

Computed radiography system,

Med. Phys. 28(3), March 2001

Diagnostic x-ray Performance

Standard

performance requirements on levels

of imaging performance such asdetective quantum efficiency (DQE)

dose display at operators console

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Dose Display

Previous slide describes several viable

options TEPRSSC radiation standards and

safety committee

Diagnostic x-ray Performance

Standard

dose display at operators console for all

radiographic equipment

Practical considerations yet to be

explored or evaluated

cost

effectiveness

alternatives?

dose descriptor and definition?

tie to diagnostic reference levels

effective resource allocation

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