1. TERPSSC 2001Robert M. Gagne OVERVIEW OF DIGITAL IMAGING AND RADIATION PROTECTION ISSUES Robert M. Gagne MICAB/DECS/OST rmg@cdrh.fda.gov [From: Handbook of Medical Imaging, Volume I., Chapter 4, J. Beutel et al, eds, SPIE Press 2000]

2. TERPSSC 2001Robert 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

3. TERPSSC 2001Robert M. Gagne 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?

4. TERPSSC 2001Robert M. Gagne 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]

5. TERPSSC 2001Robert M. Gagne Flat Panel Imaging Arrays (direct conversion) Image Formation [From: Medical Imaging, 2000] [From: Handbook of Medical Imaging, Volume I., Chapter 4, J. Beutel et al, eds, SPIE Press 2000]

6. TERPSSC 2001Robert M. Gagne Number of Pixel Elements (3000 x 2500) Pixel Element Size ( 0.14 mm x 0.14 mm ) Flat Panel Imaging Arrays [From: Handbook of Medical Imaging, Volume I., Chapter 4, J. Beutel et al, eds, SPIE Press 2000]

7. TERPSSC 2001Robert M. Gagne Computed Radiography Image Formation Pixel Elements ( 0.2 mm x 0.2 mm ) Pixel Elements (2160 x 1800) [From: Handbook of Medical Imaging, Volume I., Chapter 5, M. Yaffee, eds, SPIE Press 2000]

8. TERPSSC 2001Robert M. Gagne 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., Chapter 4, J. Beutel et al, eds, SPIE Press 2000] [From: P. Sund et al, Proc. SPIE 3977: 437; 2000 ]

9. TERPSSC 2001Robert M. Gagne 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?

10. TERPSSC 2001Robert M. Gagne Film/Screen “Self Limitation” Imaging task with large dynamic range Be careful not to under or over expose film “Self limitation” of patient exposure

11. TERPSSC 2001Robert M. Gagne 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 dependent on “speed” –higher “speed” number translates to lower patient exposure Difference in speed of about 2

12. TERPSSC 2001Robert M. Gagne 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 curve –patient exposure increase / decrease / equivalence compared to film/screen?

13. TERPSSC 2001Robert M. Gagne Imaging System Inefficiency Chest radiography - screening program (60s-70s) for cardiopulmonary disease –need for rapid, economical imaging system Photofluorographic (PFG) imaging system –mobile vans

14. TERPSSC 2001Robert M. Gagne 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

15. TERPSSC 2001Robert M. Gagne Digital Radiography ( CCD based - lens coupled) X-rays Visible light Phosphor (object) Lens - Not all but focus on those with large 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

16. TERPSSC 2001Robert M. Gagne Level of Public Health Concern Installation base is small (even smaller for CCD based - lens coupled systems) –computed radiography not included Basic questions: Is there evidence of higher patient radiation exposure with these imaging systems screen/film radiography? [From: Medical Imaging, 2000]

17. TERPSSC 2001Robert M. Gagne 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 as detective quantum efficiency (DQE) –dose display at operator’s console

18. TERPSSC 2001Robert M. Gagne Dose Display Previous slide describes several viable options –TEPRSSC radiation standards and safety committee Diagnostic x-ray Performance Standard –dose display at operator’s 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

19. TERPSSC 2001Robert M. Gagne Summary Different types of DR –flat panel imaging arrays –computed radiography systems –CCD based - optically coupled systems Radiation safety and effectiveness issues –no equivalence to "speed" as in screen/film systems –"inefficient" systems –present revisits the past –potential for exposure reduction and/or increase?? Options for dealing with perceived and/or actual concerns –one suggested regulatory approach