OVERVIEW OF DIGITAL IMAGING AND RADIATION PROTECTION ISSUES

1. 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] Robert M. Gagne

2. 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 Robert M. Gagne

3. 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? Robert M. Gagne

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

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

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

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

8. CCD based - lens coupled DR system [From: P. Sund et al, Proc. SPIE 3977: 437; 2000] CCD based - fiber optic coupled DR system [From: Handbook of Medical Imaging, Volume I., Chapter 4, J. Beutel et al, eds, SPIE Press 2000] Pixel Elements (3000 x 2500) Pixel Element ( 0.14 mm x 0.14 mm ) Robert M. Gagne

9. 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? Robert M. Gagne

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

11. Film/Screen “Speed” Difference in speed of about 2 • 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 Robert M. Gagne

12. 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? Robert M. Gagne

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

14. 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 Robert M. Gagne

15. Digital Radiography System Visible light X-rays CCD Camera (image) Lens - Not all but focus on those with large object and small image - Less than 1 % of light photons make it to film!! Phosphor (object) Digital Radiography (CCD based - lens coupled) • Careful system design to overcome inefficiencies Robert M. Gagne

16. 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] Robert M. Gagne

17. 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 Robert M. Gagne

18. 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 Robert M. Gagne

19. 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 Robert M. Gagne