Computed Tomography (CT) Retrospective/Prospective

1. Computed Tomography (CT)Retrospective/Prospective Radiation Protection and Control for New Applications of Existing Technology Robert M. Gagne, Ph.D. Office of Science and Technology TEPRSSC 2000

2. What are the objectives of the presentation? • Update on actions pertaining to Computed tomography fluoroscopy (CTF) • Take a retrospective look at CDRH activities in the CT arena • Take a prospective look at new applications of CT equipment • Identify any unique radiation protection and safety considerations TEPRSSC 2000

3. CTF - Special Interest • Dose and imaging performance of computed tomography fluoroscopy (CTF) • new real time imaging application for existing technology (CT) • similarities between traditional interventional fluoroscopy and CTF • sensitize users to exposure levels and possibility of radiation injuries TEPRSSC 2000

4. CTF - General Description • Continuous scans of a section of the patient • 50 seconds of CTF at 1 rotation per second • 50 rotations of x-ray tube about the patient • Cross-sectional images updated at a rate of 6-9 images per second • “real time” imaging • If no patient motion during procedure, one strip of skin gets the “full brunt” of the radiation exposure TEPRSSC 2000

5. Entrance Dose CTF 1 - pre market submittal 2 - Nawfel et al, AAPM Annual Meeting (1998) na - not available TEPRSSC 2000

6. X-Ray Fluoroscopy or X-Ray CT? • Applicability of requirements in Performance Standard • difficult, if not impossible, to fit to CTF • how to regulate appropriately? • Short and long term actions • in process • data gathering (NEXT 2000) • possible amendments to Performance Standard TEPRSSC 2000

7. CT - Retrospective Look • Amendments to Performance Standard (21CFR1033, Sept 1985) • dose labeling in User Manual • performance criteria for light localizers and table increment • CT characteristics at the time • 10 mm slice thickness • contiguous scans and consecutive table increment TEPRSSC 2000

8. CT - Axial Scanning(10 mm slice) X,Y Table motion after scan complete Tissue Imaged Volume TEPRSSC 2000

9. CT - Retrospective Look • Relevance and adequacy of regulations for new applications of CT equipment • Helical or spiral CT • fast scanning technique • new technological considerations • New CT applications • CTF • angiography • multiphase contrast studies TEPRSSC 2000

10. CT - Spiral Scan(10 mm slice, 2:1 pitch) X,Y Z Table Motion Tissue Imaged Volume TEPRSSC 2000

11. CT - Prospective Look • Multi-slice spiral CT • fast volume scanning technique • renaissance in CT TEPRSSC 2000

12. CT - Multi Slice Spiral Scan(2-10 mm slices, 1:1 pitch) X,Y Z Table Motion Tissue Imaged Volume TEPRSSC 2000

13. State of the Art Images TEPRSSC 2000

14. Radiation Protection and Safety • Relative contribution of CT to the dose per capita • Fraction of all radiological examinations (3-4 %) • 10 - 40 % of total dose contribution TEPRSSC 2000

15. Radiation Protection and Safety TEPRSSC 2000

16. Use, Education and Training • Selection of operating parameters • strong dependence on dose • User training and education • complicated equipment • analogy to interventional fluoroscopy • sensitivity to possible exposure levels • European approach • reference dose values and related guidelines TEPRSSC 2000

17. Physical and Technical Aspects • Added filtration, shaped filters, detector technology • improvements by percent not factors • Automatic exposure control • low attenuation = low mAs • for example, pediatric vs adult patients • AP vs LAT projections within a scan • not available in CT TEPRSSC 2000

18. Summary • Renaissance in CT • new applications with significant benefits • Have user and equipment programs kept up with changes? • Dose per capita significant • fertile area for dose improvement with an impact • Open for suggestions • not necessarily regulatory approaches TEPRSSC 2000