# Presentation: 922578

## 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

- June 21, 2000

## 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

- June 21, 2000

## 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

- June 21, 2000

## 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

- June 21, 2000

## CTF

**Entrance Dose**

- 1 - pre market submittal
- 2 - Nawfel et al, AAPM Annual Meeting (1998)
- na - not available

- TEPRSSC 2000

- June 21, 2000

## 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

- June 21, 2000

## 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

- June 21, 2000

## CT - Axial Scanning(10 mm slice)

- X,Y

- Tissue Imaged Volume

- Table motion after scan complete

- TEPRSSC 2000

- June 21, 2000

## 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

- June 21, 2000

## CT - Spiral Scan(10 mm slice, 2:1 pitch)

- X,Y

- Tissue Imaged Volume

- Z

- Table Motion

- TEPRSSC 2000

- June 21, 2000

## CT - Prospective Look

**CT - Prospective Look**

- Multi-slice spiral CT
- fast volume scanning technique
- renaissance in CT

- TEPRSSC 2000

- June 21, 2000

## CT - Multi Slice Spiral Scan(2-10 mm slices, 1:1 pitch)

- Z

- X,Y

- Tissue Imaged Volume

- Table Motion

- TEPRSSC 2000

- June 21, 2000

## State of the Art Images

- TEPRSSC 2000

- June 21, 2000

## 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

- June 21, 2000

## Radiation Protection and Safety

- TEPRSSC 2000

- June 21, 2000

## 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

- June 21, 2000

## 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

- June 21, 2000

## 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

- June 21, 2000