RAD 354 Chapt . 26 Digital Imaging

1. RAD 354 Chapt. 26Digital Imaging • Many types/names for the digital imaging to come • Types • CR: Barium fluorohalide PSP • SPR (scan projection RAD): Nalscintillator/photodiode • Indirect DR: Csl, Gdosscintillator (Cesium Iodide ; Gadolinium) • Indirect DR: Csl/Charge coupled device (CCD) (amorphous selenium) • Direct DR: a-Se, Thin-film transistor

2. ES’s “Clever approach” (capture element, coupling element, collection element • “Capture element” how the x-rays are captured (PSP’s, Csl,. Gado, etc.) • “Coupling element” transferring the x-ray “signal” to the collection element • “Collection element” devices to either collect light photons or electrons

3. Scan Projection Radiography • As in CT, uses a “fan beam” (collimated by pre-pt collimators), Post pt., remnant beam is collimated to form a “fan” for the detector array – Neither the tube OR detector move! • SPR is NOT too successful, but is hanging around

4. Charge Coupled Devices • CCD’s are SMALL, thus GREAT for digital imaging • Have HIGHJ sensitivity to radiation and WIDE dynamic range (dim to bright light) • STRAIGHT H & D “CURVE”

5. Types of CCD’s • Cesium Iodide/CCD • Cesium Iodide/Amorphus Silicon • Amorphous Selenium

6. RAD 354 Chapt. 27 Digital Fluoro • Terms to remember • DSA – digital subtraction angiography • Registration • Interrogation time • Hybrid subtraction • CCD = charge coupled device • ROI = region of interest • PACS = picture archival and communication system

7. Advantages of DF • Speed of image acquisition • Post processing “tweaking” of the image(s) • Spatial resolution is determined by the matrix size (usually 1024 X 1024) and the size of the image intensifier) • DF operates at “conventional mAs” (hundreds of mA rather than less than 5 mA as conventional fluoro) • BUT – DF operates in “pulsed, progressive” fluoro!

8. “Pulsing” Terms • Interrogation time = time for unit to be switched on and reach the mA and kVp level • Extinction time = time for the tube to be switched off (usually times less than 1 ms)

9. Receptor • The “receptor” is usually a “charge coupled device” (CCD) • CCD’s are VERY sensitive to light and have a much LOWER level of noise than a TV camera • This results in much HIGHER SNR than conventional TV cameras/systems • They also have NO lag time or “blooming” and require NO maintenance • CCD’s may be “docked” directly to the II’s output phosphor

10. Advantages of CCD’s • High spatial resolution • High SNR • High Detective Quantum Efficiency (DQE) • No warm up required No lag/blooming • No spatial distortion/maintenance • Unlimited life • Unaffected by magnetic fields • Lower pt. dose

11. CCD

12. DR SubtractionTWO Primary Types • Temporal subtraction • Single kVp setting • Normal filtration • Good contrast resolution (1% @ 1 mm) • Simple arithmetic image subtraction used • Motion artifacts are a problem (misrepresentation) • Total subtraction is able to be achieved • Subtraction limited by number of images

13. Energy Subtraction • Rapid voltage switching is used • Filter switching is preferred • Higher x-ray energy used for + contrast resol. • Complex image subtraction is required • Motion artifacts (misrepresentation) are reduced • Some residual bone is survived (shows) • More types of subtraction are possible • IF BOTH ARE COMBINED = HYBRID SUBTRACTION

14. DF/D Subtraction RAD Dose • DF & D Subtraction usually result in much higher pt. dose and PULSED imaging is required to lower the dose! • Storage and image distribution are used as already discussed in class

15. Images

16. Lateral Cerebral DSA

17. DSA Hand

18. Latest in hybrid digital fluoro(Sunrise Hospital – 3.9 million $$$

19. Con’t

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