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RAD 354 Chapt. 26 Digital Imaging Many types/names for the digital imaging to come – Types CR: Barium fluorohalide PSP SPR (scan projection RAD): Nal scintillator/photodiode.

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Presentation on theme: "RAD 354 Chapt. 26 Digital Imaging Many types/names for the digital imaging to come – Types CR: Barium fluorohalide PSP SPR (scan projection RAD): Nal scintillator/photodiode."— Presentation transcript:

1 RAD 354 Chapt. 26 Digital Imaging Many types/names for the digital imaging to come – Types CR: Barium fluorohalide PSP SPR (scan projection RAD): Nal scintillator/photodiode Indirect DR: Csl, Gdos scintillator (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 Subtraction TWO Primary Types Temporal subtraction – Single kVp setting – Normal filtration – Good contrast resolution 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

20


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