RAD 354 Chapt. 26Digital 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

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

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

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”

Types of CCD’s

• Cesium Iodide/CCD• Cesium Iodide/Amorphus Silicon• Amorphous Selenium

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

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!

“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)

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

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

CCD

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

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

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

Images

Lateral Cerebral DSA

DSA Hand

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

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