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RAD 350 Chapt . 26 Digital Fluoro

RAD 350 Chapt . 26 Digital Fluoro. Terms to remember: DSA (digital subtraction angiography Registration Interrogation time Hybrid subtraction CCD ROI PACS. Advantages of DF over conventional. Speed of image acquisition Post processing “tweaking”

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RAD 350 Chapt . 26 Digital Fluoro

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  1. RAD 350 Chapt. 26 Digital Fluoro • Terms to remember: • DSA (digital subtraction angiography • Registration • Interrogation time • Hybrid subtraction • CCD • ROI • PACS

  2. Advantages of DF over conventional • Speed of image acquisition • Post processing “tweaking” • 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

  3. Pulsing Terms • Interrogation time = time to switch on and reach the mA and kVp level • Extinction time = time for the tube to be switched off (usually times less than 1 ma)

  4. 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 TV cameras • This results in much HIGHER SNR than conventional TV cameras/systems • They also have NO log time or “blooming” and require NO maintenance • CCD’s can be “docked” directly to the II’s output phosphor

  5. 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 dose

  6. DR Subtraction (2 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

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

  8. DF/D Subtraction Dose • DF & D subtraction usually result in much higher patient dose and PULSED imaging is required to lower it! • Storage and image distribution as already discussed are utilized

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