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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” • 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 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) 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 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 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 • 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 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