Transcript 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”
• 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
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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