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
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 prept 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
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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 pt. dose
CCD
DR Subtraction
TWO 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
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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 $$$
Con’t
Con’t