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Imaging CH.12

Computed Radiography

Question	Answer
PSL (Photostimulable luminescence)	Emission of a visible light after excitation by a laser.
PSP (Photostimulable phosphor)	-The phosphor used in the screens in digital imaging. -Usually barium fluorohalide.
SPS (Storage Phosphor Screen)	Phosphor screen that hold the latent image in digital imagin.
IP (Imaging Plate)	The "cassette" which holds the SPS in digital imaging.
SP (Storage Phosphor)	Phosphors within the CR cassette.
PMT (Photomultiplier Tube)	Light detectors in CR imaging.
PD (Photodiode)	Light detectors in CR imaging.
The Imaging Plate	- The "cassette" which holds the Photostimulable Phosphor in digital imaging. - Looks much like screen film technology except that the Storage Phosphor Screen replaces the film and intensifying screens.
Cassette	Looks similar to film cassette but instead of housing film holds an imaging plate.
Protective Layer	Thin clear plastic that protects the phosphor layer.
Phosphor Layer	Holds the Photostimulable phosphor that "traps" electrons forming the latent image during exposure. Usually made of barium fluorohalide. May also contain a dye to prevent light spread.
Light Reflective Layer	Layer that sends light in a forward direction when released in the cassette reader.
Conductive Layer	Layer that absorbs and reduces static electricity. Acts as a ground.
Support Layer	A semi-rigid material that gives the imaging sheet some strength.
Light Shielding Layer	Prevents light from erasing data on the imaging plate or leaking through the backing,
Backing Layer	A soft polymer that protects the back of the cassette.
Barcode Label	Allows the technologist to match the image information with the patient-identifying barcode on the examination requested.
The storage phosphor screen or plate is housed inside of the ________________.	Imaging plate.
The Laser Beam	- A finely focused leaser beam(red light) frees trapped electrons in the phosphor layer of the imaging plate, referred to as photostimulated luminescence (PSL).
The Laser Beam:	- The laser beam scanning occurs in a raster pattern as the plate is fed through the processor. - Freeing these electrons causes a blue-purple light to be emitted.
Photomultiplier	Gathers the light from the SPS and converts it into an electronic signal which is in an analog form.
Analog to Digital Converter	Converts the analog signal from the photomultiplier into a digital signal.
Erasing the image	the residual image and any remaining trapped electrons are erased by exposure to an intense light.
Image Receptor Response Function	Similar to the D log E curve in film/screen technology ( will cover in RAD exposure).
Image Noise	- Deterioration of the radiographic image. - Mainly caused by scatter.
Contrast	In CR imaging, the concept that kVp controls contrast does not hold true for CR imaging. kVp and mAs only controls patient dose.
Erasing	- Exposing the Storage Phosphor Screen to bright white light to erase any latent image not sent to the reader. - If flooding of the phosphor plate was not performed, a ghost image would appear on the next image.
Detection (Reading) the stimulated emission	A photomultiplier tube (PMT) or a photodiode (PD) read the light emitted and produces a latent image in the form of an electronic signal.
Stimulation	- Those electrons who are still excited but trapped are released when exposed to a laser light (in the laser reader).
Stimulation:	- The trapped electrons release light when they are released by being exposed to a laser light. - Some of the image may be lost if processed longer than 8 hours after exposure.
Exposure to Radiation	- The Photostimulable Phosphor is exposed to radiation in the form of x-rays which allows the electrons in the Storage Phosphor Screen to become excited.
Exposure to Radiation:	- Some electrons are released immediately in the form of light (like traditional radiographic screens). - Other electrons remain and are released more slowly (CR imaging reader).
Light Stimulation Emission	1. Exposure to radiation. 2. Stimulation. 3. Detection (Reading) the stimulated emission. 4. Erasing.
Computed Radiography	Is a form of digital radiography.
With _____ a dark room is unnecessary.	CR.
The diameter of the laser beam determines the ___________ of the CR imaging system.	Spacial resolution.
_________ should be used soon after the erase cycle has been completed.	Imaging plates.
________ laser beam diameter is critical for ensuring high spatial resolution.	Small.
Sampling & Quantization	Are two processes of analog-to-digital conversion (ADC).
A _______ CR image has 16,384 gray levels.	14-bit.
_________ should be performed at lower techniques than screen-film radiography	CR.

Created by: sassyrad

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