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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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