07 Computed Radiography 3-30-21 (1).pdf

Computed Radiography Digital Radiography: Term that includes both computed radiography (CR) and direct radiography (DR). Digital radiography entered the medical field in the 1970s with the advent of computed tomography (CT) & digital subtraction angiography (DSA). Computed Radiography (CR): Cassette...

Computed Radiography Digital Radiography: Term that includes both computed radiography (CR) and direct radiography (DR). Digital radiography entered the medical field in the 1970s with the advent of computed tomography (CT) & digital subtraction angiography (DSA). Computed Radiography (CR): Cassette-based digital radiography. Fuji introduced the first CR systems in the US in 1983. Did not take off until the 1990s. Computed Radiography (CR): CR is a marketing term for photostimulable phosphor (PSP) detector systems. An analog signal (data) is created and interpreted by analog and digital devices. As the exit beam strikes these phosphors, some light is emitted but most of the energy is trapped in the PSP screen. PSP screens are sometimes called storage phosphors or imaging plates. CR Imaging Plates: They are made of barium fluorohalide crystals. 85% BaFBr and 15% BaFI. CR Imaging Plates: CR imaging plates are activated by a small quantity of europium. Europium doping creates defects in the barium fluorohalide crystals. Following exposure to the exit beam, these defects provide an efficient means to trap electrons at a different energy level. CR Imaging Plate & Cassette: CR Reader: CR Reader: Scanning the Imaging Plate: Digitized Signal CR Reader Workstation CR Processing: Following exposure to the exit beam, a latent image is formed on the CR plate. The cassette is placed in a CR reader and the plate is removed. It is then scanned by a high-intensity laser beam (red light). The laser stimulates the movement of some of the trapped electrons back to their original position. CR Processing: As this occurs, there is an emission of a bluegreen light from the CR plate. This process is called light-stimulated phosphorescence. The blue-green light is collected by a fiber optic light guide and sent to a PMT where an electronic signal is generated. The red laser light is filtered out and removed. CR Processing: Analog-to-digital Converter (ADC) Converts the electric signal from the PMT into a digital signal. Workstation Allows for post processing image manipulation. Final images are sent to PACS. Clearing the CR Plate: Exposure to the laser beam will not “reset” all of the electrons within the CR plate back to their original position. It must be exposed to a bright white light to remove any residual energy prior to returning to the cassette. If this does not occur, a ghost image will remain on the CR plate. Ghost Image: Ghost Image: Ghost Image: CR Sensitivity to Noise: Imaging plates are very sensitive to background and scatter radiation. They should be erased after 48 hours of nonuse. CR vs. Background Radiation: Erased Cassette CR vs. Background Radiation: One Week CR vs. Scatter Radiation: CR Collimation Considerations: If the collimated borders are not recognized, the image data analysis will include all of the data outside the collimation. The final image may not have the correct level of brightness and contrast. Tightly collimated images should be placed in the center of the IR. Exposure Indicators vs. mAs (x): Fuji/Konica Minolta/ Siemans/Philips GE/Agfa Kodak/Carestream Symbol ½(x) Perfect (x) 2(x) S# 400 200 100 lgM 1.9 2.2 2.5 EI 1700 2000 2300 This is our goal…ALARA. mAs vs. Konica Minolta S#: 60 kVp @ 2 mAs 60 kVp @ 4 mAs 60 kVp @ 8 mAs S# 397 S# 201 S# 98 Which of these images would be most ideal?