Computed radiography, CR • Direct radiography or direct digital radiography, DR • Digital subtraction angiography, DSA
Computed Radiography (CR) is the generic term applied to an imaging system comprised of: ★Photostimulable Storage Phosphor to acquire the x-ray projection image ★CR Reader to extract the electronic latent image ★Digital electronics to convert the signals to digital form
Computed Radiography (CR) uses very similar equipment to conventional radiography except that in place of a film to create the image, an imaging plate (IP) is used. The imaging plate is placed under the object to be examined and the x-ray exposure is made.
X-rays Cassette Conventional radiography Screen-film combination IP only
CR Detector • Photostimulable Storage Phosphor (PSP) • BaFBr compound, Eu activated Phosphor Plate Or imaging plate”IP” Cassette Holder Barium fluorin bromide Eu: europium
instead of taking an exposed film into a darkroom for developing in chemical tanks or an automatic film processor, the imaging plate is run through a special laser scanner to read and digitize the image.
Computed Radiography “reader” Information panel Plate stacker
The CR imaging plate contains photostimulable storage phosphors, which store the radiation level received at each point in local electron energies. When the plate is put through the scanner, the scanning laser beam causes the electrons to relax to lower energy levels, emitting light that is detected by a photo-multiplier tube (PMT), which is then converted to an electronic signal.
The electronic signal is then converted to discrete (digital) values and placed into the image processor pixel map. • Imaging plates can theoretically be re-used thousands of times if they are handled carefully, although handling under industrial conditions may result in damage after a few hundred uses. An image can be erased by simply exposing the plate to a room-level fluorescent light.
The digital image can then be viewed and enhanced using software that has functions very similar to other conventional digital image-processing software, such as contrast, brightness, filtration and zoom.
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