 Computed Radiography (CR) Definitions and Terminology
Computed Radiography (CR) Terminology and Definitions
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) made of photostimulable phosphor is used. The imaging plate housed in a special cassette and placed under the body part or object to be examined and the x-ray exposure is made. Hence, 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, or CR reader, that reads and digitizes the image. 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. Differences from Direct Radiography CR and DR should not be confused with Fluoroscopy, where there is a continuous beam of radiation, and the images appear on the screen like on a TV. This is the system many people are familiar with, where the image of the article being x-rayed is viewed in real time on a monitor or display. Many people think airports use Fluoroscopes for baggage inspection, when in fact LDA's (Linear Diode Arrays) are universally used to generate static images of luggage content. LDA's are also used in a wide variety of other screening and imaging applications, and are also presented in a digital format. Modern fluorosopes use a device called an image intensifier to enhance the analog output of the real time x-ray image, where it is picked up by either a video or CCD camera and digitally enhanced to reduce the noise inherent in the system. Imaging plateThe CR imaging plate (IP) 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, 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. IP handling under industrial conditions, however, 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. Most laser scanners automatically erase the image plate after laser scanning is complete. The imaging plate can then be re-used. Reusable phosphor plates are environmentally safe but need to be disposed of according to local regulations. Industrial applicationsCommon applications for computed radiography include: corrosion surveys on pipes, often through insulation; AdvantagesNo silver based film or chemicals are required to process film. Products Referenceshttp://www.icrcompany.com/ |
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