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Digital Radiography: CCDs Deserve Another Look
Image sensors are playing a more vital role
By Keith Wetzel, Eastman Kodak Company
At a time when hospitals are under increasing pressure to lower costs, digital radiography promises to transform diagnostic imaging by improving operating efficiencies and speeding patient throughput. In addition, capturing images electronically eliminates the materials and processing costs associated with X-ray film and, by producing immediate results, it also decreases the need for redundant images.
Early digital radiography camera systems used commercial charge coupled devices (CCDs) to capture X-ray images produced on a scintillation screen. In these systems (see Figure 1), X-rays passing through a patient impinge upon the scintillator screen to emit an image, which a mirror/lens assembly projects onto a CCD. The CCD captures the image by converting visible light into electrons that are subsequently stored within the CCD pixels.
While the image quality achieved by these early systems was sufficient to gain market acceptance, users desired better image quality and lower X-ray doses. Because CCDs are typically small in size relative to a 17” x 17” scintillation screen, they often require substantial demagnification of the image, leading some experts to express concern that the sensitivity of CCD cameras was not sufficient to compensate for light lost through the lens assembly. This light loss was seen as an insolvable problem and CCD camera technology was largely dismissed as a viable long-term option for use in digital radiography. At the same time, several major suppliers began promoting the use of flat panel detectors — based either on amorphous silicon or amorphous selenium — as a competing solution for digital X-ray image capture.