CCD film digitizers in clinical practice: evaluation of the main properties

Until hospitals convert to 'filmless' radiology departments, computerized display and archival of x-ray images will necessitate devices to transform conventional X-ray films into digital images. Current methods for digitizing x-ray films include laser based and Charged Couple Device (CCD) based scanners. There is now much interest in the use of CCD devices for demanding applications, with the lower cost of ownership contributing towards the diffusion of CCD scanners. We report a study comparing the performance of three CCD based systems (an x-ray film digitizer, and two low cost flatbed scanners), looking at characteristic curve, useful optical range with respect to the noise, repeatability, Modulation Transfer Function (MTF), and geometric distortion. In addition, we evaluated the potential and limitations of these devices in the clinical assessment of x-ray films. The most important weakness of CCD devices derived from the stability and the noise of CCD detectors, mostly affecting the useful optical range in the darker regions of x-ray films. Spatial resolution and geometric distortion were confirmed to be the real points of strength of CCD technology. Therefore, the most appropriate system for each user depends on what type of clinical decision will be made following inspection of the digitised images.