Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

the faces of the monitors, and to avoid reflections on the monitor's faces frombright objects. Viewing conditions are more important when monitors are usedthan when viewboxes are used, because of the lower luminance of the monitors.The room should have adjustable indirect lighting and should not have windowsunless they can be blocked with opaque curtains or shutters. When more than oneworkstation is in a room, provisions should be made, either by monitor placementor by the use of partitions, to prevent the monitots from casting reflections on eachother. Particular care must be taken, if both conventional viewboxes and workstationsare used in the same room, to prevent the viewboxes from casting reflectionson monitor screens and impairing the adaptation of physicians' eyes to the dimmermonitors.HardcopyDevicesHardcopy devices permit the recording of digital images on photographic film.These devices usually provide several formats (e.g., four images per sheet, six imagesper sheet). Two devices for recording images on film are multiformat video camerasand laser cameras.Multiformat Video CameraA multiformat video camera consists of a high-quality video monitor; one or morecamera lenses, each with an electrically-controlled shutter; and a holder for a cassettecontaining a sheet of photographic film, all in a light-tight enclosure (Fig. 17-11). The size and position of each image on the film is adjusted by moving the lens,in a single-lens system; by using different lenses, in a multiple-lens system; or by acombination of the two. A multiformat video camera is usually provided an analogvideo signal from a video card on an image processing workstation, and the formatis manually selected by a technologist operating the camera. The spatial resolutionand contrast of the video monitor limit the quality of the recorded images from amultiformat video camera.Laser Multiformat CameraA film laser camera consists of a laser with a modulatot to vary the intensity of thebeam; a rotating polygonal mirror to scan the laser beam across the film; and a filmtransportmechanism to move the film in a lineat fashion so that the scanningoptical lensand shutter------~....-_...-.FIGURE 17-11. Multiformat videocamera.