说明：  医疗数字图像处理基础 医疗数字图像、数字图像处理
(There was a time not so long ago, well within the memory of many of us, when medical imaging was an analog process in which X-rays, or reflected ultrasound signals, exiting from a patient were intercepted by a detector, and their intensity depicted as bright spots on a fluorescent screen or dark areas in a photographic film. The linkage between the exiting radiation and the resulting image was direct, and the process of forming the image was easily understandable and controllable.)