Radiographic apparatus and method with logarithmic video compression

摘要

A source of radiation irradiates an area of interest of a patient. An image intensifier receives the x-rays which have traversed the patient and provides an optical image of an x-ray shadowgraph through the examined area of the patient. A television camera converts the optical image into a video signal. A signal processor operates on the video signal by adding an offset signal to the gray scale signal and by logarithmically compressing the gray scale portion of the video signal. An automatic zero circuit is provided which readjusts the offset signal between each horizontal sweep of the television camera. The logarithmically compressed gray scale portion of the video signal and the synchronization portion are received by an image processor. The image processor digitally stores a mask image or shadowgraph of the patient before being injected with an x-ray opaque contrast agent. The image processor also stores in a post contrast image or shadowgraph of the same area of the patient after the patient has been injected with an x-ray opaque contrast agent. The image processor subtractively combines the mask image with the post contrast image to produce a difference image. A video monitor displays the difference image.