The digital mammography system evaluated here is a digital full-field phase contrast mammography (PCM) system that employs a practical molybdenum x-ray tube with a 0.1mm focal spot size. By using custom apparatus to position 14"x17" photostimulable phosphor plate 49cm from the object, a distance of 65cm was obtained between the object and the focal spot of the x-ray tube. A plate optimized for the PCM system acquired images magnified 1.75 times with a 14"x17" and was scanned at a sampling pitch of 43.75μm by using a CR system. The diagnostic images were reduced in printing to actual object size with a pixel size of 25μm on 8"x10" dry-processed film with a maximum density of 4. This study compares the performance of the system with that of a usual contact CR mammography system.
In x-ray radiographs for use in the medical field, it is desired that the density in the region of interest (ROI, area containing important image consistent for diagnosis) on the x-ray radiograph image is stable and its gradation is adjusted so that the structure of human body and the shade and shadow of the lesion can be observed easily. In developing the Konica Direct Digitizer, which is a digital radiographic image input apparatus to be used exclusively for chest and abdomen images, we have developed a new automatic gray scale transformation algorithm capable of providing most suitable images for diagnosis. The remarkable characteristic of the automatic gray scale transformation algorithm developed this time is to identify automatically the position of ROI in the image and to determine the gray scale transformation conditions based on the image data in the ROI. We investigated 50 clinical images radiographed by Konica Direct Digitizer from the viewpoint of the accuracy of the position of ROI established by the automatic gray scale transformation and of the image finish conditions accomplished by the automatic gray scale transformation. As a result, we have learned that both of them were stable and sufficiently accurate. From now on, we further improve its accuracy by increasing clinical images and applying this system to various regions.