Current radiographs were compared with previous ones, and their anomalies were enhanced by the digital subtraction of both images. This procedure affords easy recognition of temporal changes. The image by which the first derivative filter limits the orientation of gradients was used in order for "lung markings" to be matched when making adjustments prior to the subtraction of the two images. Previous and current images were then matched using the sequential similarity detection algorithm (SSDA) method. With our method, Althougy artifacts due to disagreement of the costal shadow were generated, subtle opacities such as infiltrates, nodules, bands, linear shadows, and cardiomegaly were clearly enhanced on the subtraction image. This suggests improved accuracy when fadiologists diagnose a sepuential chest image using the subtraction image.

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The technique of interventional radiology has spread rapidly in recent years, and three-dimensional information from blood vessel images is being sought to enhance examinations. Stereo digital subtraction angiography (DSA) and rotational DSA were developed for that purpose. However, it is difficult with sterel DSA to observe the image pair during examination and to obtain positional information on blood vessels. Further, the exposure dose is increased in rotational DSA when many mask images need to be collected, and the patient is required to hold his or her breath for a long duration. We therefore devised an technique to construct three-dimensional blood vessel images by employing geometrical imformation extracted from stereo DSA images using the right and left images. We used a judgment method based on the correlation coefficient, although we had to extract an equal blood vessel from the right and left images to determine the three-dimensional coordinates of the blood vessel. The reconstructed three-dimansional blood vessels were profected from various angles, again by using a virtual focus, and new images were created. These image groups were displayed as rotational images by the animation display function incorporated in the DSA device. This system can observe blood vessel images of the same phase an a free angle, althougy the image quality is inferiour to that of rotational DSA. In addition, because collection of the mask images is reduced, exposure dose can be decreased. Further, the system offers enhanced safety because no mechanical movement of the imaging system is involved

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Radiographic conditions (x-ray tube voltage, irradiation time, etc.) differ among medical facilities. A second questionnaires was sent out to determine the current state of pediatric radiography and eventually provide reference materials for the standardization of radiographic parameters used in pediatric x-ray examinations. The questionnaire, which was sent in 1996, targeted 161 facilities that belong to the Society for Pediatric Radiological Technology. The objects of examination were the chest, upper airway, abdomen, hip joint, skull, and knee joint. The questionnaire investigated age (children of six months, three years, and seven years), type of x-ray generator, radiographic conditions, etc. Moreover, this time the items head x-ray computed tomography (X-CT) and abdominal X-CT were added. Completed questionnaires were received from 79 facilities, for a recovery of 49.1%. Compared with the previous investigation, inverter-type high-voltage assemblies increased, whereas twelve-peak high-voltage assemblies decreased. The focal spot of the x-ray tube assembly was smaller, and maximum anode heat content had increased. CR systems and green luminescenceorthochromatic systems were increasingly being used as image receptors. Advances in x-ray generators and the image receptor systems created reductions in the time required for radiography, which was possible at as short a time as 1 msec. Moreover, image quality was also improved by these advances. However, no major changes were observed in the conditions of radiography.

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