We investigated the photo graphic properties of hypersensitized X-ray films during short exposure, which were treated with forming gas, by comparing their speeds, H&D curves gradients with those of untreated X-ray films. The relative speeds of treated films to untreated films were 1.5〜2.5 times (D=1.0), but some of the treated films yielded high fog levels and decreased gradients compared to the untreated X-ray films. Form our experimental results, it is considered that the hypersensitization technique by forming gas might be employed for diagnostic purpose to reduce the patient exposure by approximately 30〜60%.
Threshold contrasts of four digital subtraction angiography (DSA) systems were compared using a contrast-detail (C-D) phantom which can be used for the measurement of quantitative C-D diagrams. The C-D diagrams were determined form an observer performance study and were plotted on log-log curves for comparison of threshold contrast of the simulated vessels. The results indicated that the threshold contrast of DSA systems decreased by increasing the incident exposure to the image intensifier (I.I.). The slopes of the curves for three DSA systems were similar. However, one DSA system indicated a different slope. This is assumed that the artifacts in the subtracted image disturbed the appearance of the simulated vessels.
Recently, in addition to the method for evaluating physically the quality of radiographic images, the method of psycological estimate has been proposed. It has been standard practice in which the final evaluation of radiographic images have been carried out by human vision. For this reason, we are not able to understand the process and references used in a physical evaluation. So we evaluated the Thurstone's Method of Paired Comparisons as a method of evaluating the plain skull radiographs, and have produced a scale. We evaluated sharpness, granularity, contrast, etc. and so the total image quality of plain skull radiographs. It indicated a strong relationship between total evaluation and sharpness of the plain skull radiographs. Since the preference value of the observer was able to be analyzed quantitatively by using the Thurstone method, it was possible to do a subjective evaluation of image quality on an interval scale. Thus, the analysis based on the interval scale was verified to be useful for a total evaluation.
To determine a treatment field for radiation therapy, a conventional X-ray simulator has been used so far. However, exact extension of the tumor can not be obtained by a conventional X-ray simulator, and, it is often difficult to simulate the treatment field obtained by CT on a conventional X-ray simulator. We have developed a method to produce a beam's eye projection through axial CT data, which has an identical geometrical location as verification film taken by the anticipated treatment beam called process Computed Simulationgraphy. The process and image enable treatment planning, making the treatment field on the patient's skin and verifying the port film.
It is still usually necessary for patients with spina bifida to take lumbo-sacral vertebral tomograms at our hospital. However it is impossible to visualized the whole region in one film in the spine position, because the long axis of the lumbo-sacral vertebrae is not parallel to the film. We measured the angle between the table and line passing through lumbo-sacral joint and third-forth sacral joint on the lumbo-sacral lateral X-ray photograms. So, we tried to make a supplementary table to change the region parallel to the film and attempted to apply the table to some clinical cases. As result, the tomograms with the supplementary table were seen as being more useful, because the whole lumbo-sacral region is visualized in one film.
Screen speeds, modulation transfer functions (MTFs), and Wiener Spectra of conventional and reduced crossover screens were measured in the evaluation of the physical properties of anti-crossover system. The relative speeds of reduced crossover screens were comparable to those of conventional screens. The reduced crossover screens improved resolution properties slightiy. Noise properties of the reduced crossover screens were comparable to or slightly lower than those of the conventional screens. Radiographs of the hands indicated that reduced crossover screens could improve image quality factor over conventional screens.
There is no compareble method of dose specification which is enable to adopt in any centers but it is important to define the method, to mantaine the treatment palicy and to compare the results of treatments with those of the other centers. Even if there are some questions between the recomendations in ICRU-29 and present method in several institutes, there are substantial advantages in taking a common methods of ICRU-29.