[en] We reported a new device of phantom type compensating filters for pulmonary hilar tomography with polytome U at the 35th annual meeting of the Japanese Society of Radiological Technology. This report is to show application of this compensated method to the head, the hip joint and the lower thoracic spine in tomography. Using the filters optimal density can be obtained in all area of aim part on a X-ray film, and thus makes to get more information. 1) In the head clear shadow of pars nasalis, sinus paranasales and sella turcica is obtained. Destruction or defect of bone contour is easily detected. It is also useful to differentiate the disorders and to determine the expansivity of the lesion. 2) In the hip joint this method has advantages over the ordinary method. There is a few misdiagnosis in trochanteric lesions such as tuberculosis or bone tumor, because of high density at the trochanteric region in ordinary method, but in this method optimal density can be obtained, and misdiagnosis is improved. Soft tissue is sharply visualized, indicating usefulness in diagnosis of existence of hematoma or abscess. 3) In the lower thoracic vertebra it is useful to diagnosis of the thoracic spondylosis, tuberculous spondylitis and compression fracture of the vertebral body, since optimal density of the spine can be obtained. It is also quite useful to detect small ossifications in the vertebral foraman in ossification of the flavum ligament. (author)

[en] In the case of chest tomography, particularly the mediastinum and the pulmonary hilar tomography are difficult to argue the matter without the exposure time factor. For that reason, these regions are much used rectilinear tomography for the shortening of the exposure time. However as for visualities of form, it is advisable for these regions to be used in multidirectional tomography. However, a longer exposure time is needed. Therefore, we experienced with stereozonography with a shorter exposure time by circuler direction using compensating filter and computed radiography. Shifting distance of X-ray tube for stereography was 10% of distance between the focal spot and object. The exposure time and exposure angle were 0.6 sec and 2θ=3deg, respectively. As a result, this stereozonography was excellent in the visuabilities of the mediastinal region, including bronchovascular shadows, allowing a detailed examination of the on images of these region. Compensating filter permitted improved image quality of the mediastinal region. On the other hand, using the computed radiographic system, even if an artifact arose from disagreement between the form of the compensating filter and the mediastinal region, we could easily restore the nondiagnostic image by overall density manipulation and unsharp mask filtering. (author)

[en] A compensating filter has been employed for hilar tomography in over 1,200 cases. The visuability of bronchovascular shadows using the filtered tomography was analyzed. The filtered tomograms clearly showed a bronchial tree from the carina to the proximal portion of the lower lobe bronchus in over 95% of the cases examined, except for unfavorable cases due to overlapping lesions. However, as for the left lower region compared with the other regions, the visuability of the anatomical architecture decreased because of the inappropriate shape of the filter and as a result of technical errors. Next, the previous straight type of filter was reshaped so as to be adapt able to the mediastinal structure. As a result, the newly reformed filter improved the visuability of the distal portion of the lower lobe bronchus, central part of left lower vein, and its peripheral part by 23.9%, 5%, and 17.0%, respectively, compared with the previous filter, and reduced the amount of technical errors. (author)

[en] The detectability of simulated low-contrast objects in CT images on a CRT were investigated. The limits of the detection of a signal (i.e., a disease) were discussed in terms of CRT diagnosis. Assuming that the CT images were observed on a CRT exposed with an abdominal condition, this experiment was performed. The 16-alternative forced-choice (16-AFC) experiments was employed to study the dependence of the detectability of test objects regarding objects size (0.25∼9 cm²), background noise level (RMS=20.6, 10.3, 5.7) and objects contrast (-1∼-16 CT numbers). The CT images were displayed on a 735-line CRT (12-inch, interlaced, 256 gray levels). The results indicate that the detectability of low-contrast objects in the CT images on a CRT depends strongly on the background noise level and object size. When the RMS noise level was higher than 10 or the object size smaller than 1 cm², the detectability decreased sharply. Through these results the limits of the detection of a signal in terms of CRT diagnosis could be observed. (author)

[en] The absorption coefficient of the living body can be indicated by CT numbers. Then, we made up low absorption test charts on equal terms with the living body, and studied the relationship between CT numbers and interval factors in conventional tomography. The visual interval factor changes according to the CT number. The interval factor changes to a great extent with a CT number of less than 500, and to a small extent with numbers of 1000 on over. It is inferred that the interval factors measured in present study are similar in value for them in clinical tomogram. (author)

[en] In the case of chest tomography, particularly the mediastinum and the pulmonary hilar tomography are difficult to the matter without exposure time factor. For the reason, these regions are much used rectilinear tomography for the shortening of the exposure time. But, as for the visuability of the morphology, it is advisable for these regions to use in multi-directional tomography. However, it is in need of long exposure time. Therefore, authors experimented with stereozonography of short exposure time by circular movement using a compensating filter and computed radiography. Shifting distance of X-ray tube for stereography was 10% of distance between focus and object. The exposure time and exposure angle were 0.6 sec, 2θ = 3 deg, respectively. As a result, this stereozonography was excellent in the visuability of mediastinal region, including bronchovascular shadows, and could examine in details is on images of these region. By using the compensating filter, the improved image quality of mediastinal region was obtained. In addition, using computed radiographic system, even if artifact araised from disagreement between form of the compensating filter and mediastinal region, authors could easily restored non-diagnostic image by overall density manipulation and unsharp mark filtering. (author)