Japanese Journal of Radiological Technology

The selection of a suitable intensifying metallic plate is an important problem in improving the quality of images of linacography(LG) using computed radiography(CR). We examined a heavy metallic sheet(HMS:Sumitomo Electronic Engineering Co.Inc.) and copper(Cu) plate as devices for the intensification and elimination of scattered x-rays by comparing the quality of CR images. Results showed that the HMS had better selectivity, a higher contrast improvement factor and greater removal of scattered x-rays than the copper plate because of its high linear attenuation coefficient. It was also shown that, because of the flexibility and elasticity of the HMS, it could be in closer contact with the imaging plate(IP) without cousing damage. To increase the syapness of CR images, the HMS should be used instead of a copper plate, and it should be used with the cassette developed by Sato et al.(1997)

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It is not easy to demonstrate the fine structure of human bones like the stapes and long process of the incus with three-dimensional(3-D)images using helical CT. In this study, fine structural imaging of the normal ossicular chain was investigated using helical CT with virtual endoscopy(VE). In cases of normal hearing, axial helical CT of the temporal bones was performed with a GE HSA. The endoscopic views were produced with commercially available software. VE images were studied with different threshold settings, and the measured CT values of these structures(incus long process, stapes crus)tended to vanish at various threshold settings(-800 to 0 H.U.). Accurate VE images of the assicular chain could be obtained at a threshold setting of about -600 H.U.. Furthermore, three elements of the superstructure of the stapes(two cruses and a head) were separately visualized with VE images using helical CT in 93.3% of all ears. Although VE using helical CT has some limitations at this time, this procedure when used for ossicular chain imaging in patients with ossicular lesions may provide important information for imaging diagnosis and preoperative planning. The combination of axial images and VE could be useful for ossicular chain abnormalities.

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The number of deaths due to lung cancer has been increasing in Japan. The ability to detect lung cancer in its early stage using conventional chest radiographs unfortunately is limited. However, helical computed tomography(CT), which is able to scan the entire lung in a single breath-hold, offers excellent image contrast resolution. We therefore introduced a mobile helical CT unit with a dieselized electric generator into our lung cancer screening programs. Helical CT images were obtained under the following scanning conditions: 120 kV, 140 mA, 10 mm slice-thickness, and 20 mm/2 sec/rotation, with a 10 mm reconstruction increment. Scanninng the entire lung in a single breath-hold, the average breath-hold time required for males was 30 seconds and that for females 26 seconds. In our vehicle, the CT unit is set up in an examination room that is directly adjacent to the room where the generator is located. When vibration and noise levels were measured in the examination room(using vibrator and sound detectors), the bed vibration and noise level caused by the generator were determined to be 22.5 gal and 70.8 dB, respectively. Using the commercial external electric power supply(3 phase, 200 V) to the CT unit, the vibration and noise level on the bed were 2.94 gal and 68.8 dB, respectively. The vibration level caused by the generator was 7.7 times greater than that caused by the external power supply. When used under actual conditions, however, the resolution and contrast of the images provided power supply. When used under actual conditions, however, the resolution and contrast of the images provided by the generator showed no difference compared with those provided by the external power supply.

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