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.
