Exposure dose in CT with special reference to exposure in CT-H 250

Exposure in a computed tomography, Hitachi CT-H 250 type, was discussed. Circumferential dose was measured by using elliptoidal phantoms (19 x 12, 12 x 11 cm) of Mix Dp. The maximum exposure dose by the large phantom was 2.9 rad and minimum dose was 0.23 rad. The maximum dose measured by the small phantom which was used by supposing the head of infants was 2.2 rad and the minimum dose was the same as that by the large phantom. Exposure dose out of flux (the neck, the abdomen, etc.), volume dose, and distribution of scattered x-ray in a room were also discussed. When an adaptor which restrained infant head was manufactured for trial, decrease of exposure dose was attempted by photographing with low voltage in a tube. Exposure dose was measured by the small phantom with low voltage of 120 kv, 100 kv, and 96 kv. As a result, the maximum dose of exposure decreased from 1740 to 1085 and 850 R which was under 50% of the first measurement value. There was not a significant difference in CT values and photographed pictures. (Serizawa, K.)