[Simple method of setting proper exposure in X-ray CT examination of head and abdomen]

In abdominal X-ray computerized tomography (CT) , exposure conditions can be established by real-time exposure control and manual procedures, depending on the body type. In the former, appropriate dose control can be attained. In the latter, dose cannot be controlled to a very precise level, since the dose is controlled manually, according to body type. In head X-ray CT, the conditions are in most cases established manually. We determined the causal relationship between the body mass index (BMI) showing the body type of a subject and the abdominal cross section/circumferential length of the subject. Then a water phantom that simulated the abdominal area was used to take pictures, with the current time integrator changed, relating the section area and circumferential length of the water phantom with the body mass index, thereby determining the relationship with the current time integrator. Further, a water phantom simulating the head was used to take pictures, with the current time integrator changed, thereby determining the relationship between the circumferential length of the water phantom with the current time integrator. We determined that pictures can be taken at a dose that is close to an appropriate dose, when these relationships are plotted to determine the standard deviation (SD) for establishing exposure conditions.