PURPOSE: To reduce radiation dose (rom abdominal computed tomography (CT) without degradation of low-contrast detectability by using a technique with low tube voltage (90 kV).
MATERIALS AND METHODS: The institutional review board approved the participation of the radiologists in the observer performance lest, and informed consent was obtained from all participating radiologists. A phantom for measurement of the radiation dose and a phantom containing low-contrast objects were scanned with a 16-detector row CT scanner at 120 kV and 90 kV. For determination of the radiation dose at both 90 kV and 120 kV, the tube current-time product settings were 100-560 mAs, and the doses at the center and periphery of the phantom wpre measured. To assess low-contrast detectability, we used a 300-mAs setting at 120 kV and 250 560-mAs settings at 90 kV. Hvc observers participated in the receiver operating characteristic analysis. Area under the receiver operating characteristic curve (A,) values were calculated in each observer. Az values obtained with each of the scanning techniques were recorded, and differences were examined for significance by using the Dunnet method.
RESULTS: The mean Az value was 0.951 at 120 kV and 300 mAs. Az values were 0.927-0.973 at 90 kV and 450-560 mAs, and the differences between those values and values obtained at 120 kV and 300 mAs were not significant (P = .937-.952). A value ot 100% was assigned to the radiation dose delivered to the center of the phantom at 120 kV and 300 mAs. The relative dose delivered at 90 kV ranged from 65% at 450 mAs to 79% at 560 mAs.
CONCLUSION: A reduction from 120 kV to 90 kV led to as much as a 35% reduction in the radiation dose, without sacrifice of low-contrast detectability, at CT.