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Radiation Dose Reduction without Degradation of Low-Contrast Detectability at Abdominal Multisection CT with a Low–Tube Voltage Technique: Phantom Study¹

¹ From the Department of Radiological Sciences, School of Health Sciences (Y.F., M.S.), and Department of Diagnostic Radiology, Graduate School of Medical Sciences (K.A., Y.N., S.S., S.M., Y.Y.), Kumamoto University, 4.24.1 Kuhonji, Kumamoto 862-0976, Japan; Department of Radiology, Kumamoto University Hospital, Kumamoto, Japan (K.K., N.N.); and Philips Medical Systems, Minato-ku, Tokyo, Japan (N.S.). Received September 23, 2004; revision requested November 30; revision received January 23, 2005; accepted February 23. Address correspondence to Y.F.

PURPOSE: To reduce radiation dose from 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 test, 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 were measured. To assess low-contrast detectability, we used a 300-mAs setting at 120 kV and 250–560-mAs settings at 90 kV. Five observers participated in the receiver operating characteristic analysis. Area under the receiver operating characteristic curve (A_z) values were calculated in each observer. A_z values obtained with each of the scanning techniques were recorded, and differences were examined for significance by using the Dunnet method.

RESULTS: The mean A_z value was 0.951 at 120 kV and 300 mAs. A_z 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 of 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.

© RSNA, 2005

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