AJR:196,June 2011
Yumi Yanaga, Kazuo Awai, Takeshi Nakaura, Daisuke Utsunomiya, Yoshinori Funama, Shuji Date, Yasuyuki Yamashita
OBJECTIVE. The purpose of this study was to compare the diagnostic capability of hepatic dynamic CT with low-dose contrast material (420 mg I/kg body weight) at 80 kVp with that of the same modality performed with standard-dose contrast material at 120 kVp.
SUBJECTS AND METHODS. We randomly assigned 111 patients (50 women, 61 men; mean age, 69.1 years) with known or suspected hepatocellular carcinoma and a body weight of 70 kg or less to one of two protocols. In the 80-kVp protocol, the contrast material (444 mg I/kg body weight) was delivered over 15 seconds at a tube voltage of 80 kVp. In the 120-kVp protocol, a contrast dose of 600 mg I/kg was delivered over 30 seconds at 120 kVp. Of the 111 patients, 38 had hypervascular hepatocellular carcinoma. Using the Mann-Whitney U test, we compared the two protocols for the contrast-to-noise ratio of the tumors (difference between tumor attenuation and liver attenuation divided by noise in the liver) and the figure of merit (square of contrast-to-noise ratio divided by effective dose) of the tumors during the arterial phase of imaging. Effective doses also were compared.
RESULTS. The contrast-to-noise ratio of the tumors was significantly higher with the 80-kVp than with the 120-kVp protocol (median, 5.3 vs 4.2; p = 0.04). The figure of merit also was significantly higher with the 80-kVp than with the 120-kVp protocol (10.2 vs 5.3, p = 0.02). The effective dose was significantly lower with the 80-kVp than with the 120-kVp protocol (2.97 vs 3.41 mSv, p < 0.01).
CONCLUSION. With 80-kVp acquisition, the contrast-to-noise ratio and figure of merit of tumors during the arterial phase improved despite the lower contrast dose and radiation exposure.