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Hypervascular Liver Tumors: Low Tube Voltage, High Tube Current Multi–Detector Row CT for Enhanced Detection—Phantom Study¹

¹ From the Department of Radiology (S.T.S., R.C.N., S.M., E.K.P., T.A.J., C.M.M., D.M.D., K.K., T.T.Y., E.S.) and Division of Radiation Safety (T.T.Y.), Duke University Medical Center, Box 3808, Erwin Rd, Durham, NC 27710; and Department of Biomedical Engineering, Duke University, Durham, NC (S.M., K.K., E.S.). Received February 14, 2007; revision requested April 24; revision received May 15; final version accepted June 25. Address correspondence to R.C.N. (e-mail: rendon.nelson{at}duke.edu).

Purpose: To prospectively evaluate, for the depiction of simulated hypervascular liver lesions in a phantom, the effect of a low tube voltage, high tube current computed tomographic (CT) technique on image noise, contrast-to-noise ratio (CNR), lesion conspicuity, and radiation dose.

Materials and Methods: A custom liver phantom containing 16 cylindric cavities (four cavities each of 3, 5, 8, and 15 mm in diameter) filled with various iodinated solutions to simulate hypervascular liver lesions was scanned with a 64-section multi–detector row CT scanner at 140, 120, 100, and 80 kVp, with corresponding tube current–time product settings at 225, 275, 420, and 675 mAs, respectively. The CNRs for six simulated lesions filled with different iodinated solutions were calculated. A figure of merit (FOM) for each lesion was computed as the ratio of CNR² to effective dose (ED). Three radiologists independently graded the conspicuity of 16 simulated lesions. An anthropomorphic phantom was scanned to evaluate the ED. Statistical analysis included one-way analysis of variance.

Results: Image noise increased by 45% with the 80-kVp protocol compared with the 140-kVp protocol (P < .001). However, the lowest ED and the highest CNR were achieved with the 80-kVp protocol. The FOM results indicated that at a constant ED, a reduction of tube voltage from 140 to 120, 100, and 80 kVp increased the CNR by factors of at least 1.6, 2.4, and 3.6, respectively (P < .001). At a constant CNR, corresponding reductions in ED were by a factor of 2.5, 5.5, and 12.7, respectively (P < .001). The highest lesion conspicuity was achieved with the 80-kVp protocol.

Conclusion: The CNR of simulated hypervascular liver lesions can be substantially increased and the radiation dose reduced by using an 80-kVp, high tube current CT technique.

© RSNA, 2007