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Abdominal CT with Low Tube Voltage: Preliminary Observations about Radiation Dose, Contrast Enhancement, Image Quality, and Noise¹

¹ From the Department of Diagnostic Radiology, Graduate School of Medical Sciences (Y.N., K.A., M.H., M.I., T.N., D.R., S.M., S.S., Y.Y.), and Department of Radiological Sciences, School of Health Sciences (Y.F.), Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan; and Philips Medical Systems, Minato-ku, Tokyo, Japan (N.S.). Received September 26, 2004; revision requested November 30; revision received February 12, 2005; accepted March 8. Address correspondence to Y.N.

View larger version (23K): [in a new window]   Figure 1. Graph shows that the mean CT number of test tubes of the phantom that were scanned at 120 kV and 90 kV increases with increasing iodine concentrations. There was a significant linear correlation between the CT number and the iodine concentration (r = 0.999, P < .001). Higher CT numbers were obtained at 90 kV than at 120 kV.

View larger version (122K): [in a new window]   Figure 2a. Transverse CT images obtained for screening for hepatocellular carcinoma in a 56-year-old man with chronic hepatic disease who weighed 62 kg. (a) Scan obtained in early arterial phase with protocol A (120 kV, 300 mAs, and 100 mL of contrast material). (b) Corresponding image acquired with protocol C (90 kV, 300 mAs, and 80 mL of contrast material) 2 weeks after the initial scan was obtained with 120 kV. The window setting is optimized at a window width of 300 HU and a window level of 50 HU in both images. The CT number of the aorta at 90 kV was higher than that at 120 kV (334 HU and 237 HU, respectively), although the image noise was more prominent on b than on a (19.4 HU vs 13.1 HU).

View larger version (121K): [in a new window]   Figure 2b. Transverse CT images obtained for screening for hepatocellular carcinoma in a 56-year-old man with chronic hepatic disease who weighed 62 kg. (a) Scan obtained in early arterial phase with protocol A (120 kV, 300 mAs, and 100 mL of contrast material). (b) Corresponding image acquired with protocol C (90 kV, 300 mAs, and 80 mL of contrast material) 2 weeks after the initial scan was obtained with 120 kV. The window setting is optimized at a window width of 300 HU and a window level of 50 HU in both images. The CT number of the aorta at 90 kV was higher than that at 120 kV (334 HU and 237 HU, respectively), although the image noise was more prominent on b than on a (19.4 HU vs 13.1 HU).

View larger version (19K): [in a new window]   Figure 3. Scatterplot shows the relationship between SNR of the aorta and the patient's body weight in the early arterial phase with protocols A and B. CM = contrast material.

View larger version (19K): [in a new window]   Figure 4. Scatterplot shows the relationship between SNR of the liver and the patient's body weight in the delayed arterial phase with protocols A and B. CM = contrast material.