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Abdominal Multidetector CT in Patients with Varying Body Fat Percentages: Estimation of Optimal Contrast Material Dose¹

¹ From the Department of Radiology, Kizawa Memorial Hospital, Gifu, Japan (H.K., Y.T.); Departments of Radiology (H.K., M.K., S.G.), Radiology Services (M.K., T.M.), and Medical Informatics (Y.S.), Gifu University Hospital, 1-1 Yanagido, Gifu 501-1194, Japan; Research Center of Brain and Oral Science (M.K., M.O.) and Department of Physiology and Neuroscience (M.O.), Kanagawa Dental College, Yokosuka, Japan; Department of Radiology, Nagano Red Cross Hospital, Nagano, Japan (A.H.); Research Center for Cancer Prevention and Screening, National Cancer Center Hospital, Tsukiji, Japan (N.M.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (K.T.B.). Received January 5, 2008; revision requested February 26; revision received March 26; final version accepted June 23. Supported in part by the Grant for Scientific Research Expenses for Health, Labor, and Welfare Programs; Foundation for the Promotion of Cancer Research; and Research on Cancer Prevention and Health Services. Address correspondence to H.K.

Purpose: To determine if contrast material dose for abdominal multidetector computed tomography (CT), as determined by using body weight (BW), overestimates the amount of contrast material required in heavier patients.

Materials and Methods: Institutional review committee approval and patients' written informed consent were obtained. CT images of the abdomen were obtained by using 2 mL per kilogram of BW of intravenous contrast material (300 mg/mL iodine) injected at 4 mL/sec in 161 consecutive patients (age range, 28–90 years; mean age, 63 years; 95 men, 66 women). CT scans were initiated 45 and 150 seconds after aortic enhancement increased by 50 HU. The patients were divided into low (37–54 kg) and high (55–75 kg) BW groups. The HU/I, where HU is change in CT number and I is iodine dose in grams, and adjusted maximum hepatic enhancement (HU/[I/kg]) were assessed for correlation with BW, body mass index (BMI), and body fat percentage (BFP) by using linear regression.

Results: HU/I correlated (P < .001) inversely with BW in the aorta (r = –0.78) and liver (r = –0.80) and with BMI in the aorta (r = –0.59) and liver (r = –0.61) on portal venous phase images. Regression formula for the low BW group was HU/I = 4.1 – .044 · BW (P < .001) and for the high BW group was HU/I = 2.7 – .017 · BW (P < .001), suggesting that the amount of contrast material required with increased BW is less in the high BW group. Adjusted maximum hepatic enhancement directly correlated with BFP (r = 0.25, P < .01).

Conclusion: Excessive contrast material may inadvertently be given in heavier patients when the dose is determined by patient BW. Contrast material dose may need to be tailored in individual patients by using BFP.

© RSNA, 2008