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Contrast Enhancement in Cardiovascular MDCT: Effect of Body Weight, Height, Body Surface Area, Body Mass Index, and Obesity

¹ Department of Radiology, University of Pittsburgh School of Medicine, 200 Lothrop St., Ste. 4895, Pittsburgh, PA 15213.
² Division of Cardiology, Washington University School of Medicine, St. Louis, MO.
³ Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO.
⁴ Department of Radiology, Gifu University School of Medicine, Gifu, Japan.

OBJECTIVE. The purpose of our study was to evaluate the effect of body weight, height, body surface area (BSA), body mass index (BMI), and obesity on aortic contrast enhancement in cardiac MDCT.

MATERIALS AND METHODS. Seventy-three consecutive patients underwent cardiac CT angiography on a 64-MDCT scanner. Seventy-five mL of contrast medium (350 mg I/mL) was injected at 4.5 mL/s, followed by a 40-mL saline flush at 4.5 mL/s. The scanning delay of CT was determined with a bolus tracking technique. Aortic attenuation was measured over the aortic-root lumen. BMI and BSA were calculated from the patient's body weight and height. The patients were divided into low-(BMI < 30) and high-( 30) BMI groups. Associations of aortic attenuation with body weight, height, BMI, and BSA were evaluated with regression analysis and the Student's t test.

RESULTS. Strong inverse correlations were seen between aortic attenuation and body weight (r = –0.73), height (r = –0.47), BMI (r = –0.63), and BSA (r = –0.74) (p < 0.001 for all). The regression formula of aortic attenuation versus body weight suggests that 1.0 mL/kg of contrast medium would yield a mean aortic attenuation of 355 H. The mean aortic attenuation was significantly higher in the low-BMI (352.6 ± 59.1 H) than in the high-BMI (286.2 ± 55.5 H) group. The regression formula for aortic attenuation on body weight was aortic attenuation = 586–3.1 body weight (p < 0.001) for the low-BMI group and aortic attenuation = 485–1.9 body weight (p < 0.001) for the high-BMI group, suggesting that the amount of contrast medium required with increased body weight is less in the high-BMI group. This group difference was less pronounced for the regression of aortic attenuation on BSA.

CONCLUSION. To achieve a consistent contrast enhancement in cardiac CT angiography (CTA), contrast-medium dose should be adjusted with the body weight or the BSA (which accounts for both the body weight and height factors) to provide adjustment of iodine dose over a wide range of body sizes.

Keywords: aorta • cardiac CT • CT angiography • vascular imaging

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