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16-MDCT Angiography in Living Kidney Donors at Various Tube Potentials: Impact on Image Quality and Radiation Dose

¹ All authors: Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114-2696.

OBJECTIVE. The objective of our study was to compare the performance of 16-MDCT angiography at various peak kilovoltage (kVp) settings and the impact of the different settings on image quality and on radiation dose in adult kidney donors.

MATERIALS AND METHODS. Sixty-two renal donors (32 men, 30 women) who underwent 16-MDCT were divided into three groups: 18 subjects were studied at 140 kVp (group A); 20, at 120 kVp (group B); and 24, at 100 kVp (group C). Other constant scanning parameters were as follows: detector collimation, 0.625 mm; table feed, 9.375 mm/rotation; gantry rotation time, 500 milliseconds; and automatic current tube modulation (ATCM) using a noise index of 15. A total of 135-140 mL of iodinated contrast material (300 mg I/mL) was administered at 5 mL/s via an 18-gauge cannula, and arterial phase scanning was initiated using a bolus-tracking technique. Two observers evaluated image quality of the axial and 3D images and the visibility of branch order in the superior mesenteric artery (SMA) and renal arteries. Attenuation (in Hounsfield units [H]) in the aorta, SMA, and main renal artery was also measured by placing a region of interest. Radiation dose measurements were based on the scanner-generated CT dose index volume (CTDI_vol). Each parameter tested was compared among the three groups using a nonparametric analysis of variance test, and a p value of 0.05 was considered significant.

RESULTS. Differences in the quality of the axial images existed between groups A and C (p < 0.001) and between groups B and C (p < 0.01); the image quality of the 3D images and the visibility of branch order in the SMA and renal arteries were comparable for all groups. The difference in mean attenuation of the aorta, SMA, and renal arteries was significant between groups A and C (p < 0.001) and between groups B and C (p < 0.01). All groups had 100% diagnostic accuracy in identifying the number of renal arteries on the side of nephrectomy. The mean radiation dose in CTDI_vol was 25 ± 3 mGy at 140 kVp, 17 ± 4 mGy at 120 kVp, and 12 ± 3 mGy at 100 kVp (p < 0.001).

CONCLUSION. Our initial observations suggest that the image quality of 16-MDCT angiography performed at 120 kVp is similar to that of CT angiography (CTA) performed at 140 kVp in adult kidney donors but with a significant radiation dose reduction. CTA at 100 kVp results in higher image noise but provides diagnostically acceptable images with significant radiation dose reduction compared with CTA at 120 or 140 kVp.

Keywords: kidney transplantation • MDCT angiography • oncologic imaging • radiation dose • renal artery

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