CT angiography of the renal arteries: comparison of lower-tube-voltage CTA with moderate-concentration iodinated contrast material and conventional CTA.

OBJECTIVE: The objective of our study was to investigate the feasibility of an 80-kVp protocol using a moderate-concentration contrast medium (CM) for CT angiography of the renal arteries by comparison with a conventional 120-kVp protocol using a high-concentration CM. SUBJECTS AND METHODS: Attenuation values and signal-to-noise ratios (SNRs) were determined in a phantom for the 120-kVp protocol with a high-concentration CM and the 80-kVp protocol with a moderate-concentration CM. In addition, 50 patients were prospectively enrolled in the study: 25 were scanned with 120 kVp and 200 effective mAs (mAs(eff)) after the administration of 110 mL of high-concentration CM (370 mg I/mL), and the other 25 were scanned with 80 kVp and 585 mAs(eff) after the administration of 110 mL of moderate-concentration CM (300 mg I/mL). Images of the two groups were compared in terms of arterial attenuation, SNR, contrast-to-noise ratio (CNR), and subjective degree of arterial enhancement and image quality.
RESULTS: The mean attenuation of the main renal artery was significantly higher (p < 0.001) in the 80-kVp group who received moderate-concentration CM (mean ± SD, 370.0 ± 65.0 HU) than in the 120-kVp group who received high-concentration CM (269.9 ± 27.8 HU) without significant differences in SNR and CNR values. The 80-kVp protocol had significantly higher quality scores for arterial enhancement, sharpness of the artery, and overall diagnostic quality compared with the 120-kVp protocol. The effective dose of the 80-kVp protocol (4.5 mSv) was 8.2% lower than that of the 120-kVp protocol (4.9 mSv).
CONCLUSION: The use of 80 kVp with moderate-concentration CM could improve arterial enhancement and provide superior image quality with a smaller amount of iodine and a lower radiation dose.

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