Individually adapted coronary 64-slice CT angiography based on precontrast attenuation values, using different kVp and tube current settings: evaluation of image quality

To evaluate the feasibility of an individually adapted coronary CT protocol based on precontrast attenuation values using different kVp and tube current settings. All images were acquired on a 64-slice CT scanner (Sensation 64, Siemens) in 270 consecutive patients. X-ray tube current and kVp settings were defined in 6 groups depending on the noise measurements at the heart level on pre-control unenhanced CT. The contrast medium was 400 mg/ml of iodine given at 1 ml/kg. The duration of injection was at 17 s in all cases, so the flow rate was adapted accordingly. Contrast enhancement and noise were measured from enhanced scans of the aortic root. The contrast to noise ratio (CNR) was used as an indicator of image quality. The mean contrast enhancement was 391 ± 83 HU. The mean radiation dose was 9.4 mSv (1.4–30.4 mSv). The mean noise was 39.8 ± 7.7 HU; noise was not significantly different between the groups, except for the 80 kVp group (mean noise = 54.5 HU, P < 0.05). The mean CNR was 10.1 ± 2.5, and CNR was similar in groups 1, 3, 4, and 5 (scanned at 80 kVp or 120 kVp), but significantly higher (CNR = 12) in group 2 (100 kVp) and significantly lower (CNR = 7.9) in group 6 (140 kVp). Individual adaptation of radiation dose is feasible in routine clinical coronary multislice CT, at various kVp and mAs settings. Image quality may be preserved with substantial radiation dose savings in patients with low attenuation values on precontrast images.