320-row CT coronary angiography: effect of 100-kV tube voltages on image quality, contrast volume, and radiation dose

Abstract

To prospectively evaluate image quality parameters, contrast volume and radiation dose at the 100-kilovolt (kV) setting during coronary computed tomographic angiography (CCTA) on a 320-row computed tomography scanner. We enrolled 107 consecutive patients with a heart rate <65 beats per minute (bpm) undergoing prospective electrocardiogram (ECG)-triggered CCTA. Forty patients with a body mass index (BMI) <25kg/m(2) were scanned using 100-kV tube voltage settings, while 67 patients were scanned using 120-kV protocols. Image quality was assessed by two readers unaware of patient information and scan parameters. Attenuation in the aorta and perivascular fat tissue and image noise were measured. Contrast-to-noise ratios (CNRs) and contrast material volumes were calculated. The effective radiation doses were estimated using a chest conversion coefficient (0.017). Diagnostic image quality was achieved in 98.2% of coronary segments with 100-kV CCTA and 98.6% of coronary segments with 120-kV CCTA, with no significant differences in image quality scores for each coronary segment. Vessel attenuation, image noise, and CNR were not significantly different between the 100- and 120-kV protocols. Mean contrast injection rate and mean material volume were significantly lower for the 100-kV CCTA (4.35±0.28ml/s and 53.13±3.77ml, respectively) than for the 120-kV CCTA (5.16±0.21ml/s and 62.40±3.66ml respectively; P<0.001). The effective radiation dose was 2.12±0.19mSv for 100-kV CCTA, a reduction of 54% compared to 4.61±0.82mSv for 120-kV CCTA. A 100-kV CCTA can be implemented in patients with a BMI<25kg/m(2). The 100-kV setting allows significant reductions in contrast material volume and effective radiation dose while maintaining adequate diagnostic image quality.