Image Quality in a Low Radiation Exposure Protocol for Retrospectively ECG-Gated Coronary CT Angiography

OBJECTIVE. The purpose of our study was to systematically compare the image quality of dual-source CT coronary angiography using 100 kV instead of 120 kV. SUBJECTS AND METHODS. One hundred patients with a body weight = 85 kg were included. A dual-source CT scanner was used (330-milliseconds rotation, 0.6-mm collimation, 56 +/- 7 mL of IV contrast agent at 5 mL/s). Each patient was randomized either to scanning protocol group 1 (120 kV and 330 mAs) or protocol group 2 (100 kV and 330 mAs). ECG pulsing was used for all patients. Data sets were assessed by two independent observers for image quality, signal-to-noise ratio, and contrast-to-noise-ratio. Effective dose was determined based on dose-length product. RESULTS. There were no significant differences in body weight or heart rate between the two groups (70 +/- 10 kg and 57 +/- 8 bpm [beats per minute] vs 70 +/- 9 kg and 59 +/- 8 bpm). Use of 100 kV led to significant reduction of radiation exposure (group 1: 12.7 +/- 1.7 mSv; volume CT dose index [CTDI(vol)], 47.8 +/- 6.1 mGy and group 2: 7.8 +/- 2.0 mSv; CTDI(vol), 28.6 +/- 6.3 mGy; p < 0.001). Interobserver agreement in assessing image quality (kappa = 0.71) was close. Mean patient-based image quality scores were not significantly different (group 1, 2.7 +/- 0.5 and group 2, 2.6 +/- 0.4; p = 0.75). Also, vessel-based scores showed no significant differences. Beyond the level of significance, group 1 and group 2 showed one and two nonassessable patients and two and three nonassessable vessels, respectively. Mean intraluminal attenuation, contrast enhancement, and image noise were significantly higher for 100 kV, whereas signal-to-noise and contrast-to-noise-ratios were not different between the two scanning protocols. CONCLUSION. The use of lower tube voltage leads to significant reduction in radiation exposure in noninvasive coronary CT angiography. Image quality in nonobese patients is not negatively influenced.