Evaluation of Low-kVp Low-Volume Iodinated Contrast Protocol for Coronary CT Angiography Using Retrospective ECG Gating

Abstract

Objective The aim of this study was to evaluate the use of low peak kilovoltage (kVp) low-volume iodinated contrast protocol for performing coronary computed tomography (CT) angiography (CCTA) in patients using retrospective electrocardiogram (ECG) gating. Materials and Methods Hundred prospective patients undergoing CCTA were studied in two groups, A and B, using 70 kilovoltage (kV) and 120 kV protocols with half and standard intravenous volumes of injected iodinated contrast, respectively. All patients had heart rates less than 100 beats/min and body mass index (BMI) less than 31 kg/m ² . Both the groups were evaluated for signal-to-noise (S/N) and contrast-to-noise (C/N) ratios along with radiation dose delivered in millisievert (mSv), and for image quality (IQ), on per patient and per segment basis. Results Patients with group A showed statistically reduced radiation dose of 1.86 mSv compared with 6.86 mSv in group B patients. Marked reduction in image noise with statistically improved S/N and C/N ratios in all coronary vessels was seen in group A. S/N ratios in group A were 20.25, 18.68, 19.04, 17.41, and 18.69 for aorta, left main, left anterior descending, right coronary, and left circumflex arteries while they were 13.34, 11.12, 10.96, 9.74, and 8.67 in group B patients. C/N ratios were also higher in all vessels in group A patients, that is, 19.48, 19.48, 19.04, 19.48, and 17.68, compared with group B patients, who had 12.43, 10.03, 9.23, 9.57, and 8.23 ratios ( p < 0.0001). No significant difference in IQ per patient and per vessel was seen between both the groups. Discussion Retrospective ECG-gated low-kVp low-volume iodinated contrast protocol provides good diagnostic quality angiograms in patients with BMI up to 31 kg/m ² and with heart rates of less than 100 beats/min with three times reduced radiation dose. The reduced volume of contrast reduces the cost as well as the chance of contrast-induced nephropathy.

Keywords: coronary CT angiography; low kVp; radiation.

Fig. 1

Bar chart showing image noise in group A and group B patients.

Fig. 2

( A ) Group A patient with heart rate 65 beats/min axial section at the level of ascending aorta showing signal-to-noise ratio of 19.4 and 20.7 at proximal right coronary artery and proximal left anterior descending coronary artery, respectively. ( B ) Multiplanar view of left anterior descending coronary artery with image quality (IQ) of 4.0. ( C ) Multiplanar view of right coronary artery of same patient with IQ of 4 days. ( D ) Virtual rendering image of same patient.

Fig. 3

( A ) Group B patient showing axial section with signal-to-noise (S/N) ratio of 11.15 of left main and 23.0 of ascending aorta. ( B ) Axial section same patient with S/N of 9.7 of left circumflex artery. ( C ) Axial section of proximal right coronary artery with S/N of 10.0 days. Straightened multiplanar view of left anterior descending artery with image quality score of 4.0. ( E ) Virtual rendering image of heart of same patient.

Fig. 4

( A ) Group A patient with heart rate of 100 beats/min showing signal-to-noise ratio of 25 and 19.5 at proximal ascending aorta and left anterior descending coronary artery, respectively. ( B ) Virtual rendered image of same patient. ( C ) Multiplanar view of left anterior descending aorta with image quality of 4.

Fig. 5

( A ) Group A patient with heart rate of 81 beats/min showing signal-to-noise of 28 and 24.5 of proximal right coronary artery and ascending aorta, respectively. ( B ) Multiplanar view of same patient showing image quality of 3 with some vessel wall blurring.