Step-and-shoot prospectively ECG-gated versus retrospectively ECG-gated with tube current modulation coronary CT angiography using the 128-slice MDCT: comparison of image quality and radiation dose

Abstract

Little is known regarding image quality and the required radiation dose for step-and-shoot and retrospective coronary computed tomography angiography (CCTA) with tube current modulation (TCM) in 128-slice multidetector CT (MDCT) coronary angiography. To compare image quality and radiation dose in patients who underwent 128-slice MDCT by the step-and-shoot method with those in patients who underwent 128-slice MDCT with retrospective CCTA with TCM. CCTA obtained with 128-slice MDCT was retrospectively evaluated in 160 patients. Two independent reviewers separately scored the subjective image quality of the coronary artery segments (1, excellent; 4, poor) for step-and-shoot (68, mean heart rate [HR]: 59.3 ± 6.8) and retrospective CCTA with TCM (77, mean HR: 59.1 ± 9.8). Interobserver variability was calculated. Effective radiation doses of both scan techniques were calculated with dose-length product. There was good agreement for quality scores of coronary artery segment images between the independent reviewers (κ = 0.72). The number of coronary artery segments that could not be evaluated was 2.85% (27 of 947) in the step-and-shoot and 1.87% (20 of 1071) in retrospective CCTA with TCM. Image quality scores were not significantly different (P > .05). Mean patient radiation dose was 63% lower for step-and-shoot (1.94 ± 0.70 mSv) than for retrospective CCTA with TCM (4.51 ± 1.18 mSv) (P < 0.0001). For patients who underwent step-and-shoot or retrospective CCTA with TCM, an average HR of 63.5 beats per minute was identified as the threshold for the prediction of non-diagnostic image quality for both protocols. There were no significant differences in the image quality of both methods between obese (body mass index [BMI] ≥ 25) and non-obese patients (BMI < 25), but radiation doses were higher in the obesity group than in the non-obesity group for both methods. Both step-and-shoot and retrospective CCTA with TCM using 128-slice MDCT had similar subjective image quality scores, but step-and-shoot required a lower radiation dose than retrospective CCTA with TCM.