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

Dong Wook Jeong, Ki Seok Choo, Seung Kug Baik, Yong Woo Kim, Ung Bae Jeon, Jeong Soo Kim, Soo Jin Lim
Acta Radiologica 2011 March 1, 52 (2): 155-60

BACKGROUND: 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.

PURPOSE: 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.

MATERIAL AND METHODS: 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.

RESULTS: 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.

CONCLUSION: 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.

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