Prospective versus Retrospective ECG-gated 64-Detector Coronary CT Angiography: Assessment of Image Quality, Stenosis, and Radiation Dose

Nobuhiko Hirai, MD Jun Horiguchi, MD Chikako Fujioka, RT Masao Kiguchi.RT Hideya Yamamoto, MD Noriaki Matsuura, MD Toshiro Kitagawa, MD HirokiTeragawa, MD Nobuoki Kohno, MD Katsuhide lto, MD

Purpose: To show that prospective electrocardiographically (ECG)-trig-gered coronary computed tomographic (CT) angiography (hereafter, prospective CT angiography) is at least as effective as retrospective ECG-gated coronary CT angiography (hereaf-ter, retrospective CT angiography).

Materials and Methods: Institutional review committee approval and informed con-sent were obtained. Sixty patients with heart rates of less than 75 beats per minute who were referred for coronary CT angiography were enrolled. Both prospective and retrospec-tive CT angiography were performed with a 64-detector scanner. Data acquisition times were recorded. Two inde-pendent cardiac radiologists evaluated subjective image qual-ity (1, excellent; 4, poor) and severity of stenosis (0% occlu-sion, l%-49% occlusion, 50%-75% occlusion, and >75% occlusion) with the 17-segment American Heart Association classification model. Discrepancies were settled by consen-sus. Effective radiation doses of prospective and retrospec-tive CT angiography were calculated with volume CT dose index. Data regarding acquisition time and radiation expo-sure for prospective and retrospective CT angiography were compared. The Student t test was performed, and K statistics were calculated.

Results: Mean data acquisition time of prospective CT angiography was shorter than that of retrospective CT angiography (5.6 sec-onds ±1.1 [standard deviation] vs 6.7 seconds ±1.1, respec-tively; P < .01). Consensus-determined image quality in coro-nary artery branches was similar between prospective CT an-giography and retrospective CT angiography (1.15 vs 1.13, respectively; P = .992). Excellent agreement between prospec-tive CT angiography and retrospective CT angiography was observed in the detection of significant (2:50% occlusion) coro-nary artery stenoses per segment (? = 0.882) and in the grading of stenoses per patient (? = 0.829). Calculated effective dose with prospective CT angiography was 79% lower than that with retrospective CT angiography (4.1 mSv ± 1.8 vs 20.0 mSv ± 3.5, respectively; P < .001).

Conclusion: Prospective CT angiography can reduce radiation dose be-low that of retrospective CT angiography with dose modula-tion, while maintaining image quality and the ability to assess luminal obstructions in patients with heart rates of less than 75 beats per minute.