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

doi:10.1148/radiol.2482071804

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Cardiac Imaging

Prospective versus Retrospective ECG-gated 64-Detector Coronary CT Angiography: Assessment of Image Quality, Stenosis, and Radiation Dose¹

Nobuhiko Hirai, MD, Jun Horiguchi, MD, Chikako Fujioka, RT, Masao Kiguchi, RT, Hideya Yamamoto, MD, Noriaki Matsuura, MD, Toshiro Kitagawa, MD, Hiroki Teragawa, MD, Nobuoki Kohno, MD, and Katsuhide Ito, MD

¹ From the Department of Clinical Radiology, Hiroshima University Hospital, 1-2-3 Kasumi-cho, Minami-ku, Hiroshima 734-8551, Japan (N.H., J.H., C.F., M.K.), and Department of Molecular and Internal Medicine, Division of Clinical Medical Science, Programs for Applied Biomedicine (H.Y., T.K., N.K.); Department of Radiology, Division of Medical Intelligence and Informatics, Programs for Applied Biomedicine (N.M., K.I.); and Department of Medicine and Molecular Science (H.T.), Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan. Received October 15, 2007; revision requested December 13; revision received January 14, 2008; accepted February 28; final version accepted March 5. Address correspondence to J.H. (e-mail: horiguch{at}hiroshima-u.ac.jp).

Purpose: To show that prospective electrocardiographically (ECG)-triggeredcoronary computed tomographic (CT) angiography (hereafter, prospectiveCT angiography) is at least as effective as retrospective ECG-gatedcoronary CT angiography (hereafter, retrospective CT angiography).

Materials and Methods: Institutional review committee approval andinformed consent were obtained. Sixty patients with heart rates ofless than 75 beats per minute who were referred for coronary CT angiographywere enrolled. Both prospective and retrospective CT angiographywere performed with a 64-detector scanner. Data acquisition timeswere recorded. Two independent cardiac radiologists evaluated subjectiveimage quality (1, excellent; 4, poor) and severity of stenosis (0%occlusion, 1%–49% occlusion, 50%–75% occlusion, and >75%occlusion) with the 17-segment American Heart Association classificationmodel. Discrepancies were settled by consensus. Effective radiationdoses of prospective and retrospective CT angiography were calculatedwith volume CT dose index. Data regarding acquisition time and radiationexposure for prospective and retrospective CT angiography were compared.The Student t test was performed, and ${kappa}$ statistics were calculated.

Results: Mean data acquisition time of prospective CT angiographywas shorter than that of retrospective CT angiography (5.6 seconds± 1.1 [standard deviation] vs 6.7 seconds ± 1.1, respectively;P < .01). Consensus-determined image quality in coronary arterybranches was similar between prospective CT angiography and retrospectiveCT angiography (1.15 vs 1.13, respectively; P = .992). Excellentagreement between prospective CT angiography and retrospective CTangiography was observed in the detection of significant ( $≥$ 50% occlusion)coronary artery stenoses per segment ( ${kappa}$ = 0.882) and in the gradingof stenoses per patient ( ${kappa}$ = 0.829). Calculated effective dose withprospective CT angiography was 79% lower than that with retrospectiveCT angiography (4.1 mSv ± 1.8 vs 20.0 mSv ± 3.5, respectively;P < .001).

Conclusion: Prospective CT angiography can reduce radiation dosebelow that of retrospective CT angiography with dose modulation,while maintaining image quality and the ability to assess luminalobstructions in patients with heart rates of less than 75 beats perminute.

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