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DOI:10.2214/AJR.05.0052
AJR 2006; 187:W1-W6
© American Roentgen Ray Society

Original Research

Variability of Repeated Coronary Artery Calcium Measurements on Low-Dose ECG-Gated 16-MDCT

Jun Horiguchi1, Hideya Yamamoto2, Nobuhiko Hirai1, Yuji Akiyama1, Chikako Fujioka1, Kazushi Marukawa3, Hiroshi Fukuda1 and Katsuhide Ito3

1 Department of Clinical Radiology, Hiroshima University Hospital, 1-2-3, Kasumi-cho, Minami-ku, Hiroshima 734-8551, Japan.
2 Department of Molecular and Internal Medicine, Division of Clinical Medical Science, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
3 Department of Radiology, Division of Medical Intelligence and Informatics, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.

OBJECTIVE. High reproducibility on coronary artery calcium (CAC) scoring is a key requirement in monitoring the progression of coronary atherosclerosis. Retrospective ECG-gated helical CT has been shown to be superior to prospective gating helical CT in the reproducibility of CAC measurements. However, it brings with it a high level of radiation exposure. The purpose of this study was to compare low- and standard-dose protocols in the variability of CAC scores and in image quality, thereby assessing the feasibility of low-dose retrospective ECG-gated helical CT in CAC measurements.

SUBJECTS AND METHODS. Eighty-six patients with CAC were scanned using a tube current setting of 100 mA once and then a tube current setting equivalent to the patient's body weight twice. CAC scores (Agatston and volume) and interscan variability were evaluated. The mean and SD of the CT attenuation values in regions of interest in the aorta were measured, and the value (mean + 2 x SD) was obtained.

RESULTS. A high correlation of log10 (Agatston score + 1) was observed between sequential helical CT scans (r = 0.998). The variability in CAC measurements ranged from 11% to 12% for both the Agatston and volume scores. With the tube current equivalent to body weight, the value (mean + 2 x SD) did not exceed a CT attenuation value of 130 H.

CONCLUSION. Low-dose retrospective ECG-gated helical CT—yielding low variability and achieving the level of image quality needed to measure CAC—can be used to monitor patients with coronary atherosclerosis.

Keywords: atherosclerosis • cardiac imaging • coronary artery disease • MDCT


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