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Radiation Dose, Image Quality, Stenosis Measurement, and CT Densitometry Using ECG-Triggered Coronary 64-MDCT Angiography: A Phantom Study

¹ Department of Clinical Radiology, Hiroshima University Hospital, 1-2-3, Kasumi-cho, Minami-ku, Hiroshima, 734-8551, Japan.
² CT Lab of Great China, GE Healthcare, Mongkok, Kowloon, Hong Kong.
³ GE Yokogawa Medical Systems, Tokyo, Japan.
⁴ Department of Radiology, Division of Medical Intelligence and Informatics, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.

OBJECTIVE. The purpose of this study was to compare prospective ECG-triggered and retrospective ECG-gated coronary 64-MDCT angiography as to radiation dose, image quality, accuracy of stenosis measurement, and CT densitometry.

MATERIALS AND METHODS. Coronary artery models (n = 3) with different plaque densities ( 50, 110, and 1,000 H) on a cardiac phantom were scanned in variable heart rate sequences (n = 14) with both prospective ECG-triggered and retrospective ECG-gated scanning. Radiation dose, image quality graded by motion and stairstep artifacts (grade 1, excellent, to grade 4, poor, with grades 1 and 2 defined as satisfactory), accuracy of stenosis measurement (area; 18%, 50%, and 82%), and CT densitometry of plaques (soft, 50; and intermediate, 110 H) were compared between the two protocols using the Mann-Whitney U test and repeated measures.

RESULTS. The radiation dose of prospective ECG-triggered CT angiography (CTA) (3.0 mSv) was lower than that of retrospective ECG-gated CTA (11.7–13.0 mSv) when the same tube current (mA) and voltage (kVp) were used in both methods. Prospective ECG-triggered CTA images were assigned a satisfactory quality rating in stable heart rate up to 75 beats per minute (bpm) when using the minimal X-ray exposure time. In this range, there were no significant differences in stenosis measurement (p = 0.17) and CT densitometry (p = 0.93) between the two protocols.

CONCLUSION. Prospective ECG-triggered coronary 64-MDCT has the potential to reduce radiation exposure while maintaining the diagnostic performance of retrospective ECG-gated coronary 64-MDCT.

Keywords: cardiac imaging • coronary artery • CT angiography • densitometry • radiation dose • stenosis measurement

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