Coronary CT angiography with single-source and dual-source CT: Comparison of image quality and radiation dose between prospective ECG-triggered and retrospective ECG-gated protocols
Introduction
Coronary CT angiography (CCTA) has gained a leading role in the diagnosis of coronary artery disease (CAD) due to its high diagnostic value, in particular, a very high negative predictive value (95–99%) [1], [2]. With 64- or more slice CT, non-invasive CCTA has become a reliable alternative to invasive coronary angiography in the diagnosis of patients with suspected CAD [2].
Traditionally, CCTA was performed using retrospective ECG gating, which enables acquisition of volume data, but at the expense of high radiation dose, since data is acquired during a spiral CT protocol [3]. High radiation dose associated with retrospective ECG-gated CCTA raised major concerns in the literature; thus, strategies for reducing radiation dose in retrospective ECG gating have been developed and widely introduced in present-day clinical centers. These strategies include tube current modulation that is either attenuation-based [4], [5] or ECG-control-based [6], [7], lower tube voltage [8], [9], high-pitch scanning [10], [11], and prospective ECG triggering [3], [12], [13]. Of these strategies, prospective ECG triggering represents the most effective approach with a significant dose reduction when compared to the conventional retrospective ECG-gated protocol, but with high diagnostic image quality.
Unlike the principle of retrospective ECG gating, the principle of prospective ECG triggering is that data acquisition takes place only in the selected cardiac phase by selectively turning on the X-ray tube when triggered by the ECG signal, and turning it off or dramatically lowering it during the rest of the R–R cycle [3].
Radiation dose and image quality with prospective ECG triggering are increasingly being studied and compared with retrospective ECG gating in the literature [14], [15], [16], [17]. Despite the promising results that have been achieved in dose reduction and image quality, there is a concern about the accuracy of effective dose calculation. Moreover, to our knowledge there is a lack of systematic investigation on image quality comparison between different types of scanners (single-source vs. dual-source CT) with prospective and retrospective ECG-gated CCTA techniques. Therefore, the aim of this study was to investigate and compare image quality and radiation dose between prospective ECG-triggered and retrospective ECG-gated CCTA protocols, using different types of 64-slice CT scanners.
Section snippets
Study population
This is a cross-sectional study comparing radiation dose and image quality between prospective triggered and retrospective ECG-gated CCTA in two major public hospitals, Royal Perth Hospital, Perth, Australia, and National Heart Institute, Kuala Lumpur, Malaysia. The study was approved by both institutional ethical review boards. The first part of the study was conducted retrospectively between January and July 2011 in the Royal Perth Hospital with 95 patients with suspected CAD who underwent
Results
Details on patient demographics, CAD risk factor and beta-blocker usage are presented in Table 2. A total of 2880 coronary artery segments were evaluated. However, 793 segments (mainly posterior lateral branch, second diagonal artery, second obtuse marginal branch and ramus intermedius segment) were not considered because of anatomical variants. Therefore, 2087 segments were assessable of which 2046 (98.0%) segments were ranked as of sufficient image quality (score 1 to 3), while only 41
Discussion
This study demonstrates two main findings which are useful for clinical study. Firstly, there was no significant difference in image quality between prospective ECG-triggered and retrospective ECG-gated CCTA regardless of the use of SSCT or DSCT scanner. All images were presented with sufficient quality in more than 96% of the coronary segments. Secondly, prospective ECG-triggered CCTA leads to a significant lower radiation dose compared to with a retrospective ECG-gated technique performed
Acknowledgments
The authors of this manuscript have certified that they have complied with the Principles of Ethical Publishing in the International Journal of Cardiology.
The authors would like to thank Mohd Zaidi Abdul Rahman and Rizal Saim from the National Heart Institute and Melanie Rosenberg from the Royal Perth Hospital for their assistance in CT data collection.
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