Introduction

Coronary magnetic resonance angiography (MRA) is a safe, non-invasive, radiation and iodinated contrast-free potential alternative for imaging coronary artery stenosis. Still, it has yet to be widely used in clinical practice (1) due to lower diagnostic accuracy than coronary computed tomography angiography (CTA) (2,3). There are two relatively quiescent periods in the cardiac cycle, mid-diastole, and end-systole, for acquiring coronary images (4). The clinical applications of coronary MRA combining diastole and systole imaging have never been described comprehensively in coronary artery disease (CAD) patients. We aimed to design an optimal non-contrast coronary MRA scan protocol combining diastole and systole imaging and to evaluate its diagnostic performance for detecting significant CAD.

Methods

In this prospective study, 91 patients scheduled for CAG were enrolled for coronary MRA. 3.0-T (Ingenia CX, Netherland, Best) non-contrast whole-heart coronary MRA was carried out twice at diastole and systole. Two radiologists who were blinded to the CAG results assessed the images independently. The image quality of each coronary artery segment was rated on the following four-point scale: 1 = poor, non-assessable with severe image artifacts; 2 = fair, assessable with moderate image artifacts; 3 = good, assessable with minor artifacts; and 4 = excellent, assessable with no apparent artifacts. Scores of the two observers were averaged for image quality analysis. Significant coronary stenosis was defined as a luminal diameter reduction of ≥ 50% using CAG as the reference and was evaluated as follows:1) by coronary MRA at diastole alone; 2) by coronary MRA at systole alone 3) by combined coronary MRA (diastole and systole images). For combined coronary MRA analysis, only location-matched stenosis presented in both modes was determined to be significant. Otherwise, it was defined as having no significant stenosis. Consensus reading was performed for the segments with disagreement between the two observers.

Results

The study participants' inclusion flowchart is shown in Figure 1. The diastolic and systolic coronary MRA was completed in 76 patients. The total time of two coronary MRA scanning was 16.2 ± 3.1 min, and acquisition time was longer at systole than at diastole (8.9 ± 2.1 min vs. 7.3 ± 1.6 min, P < 0.001). The comparison of image quality between diastolic and systolic coronary MRA is shown in Figure 2 - Table 1. The overall image quality at systole was higher than at diastole (P < 0.001), particularly in middle-distal segments.The diagnostic performance of coronary MRA for detecting significant coronary stenoses using the three strategies is listed in Figure 3 -Table 2. For the three coronary MRA strategies (diastolic, systolic, and combined), there was no significant difference in sensitivity on a per-patient, per-vessel, and per-segment basis (P > 0.05 for all). At the same time, the specificity and accuracy were significantly different on a per-patient, per-vessel, and per-segment basis (P < 0.05 for all). Compared with diastolic coronary MRA, systolic coronary MRA had similar specificity and accuracy on a per-patient, per-vessel, and per-segment basis (adjusted P > 0.05 for all). Compared with diastolic coronary MRA, combined coronary MRA had significantly higher specificity and accuracy on a per-patient, per-vessel, and per-segment basis (adjusted P < 0.05 for all). Figure 4 illustrates the diagnostic performance of coronary MRA combining diastole and systole.

Discussion

This study found that systole imaging offered better image quality in middle-distal segments. However, the mean imaging time of coronary MRA was longer at systole than diastole. We showed higher sensitivity but relatively lower specificity by the diastole or systole mode alone, with no significant difference between diastole and systole. Compared with diastole, the duration of systole is less affected by HR variability (5). End-systolic imaging may be an alternative to more conventional diastolic imaging to minimize the adverse effects of RR variability. However, the abbreviated systolic rest period necessitates image data collection in a relatively short acquisition window, which prolongs scanning time. The long acquisition time increases the chance of respiratory pattern and drift bulk motion and degrades the final image quality. Therefore, both methods have advantages and disadvantages and could be helpful for clinical applications of coronary MRA. In our study, when diastole and systole images were combined, more false positive interpretations for poor image quality and ambiguous local artifacts were corrected, enhancing diagnostic specificity.

Conclusion

3.0-T non-contrast coronary MRA at diastole or systole can noninvasively detect coronary stenoses with high sensitivity and moderate specificity. Combined coronary MRA at 3.0-T significantly improved diagnostic performance, especially specificity, compared with single-phase coronary MRA mode.

Acknowledgements

The authors thank the members of the Center of Cardiac Magnetic Resonance team at the Zhongshan Hospital Affiliated to Fudan University and the MR technologists for their valuable participation, helpfulness, and support during this study.

References

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