4D Coronary MRA
Four-dimensional (4D) coronary MRA, recently proposed by researchers at Cedars-Sinai Medical Center to enable cardiac phase-resolved, high-resolution whole-heart coronary artery evaluation, is a promising technique to address the limitations of conventional protocols.
Coronary magnetic resonance angiography (MRA) is an emerging non-invasive method for coronary artery disease (CAD) detection. Compared with coronary computed tomography angiography (CTA), coronary MRA does not have ionizing radiation, and provides more accurate information at the presence of coronary calcification . Recent studies have shown that coronary MRA to have very good accuracy in detecting significant coronary stenosis compared with invasive x-ray angiography . Nevertheless, current coronary MRA techniques suffer from several limitations that prevent them from seeing wide clinical adoption, including 1) susceptibility to motion artifacts, 2) long and unpredictable imaging time, and 3) complex scan setup procedure. Four-dimensional (4D) coronary MRA, recently proposed by researchers at Cedars-Sinai Medical Center to enable cardiac phase-resolved, high-resolution whole-heart coronary artery evaluation, is a promising technique to address the limitations of conventional protocols.
The key feature of the 4D technique is that the cardiac and respiratory motion during the scan is handled retrospectively via self-gating, where the motion information is extracted from the raw MR data. Compared with the conventional prospective strategy for motion gating, the proposed method holds several advantages. Firstly, the fundamental assumption behind conventional prospective gating is the underlying motion being regular and periodic. As a result, image quality deteriorates when heart rate varies and respiratory pattern drifts. In contrast, the motion corrupted data is either corrected or discarded during the 4D reconstruction, thereby improving the method’s robustness to irregular motion patterns during the scan.
Secondly, when the subject’s breathing drifts significantly, the scan time of conventional coronary MRA protocols may become prohibitively long and the scan may even fail to finish. As a result, the scan time is unpredictable and can not be determined during scan planning. In 4D coronary MRA, the scanning efficiency is 100%, meaning the scan time is independent of the subject’s motion pattern, eliminating the scan time uncertainty.
Lastly, the conventional protocol relies on ECG and diaphragm navigator to extract motion information, which takes a significant amount of time and operator expertise to setup correctly. In contrast, 4D coronary MRA eliminates the need for external signal and instead uses self-gating for efficient retrospective motion gating, which allows for a greatly simplified, “push-button” scan workflow.
In conclusion, motion remains a significant challenge in cardiac MRI, especially for applications requiring high spatial resolution to resolve fine anatomical details such as coronary MRA. The proposed 4D coronary MRA technique addresses many limitations of the current suboptimal strategy, and represents a significant step towards robust, “push-button” cardiac MRI.
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 Liu, Xin, Xihai Zhao, Jie Huang, Christopher J. Francois, David Tuite, Xiaoming Bi, Debiao Li, and James C. Carr. "Comparison of 3D free-breathing coronary MR angiography and 64-MDCT angiography for detection of coronary stenosis in patients with high calcium scores." AJR. American journal of roentgenology189, no. 6 (2007): 1326.
 Pang, Jianing, Behzad Sharif, Zhaoyang Fan, Xiaoming Bi, Reza Arsanjani, Daniel S. Berman, and Debiao Li. "ECG and navigator‐free four‐dimensional whole‐heart coronary MRA for simultaneous visualization of cardiac anatomy and function." Magnetic Resonance in Medicine 72, no. 5 (2014): 1208-1217.
Jianing Pang received his BS in Physics from Peking University in 2009, and subsequently joined Dr. Debiao Li’s lab at Northwestern University in the same year to pursue a PhD in Biomedical Engineering with a focus on cardiovascular MRI, and graduated in 2014. He is currently a postdoctoral scientist at Cedars-Sinai Medical Center in Los Angeles, developing fast imaging and motion correction techniques for cardiovascular applications, such as coronary imaging.