Simultaneous bright‐ and black‐blood whole‐heart MRI for noncontrast enhanced coronary lumen and thrombus visualization

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Coronary artery disease (CAD) primarily is caused by the formation and progressive growth of atherosclerotic plaque, which can lead to the narrowing of one or several of the coronary arteries and subsequent angina 1. Catheter‐based X‐ray coronary angiography remains the gold standard for the detection of CAD. However, a major challenge of CAD diagnosis remains that 50% of patients experiencing myocardial infarction have angiographically normal coronary arteries and no previous symptoms. In fact, plaque growth may occur with preserved coronary lumen size, also called “outward or positive arterial remodeling” 2, thus evading detection by luminographic imaging techniques. As the plaque increases, in size its tissue composition changes and may lead to plaque destabilization and eventually rupture, causing myocardial infarction or stroke due to occlusive thrombosis. The persistent presence of nonocclusive mural or intraluminal thrombosis also can cause sudden blockage and life‐threatening events through, for example, embolization. Recent studies have shown that coronary plaque burden, intraplaque hemorrhage, and thrombus carry significant prognostic value for the prediction of future coronary events 3. Thus, early detection of these features may allow to better risk stratify patients and ultimately improve patient outcome. Therefore, the ideal diagnostic test for CAD should simultaneously and noninvasively provide location/degree of lumen stenosis and detection/characterization of coronary plaque and thrombus.
MRI has shown great potential for noninvasive coronary lumen 4, thrombus/hemorrhage 5, and plaque visualization 3 in CAD patients. However, MR coronary lumen, thrombus/hemorrhage, and plaque assessment often suffers from image quality degradation due to physiological motion (during and between acquisitions) and prolonged scan times.
Coronary lumen visualization is achieved with bright‐blood coronary MR angiography (CMRA). 3D whole‐heart CMRA typically is performed with 1D diaphragmatic navigator gating and tracking to compensate for the respiratory motion of the heart 8. This approach leads to prolonged and unpredictable scan times because only a fraction of the acquired data (referred to as scan efficiency) is accepted for image reconstruction. Several advanced motion correction techniques have been proposed for CMRA during the last decade that allow the extraction of respiratory motion information directly from the imaging data, thus enabling 100% scan efficiency and more predictable scan times 9.
Characterization of coronary intraplaque hemorrhage and thrombus has been demonstrated using a 3D black‐blood noncontrast enhanced T1‐weighted inversion recovery (IR) sequence 5. Such approach exploits the short T1 of methemoglobin that is present in acute thrombus and intraplaque hemorrhage. Because the signal from the background tissues appears strongly suppressed in T1‐weighted black‐blood images, an additional bright‐blood CMRA needs to be acquired as anatomical reference; typically, the coronary lumen bright‐blood and the coronary thrombus/hemorrhage black‐blood acquisitions are performed sequentially. Similar sequential approaches have been successfully applied for coronary plaque characterization in patients with CAD 3.
Because the black‐blood and bright‐blood acquisitions usually are performed under free‐breathing, 1D diaphragmatic navigator gating and tracking 8 is used to account for respiratory motion. Aside from leading to prolonged and unpredictable scan times, as previously described for conventional CMRA, this sequential approach can lead to misregistration artifacts between the bright‐blood and black‐blood datasets. A 3D whole‐heart and respiratory self‐navigated radial sequence (CATCH) recently has been introduced, and it addresses some of these drawbacks by acquiring a black‐blood IR sequence and an anatomical bright‐blood reference in an alternate fashion 21. With this approach, however, the reconstruction scheme relies on respiratory motion parameters that are partially shared among the bright‐blood and the black‐blood data; as such, the risk of misregistration errors may be not entirely avoided.

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