An Initial Clinical Evaluation of Quantitative Susceptibility Mapping for Quantitative Characterisation of Intramyocardial Hemorrhage

To characterise the performance of quantitative susceptibility mapping (QSM) for the detection of hemorrhagic iron in the context of ST elevation myocardial infarction (STEMI). Iron deposition following intramyocardial hemorrhage in STEMI has a mechanistic role in adverse left ventricular remodelling. Current MRI-based methods for measuring myocardial iron in STEMI, including T 2 *, T 1 , and T 2 mapping, are limited. Iron-mediated T 1 , T 2 , and T 2 * relaxation time shortening is opposed by edema-mediated prolongation of relaxation times, hindering the accuracy of these techniques. In contrast, QSM measures intrinsic tissue magnetic susceptibility, potentially resulting in higher specificity for iron detection in the setting of infarct-related myocardial edema. In this work, 22 patients with STEMI were scanned using QSM and T 2 * mapping sequences. Presence/absence of iron, image quality, and diagnostic confidence was assessed by two expert readers for QSM, T 2 * mapping, and T 2 * weighted imaging (longest echo-time T 2 * map source image). The volume of intramyocardial hemorrhage was quantified for each technique and compared to the volume of microvascular obstruction determined by late-gadolinium enhancement imaging. Mass of hemorrhagic iron in each case was determined using QSM and T 2 * maps. In the qualitative analysis, QSM had significantly improved diagnostic confidence and image quality compared to both T 2 * maps and T 2 * weighted images. For quantitative analysis the volume of intramyocardial hemorrhage determined by QSM had a significantly stronger correlation vs the reference standard than both T 2 * map and T 2 * weighted imaging. There was a strong correlation between the mass of hemorrhagic iron calculated by T 2 * map and QSM. This work demonstrates, in a patient population, the opportunity QSM presents for improving the assessment of hemorrhagic iron in the context of STEMI. Full evaluation in a large clinical trial is now warranted.