Conventional high resolution versus fast T2-weighted MR imaging of the heart: assessment of reperfusion induced myocardial injury in an animal model

Cardiac image quality in terms of spatial resolution and signal contrast was assessed for conventional and newly developed T2-weighted fast spin-echo imaging with high k-space segmentation. The capability in revealing regional myocardial edema and cellular damage was examined by a porcine model using histopathologic correlation. Twelve porcine hearts were excised from slaughtered animals and instantly perfused with 1000 mL cold cardioplegic solution. After 4 h of cold ischemia the hearts were reperfused for one hour using a “Langendorff” perfusion model followed by MR imaging at 1.5 Tesla. Three additional pig hearts served as controls and were studied by MR directly after harvesting. Histopathological analysis of regional tissue changes was performed macro- and microscopically. Short axis T2-weighted (3000/45 and 90) high quality fast spin-echo (FSE) images were recorded without cardiac action and signal intensity was correlated with histology. These images also served as gold standard for evaluation of newly developed faster sequences allowing measuring times shorter than 20 s. Fast T2-weighted imaging comprised single-slice fast spin echo (moderate echo train length of 23 echoes, FSEm), and multi-slice single-shot half-Fourier fast spin-echo (71 echoes, FSEHASTE) sequences, supplemented by versions with inversion recovery preparation (FSEmIR and FSEHASTEIR). Systolic function after reperfusion was restored in 10 porcine hearts. Tissue alterations included myocardial edema and contraction band necrosis which was found to be most severe in myocardium with maximum T2 SI. Especially FSEm and FSEmIR sequences allowed differentiation of all categories of tissue damage on a high level of significance. In contrast, single-shot FSEHASTE and FSEHASTEIR sequences did not provide sufficient image quality to discriminate moderate and severe myocardial damage (p > 0.05). Different degrees of myocardial injury after ischemia and reperfusion can be staged by MR imaging, especially using conventional high resolution T2-weighted FSE sequences. The animal study indicates that fast T2-weighted FSEm and FSEmIR sequences lead to superior image quality and diagnostic accuracy compared to FSEHASTE and FSEHASTEIR imaging.