Direct detection of myocardial fibrosis by MRI

Excessive collagen deposition is a major hallmark of cardiac disease. Fibrosis reduces cardiac function and plays a major role in cardiac arrhythmogeneity. Despite the clinical importance, there is no non-invasive technique for direct detection of myocardial fibrosis yet. Ultra short echo time (UTE) MRI has been shown to detect tissues with a fast T₂* signal decay. Collagen has a fast T₂* signal decay compared to myocardium and should therefore be detectable with UTE MRI. This study aims to investigate the use of UTE MRI to detect fibrosis after myocardial infarction without using exogenous contrast. In 7 male Lewis rats either myocardial infarction was created (n = 5) or sham surgery was performed (n = 2). Six weeks after surgery, hearts were isolated and visualized by MRI. Images were acquired with UTE (TE 0.15 ms), to detect tissue with a fast T₂* decay. Acquired conventional images (TE = 6.0 ms) were subtracted from UTE images to maintain only ‘short living signal’ (SLS): tissue with a fast decay. In infarcted hearts, SLS was observed in subtracted images, whereas in control hearts hardly any SLS was detected. Subtracted images were cross-referenced with histology and showed that the SLS area observed with UTE MRI corresponded to the collagen-rich areas observed in histology. Normalized SLS areas correlated well with the normalized collagen-rich areas; r = 0.7, p = 0.002. We show for the first time that UTE MRI technology can be used for direct detection of post-infarcted fibrosis without the use of contrast agents.