How can we correlate cardiac MRI to histological findings? Right after STEMI, T2-weighted imaging and T2* mapping cardiac MRI depicts edema and IMH, respectively. Late gadolinium enhancement (LGE) cardiac MRI is used to measure the acute infarct size. As T2 values change dynamically over the first few days after STEMI and the severity of T2 abnormalities can be modulated with treatment, T2-weighted MRI should not be used for depicting area-at-risk. LGE cardiac MRI is the most accurate method to visualize MVO which identifies microvascular injury, hemorrhage, and necrosis in histologic samples. To detect replacement fibrosis (i.e., final infarct size after injury healing), LGE cardiac MRI is used in the chronic setting post-STEMI.
Though native T1 mapping is inferior to LGE cardiac MRI, it has recently emerged as a contrast material-free method to measure infarct size. With LGE cardiac MRI-defined infarct size combined with MVO can be used to monitor the effect of new therapeutic interventions in the treatment of reperfusion injury and infarct size reduction.