Background

Perfusion magnetic resonance imaging (MRI) and delayed contrast-enhanced MRI (DE-MRI) serve as tools for tissue characterization.

Purpose

To assess and compare semi-quantitative parameters of myocardial infarct (MI) in the subacute and chronic phase, and to correlate these parameters with qualitative enhancement analysis.

Material and Methods

Perfusion MRI at rest and DE-MRI were performed in 63 patients with anterior wall MI at 2–3 weeks after revascularization and repeated after 6 months. Descriptive enhancement parameters of contrast arrival time, initial upslope, enhancement at normal tissue peak (TTP_n) and wash-out slope, and kinetic tissue parameters rBF, K ^trans, k _ep and v _e were calculated. Subacute infarct tissue was compared to normal myocardium and chronic infarct tissue. Patients were stratified at baseline according to a qualitative grading of hypoenhancement based on first-pass enhancement and presence of microvascular obstruction (MO) at perfusion MRI and on persistent MO at DE-MRI. The qualitative grade was correlated to semi-quantitative perfusion MRI parameters.

Results

Initial upslope, enhancement at TTPn, rBF, and k _ep were decreased and wash-out slope and v _e were increased in infarct tissue (P < 0.001 for all analyses). Infarct tissue v _e decreased from baseline to 6 months (P = 0.045). At baseline infarct tissue with persistent MO revealed decreased K ^trans and delayed contrast arrival, and more pronounced decrease of enhancement at TTPn, rBF and k _ep compared to other enhancement groups (P < 0.008 for pairwise analyses).

Conclusion

Perfusion is decreased in subacute reperfused infarct tissue compared to normal tissue. K ^trans is not decreased, consistent with increased surface area of the vascular bed of the subacute infarct. Infarct tissue v _e is increased, and decreases with scarring. The presence of persistent MO correlates to more pronounced perfusion reduction and results in delayed contrast arrival, indicating microvascular collateral circulation.