Depiction of reperfused myocardial infarction using contrast-enhanced spin echo and gradient echo magnetic resonance imaging

RATIONALE and OBJECTIVES. The authors used gadolinium (Gd) chelate as a T1, T2, and T2* enhancing agent in reperfused myocardial infarction to compare the appearance of reperfused myocardial infarction on spin echo and gradient echo magnetic resonance (MR) sequences. METHODS. Rats (n = 28) were subjected to reperfused myocardial infarction and received no contrast medium, 0.2, 0.5, or 1.0 mmol/kg Gd DTPA-BMA. Spin echo and gradient echo MR images of the excised hearts (n = 7 rats per group) were acquired using 2.0 T system: repetition time (TR)/echo time (TE) = 300/20 ms for T1-weighted spin echo, TR/TE = 4000/80 ms for T2-weighted spin echo, and TR/TE = 600/10, 15, 20, and 30 ms for gradient echo imaging. Regional T2 and T2* relaxation times were measured. Triphenyl tetrazolium chloride was used to verify regional infarction. RESULTS. Unenhanced spin echo images failed to distinguish infarcted from normal myocardium. On Gd DTPA-BMA enhanced T1- weighted spin echo images, infarction was depicted as a high-intensity region 'hot spot.' On the other hand, the infarcted region was visualized as a low- signal region 'cold spot' on Gd DTPA-BMA enhanced T2-weighted images. Changes in signal intensity and T2 relaxation time on T2 weighted images were dose dependent. On gradient recalled echo images, the infarcted region was discriminated from normal myocardium by a dark boundary zone, which was visible only at 1.0 mmol/kg. The presence of infarction was documented in every heart. CONCLUSIONS. The contrast between normal and infarcted myocardium was affected greatly by the dose and imaging parameters. The results indicate that spin echo and gradient echo images have greatly differing sensitivities to extracellular gadolinium chelates. Changes in myocardial T2 relaxation time, but not T2*, correlated well with the dose.