MR signal behaviour of four-week-old occlusive myocardial infarctions in sheep

Purpose: To correlate signal behaviour in T1- and T2-weighted images after Gd-DTPA with regional histopathology in occlusive myocardial infarction (MI). Methods: Ligation of a diagonal branch of the LAD was performed in seven sheep. Four weeks later 0.1 mmol Gd-DTPA/kg were injected in five sheep 15 min before cardiac arrest and the sheep were slaughtered. In vitro imaging was performed at 1.5 T included T1- and T2-weighted spin echo sequences in long and short axis views. Signal intensities (SI) were determined in 36 myocardial segments per slice and compared to macro- and microscopy. Results: In all animals an antero-lateral infarct region was evident histologically. This region presented with increased T2 SI and T1 SI after Gd-DTPA. The number of segments with increased SI in T1-weighted images was higher (n=195 segments) compared to segments with increased T2 SI (n=122 segments). Granulation tissue could be differentiated from rarely vascularized connective tissue at a high level of significance (p<0.001) by T1 and T2 SI analysis. Wall thickness was significantly decreased in necrotic myocardium (3.8±1.2 mm) compared to normal tissue (9.8±1.1 mm, p<0.001). Conclusion: In four-week-old occlusive MI the extent of necrosis can be accurately assessed by analysis of post contrast T1-weighted images. Considering regional T2 SI, granulation tissue can be differentiated from regions with predominant fibrous organisation. (orig.)