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

Purpose: To correlate signal behaviour in T-1- and T-2-weighted images afte r Gd-DTPA with regional histopathology in occlusive myocardial infarction ( MI). Methods: Ligation of a diagonal branch of the LAD was performed in sev en 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 imagi ng was performed at 1.5 T included T-1- and T-2-weighted spin echo sequence s in long and short axis views. Signal intensities (SI) were determined in 36 myocardial segments per slice and compared to macro- and microscopy. Res ults: In all animals an antero-lateral infarct region was evident histologi cally. This region presented with increased T2SI and T-1 SI after Gd-DTPA. The number of segments with increased SI in T-1-weighted images was higher (n=195 segments) compared to segments with increased T-2 SI (n=122 segments ). Granulation tissue could be differentiated from rarely vascularized conn ective tissue at a high level of significance (p<0.001) by T-1 and T-2 SI a nalysis. Walt thickness was significantly decreased in necrotic myocardium (3.8 +/- 1.2 mm) compared to normal tissue (9.8 +/- 1.1 mm, p < 0.001). Con clusion: In four-week-old occlusive MI the extent of necrosis can be accura tely assessed by analysis of post contrast T-1-weighted images. Considering regional T-2 SI, granulation tissue can be differentiated from regions wit h predominant fibrous organisation.