PARAMAGNETIC METALLOPORPHYRINS - INFARCT AVID CONTRAST AGENTS FOR DIAGNOSIS OF ACUTE MYOCARDIAL-INFARCTION BY MRI

In previous experiments in tumors we demonstrated that metalloporphyri ns are particularly avid for nonviable tumor components. This study wa s performed to find out whether these agents can be used as MRI contra st agents for the visualization of acute myocardial infarction (MI). A total of 44 rats, 6 normal controls and 38 with occlusive MI (2-24 h old), were used. Gadolinium mesoporphyrin (Gd-MP) or manganese tetraph enylporphyrin (Mn-TPP) was intravenously injected at doses of 0.1, 0.0 5, 0.01 mmol/kg. Three to 24 h after injection, axial and coronal T1-w eighted (TR/TE 300/15 ms) spin-echo MR images were obtained before and after killing the animals and correlated with triphenyl tetrazolium c hloride (TTC) histochemical preparations. The Gd-MP content in infarct ed and noninfarcted myocardium was measured using inductively coupled MRI plasma atomic emission spectroscopy (ICP-AES). MRI without contras t media could not discern the MI. However, 3-24 h after injection of e ither Gd-MP or Mn-TPP, the infarcted area was positively stained MR im ages. This area matched well with the negative TTC-stained area on the heart slices (r = 0.97). The contrast ratios between the infarcted ne crotic myocardium and the noninfarcted regions varied from 150 to 300% depending on the type of agents and doses used. Neither false-positiv e nor false-negative findings were encountered. The metalloporphyrin c oncentration was more than 10 time higher in the infarcted than in the noninfarcted heart. Metalloporphyrins appear to be promising MRI cont rast agents for detection and quantification of necrosis in MI. These preclinical results may open new perspective in cardiac imaging.