MRI with necrosis-avid contrast agent for the assessment of myocardial viability in a swine model

Objective: To determine the relationship between the delayed enhanced area on MRI revealed with necrosis-avid contrast agent (NACA) bis-Gd-DTPA-pamoic acid derivative (EC III-60) and the infarction area on pathologic examination, and compare it with an extracellular agent Gd-DTPA after intravenous injection. Methods: The reperfused myocardial infarction model was created by minimally invasive close-chest method in eight pigs. After intravenous injection of Gd-DTPA (0.2 mmol/kg), all pigs were kept scanning with T₁-weighted imaging until lesion enhancement vanished. Then they were intracoronarily infused with EC III-60 (0.0025 mmol/kg) and imaged for 5 hrs. The extent of delayed enhanced area on EC III-60 enhanced MRI was compared and correlated with TTC stained sections. Contrast ratio (CR) and relative infarct size (RIS) were quantified and compared with those of Gd-DTPA enhanced MRI. Results: CR over 3.0 was obtained and it persisted over 5 hfs on EC III-60 enhanced MRI. The spatial extent of delayed enhanced area (11.84 ± 3.63)% was consistent with the spatial extent of infarction area (11.78±3.64)% (t=2.251, P>0.05). There was excellent correlation between the lesion size on EC III-60 enhanced T₁-weighted MR images and histomorphometry (r=0.999, P<0.01). CR over 3.0 was also induced by Gd-DTPA, however, the enhancement vanished gradually in 2 hrs. Conclusions: NACA can demarcate the myocardial infarction persistently and accurately. It is a potential method for postprocedural assessment of myocardial viability after coronary interventions. (authors)