Abstract
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Objectives: Combination of PET and MRI may give insights into cardiac pathophysiology by providing integrated information on biology and morphology. We sought to determine the feasibility of PET and MRI assessment of the healthy and infarcted rat heart.
Methods: In 14 male Wistar rats, PET and MRI studies were performed before and after transmural myocardial infarction with ligation of left coronary artery. [N-13]ammonia-PET and [F-18]FDG-PET were performed to assess perfusion and insulin-stimulated regional glucose metabolism with 3D acquisition mode in a small-animal PET system (Mosaic, Philips). Cine-MRI was performed on a 1.5T clinical system (Sonata, Siemens) with a dedicated small animal ECG triggering device and a small surface coil. Additionally, to determine the infarcted area, the late enhancement MR images using Gd-DTPA were obtained. MRI and PET images were coregistered.
Results: Left ventricular ejection fraction in normal rats measured by MRI was 57+/-2.6%, and decreased to 39+/-10% (p<0.001) following myocardial infarction. In normal rats, regional [F-18]FDG uptake, perfusion and MRI-derived wall thickness were almost homogeneous throughout the left ventricle. FDG uptake showed mild heterogeneity with lowest mean uptake in apex (79.3+/-6.0) and highest in the basal anterior segment (93.6+/-4.3). In disease model, the infarct size was determined by the ratio of the defect area on the total area of the myocardium. The [F-18]FDG uptake defect was defined as area below - 5SD of the mean values of a normal rat group. The infarct size determined by [F-18]FDG PET was well correlated with the infarct size derived from delayed enhancement MRI (r = 0.88), the infarct size obtained with ex vivo [F18[FDG autoradiography (r = 0.83) and the infarct size determined by [N13]ammonia perfusion PET (r = 0.87).
Conclusions: Combination of MRI and PET allows for the quantitative assessment of multiple cardiac tissue parameters in the animal model. Correlation with ex vivo measurements revealed high accuracy of imaging to determine tissue viability and necrosis. Thus, multimodality small animal imaging is promising to study molecular interventions longitudinally.
- Society of Nuclear Medicine, Inc.