Three‐dimensional ³¹P magnetic resonance spectroscopic imaging of regional high‐energy phosphate metabolism in injured rat heart

Abstract

The purpose of this study was to measure the spatially varying 31P MR signals in global and regional ischemic injury in the isolated, perfused rat heart. Chronic myocardial infarcts were induced by occluding the left anterior descending coronary artery eight weeks before the MR examination. The effects of acute global low-flow ischemia were observed by reducing the perfusate flow. Chemical shift imaging (CSI) with three spatial dimensions was used to obtain 31P spectra in 54-microl voxels. Multislice 1H imaging with magnetization transfer contrast enhancement provided anatomical information. In normal hearts (n = 8), a homogeneous distribution of high-energy phosphate metabolites (HEP) was found. In chronic myocardial infarction (n = 6), scar tissue contained negligible amounts of HEP, but their distribution in residual myocardium was uniform. The size of the infarcted area could be measured from the metabolic images; the correlation of infarct sizes determined by histology and 31P MR CSI was excellent (P < 0.006). In global low-flow ischemia (n = 8), changes of HEP showed substantial regional heterogeneity. Three-dimensional 31P MR CSI should yield new insights into the regionally distinct metabolic consequences of various forms of myocardial injury.

Xanthine oxidase inhibitors improve energetics and function after infarction in failing mouse hearts

“…The improvement in cardiac PCr/ATP with XOI is not likely due to an effect on infarct size because it is similar in control and infarcted hearts (Ref. 43, and see RESULTS) and because infarcted tissue does not contain significant PCr or ATP (45,48). XOI is one of the first metabolic interventions that normalize reduced cardiac energetics in any model of heart failure.…”

“…The PCr/ATP values were corrected for partial saturation effects using a factor determined in separate studies (6,8,46,47) that included fully relaxed acquisitions. Infarcted, nonviable myocardium lacks PCr and ATP (45,48). In prior 31 P MRS studies (16,18,19,32,33,37) of infarcted rodent hearts, the detected PCr and ATP signals were attributed to the surviving viable regions, even when the entire infarcted region was contained within the region studied by MRS. Based on this accepted practice and our efforts through animal positioning and slice selection to minimize infarcted tissue within the volume of interest, the cardiac PCr/ATP values reported here derive almost entirely from surviving, viable myocardium.…”

Fast High-Resolution Magnetic Resonance Imaging Demonstrates Fractality of Myocardial Perfusion in Microscopic Dimensions

“…Because the perfusionsensitive T 1 map is obtained in Ͻ40 seconds, we achieve a high temporal resolution that allows us to study the dynamics of heterogeneity in future projects. The perfusion imaging technique can be combined with metabolic 26 and oxygenation 22 sensitive imaging, which will provide further insight into the origin of heterogeneity of myocardial blood flow.…”

Three-Dimensional 13C-Spectroscopic Imaging in the Isolated Infarcted Rat Heart

“…The infarct size was determined histologically as previously described (17). After MR imaging, the infarcted hearts were embedded in paraffin and cut in 20-m sections (slice separation 1 mm).…”

“…For anatomical information 1 H-images were acquired with a modified FLASH sequence (17,20). The matrix size was 256 ϫ 256 with a slice thickness of 1 mm.…”