Hyperpolarized metabolic imaging of myocardial ischemia-reperfusion in a small-animal model at 9.4T

Abstract

Background Dynamic hyperpolarization (DNP) of Carbon-13 (13C) allows in-vivo assessment of metabolic processes. The aims of the present study were to establish a living rat model of ischemia-reperfusion and to study the metabolic changes in the myocardium following short periods of coronary artery occlusion using intravenous injection of hyperpolarized 1-13C pyruvate. Methods An inflatable balloon was secured around the left coronary artery of Sprague Dawley rats. 5-7 days after surgery rats were placed in a Bruker Biospec 9.4T small animal MR system. To enhance bicarbonate signal, animals received an iv glucose/potassium infusion. The tubing of the occluder was connected to extension tubing to allow occlusion while the animal remained in the bore of the MR system. A custom-built multi-sample DNP polarizer (1) was used to polarize samples (25.4 μ L[ 1- 13 C]-pyruvic acid and 13.5 mM trityl radical doped with 1.5 mM Dotarem). The rats were injected with 1.4 ml DNP solution at 4 time points: baseline, reperfusion directly after 15 minutes of coronary occlusion, after 30 minutes of reperfusion, after 60 minutes of reperfusion. A subgroup of rats underwent repeat imaging 1 week after ischemia. Metabolic data were acquired with a multiband pulse in combination with a multi-echo single-shot EPI readout (2). Hearts were removed and stained to delineate the area at risk (AAR), and for myocardial infarction. Results