Cardiac metabolism measured noninvasively by hyperpolarized ¹³C MRI

Pyruvate is included in the energy production of the heart muscle and is metabolized into lactate, alanine, and CO(2) in equilibrium with HCO(3) (-). The aim of this study was to evaluate the feasibility of using (13)C hyperpolarization enhanced MRI to monitor pyruvate metabolism in the heart during an ischemic episode. The left circumflex artery of pigs (4 months, male, 29-34 kg) was occluded for 15 or 45 min followed by 2 hr of reperfusion. Pigs were examined by (13)C chemical shift imaging following intravenous injection of 1-(13)C pyruvate. (13)C chemical shift MR imaging was used in order to visualize the local concentrations of the metabolites. After a 15-min occlusion (no infarct) the bicarbonate signal level in the affected area was reduced (25-44%) compared with the normal myocardium. Alanine signal level was normal. After a 45-min occlusion (infarction) the bicarbonate signal was almost absent (0.2-11%) and the alanine signal was reduced (27-51%). Due to image-folding artifacts the data obtained for lactate were inconclusive. These studies demonstrate that cardiac metabolic imaging with hyperpolarized 1-(13)C-pyruvate is feasible. The changes in concentrations of the metabolites within a minute after injection can be detected and metabolic maps constructed.