Segmental analysis of cardiac metabolism by hyperpolarized [1-13C] pyruvate: an in-vivo 3D MRI study in pigs

Methods Seven male pigs (38±2 kg) were imaged on a 3T MRI scanner (GE Excite Hdx) with a 13C birdcage coil. 13C-pyruvate (20mL of 230mM) was hyperpolarized using a Dynamic Nuclear Polarization technique (Hypersense) and injected in pigs at rest and during occlusion of the left anterior descending coronary artery. Anatomical reference images were acquired by a standard SSFP sequence. Metabolic information were obtained using a volumetric IDEAL spiral CSI sequence [4] prescribed on the same region imaged by the reference anatomical sequence (FOV 30x30x10cm, TE=0.9ms, FA=7°), after 20 sec from the injection starting. 3D axial volumes were reconstructed for Pyruvate, Lactate, and Bicarbonate metabolites. Short axis (SA) cardiac views were reformatted by PMOD software by using the anatomical images as reference. Quantitative analysis was performed on SA views by custom (HIPPO-C13) software developed in IDL 8.0. Myocardial contours were manually defined in anatomical SA views covering the LV (Fig 1.A) A reference point corresponding to superior insertion of the right ventricle wall was defined. Slices were classified as basal, middle, or apical by the operator. Starting from the reference point, myocardium was divided in six (basal and medium slices) or four (apical slices) equiangular segments. Corresponding polar maps were extracted as illustrated in Fig. 1.B. Values of metabolites signal in corresponding segment of basal, middle, and apical slices were averaged leading to a 16-segments model of metabolite distribution, following AHA guidelines [3] (Fig 1.C).