Intravoxel Fibre Structure of the Left Ventricular Free Wall and Posterior Left-Right Ventricular Insertion Site in Canine Myocardium Using Q-Ball Imaging

Abstract

Q-ball imaging (QBI) is an established high-angular resolution diffusion MRI technique enabling to resolve intravoxel fibre structure. Here, we present a detailed study of myocardial fibre orientation using QBI. We compare standard diffusion tensor MRI (DTI) versus QBI in the canine left ventricular free wall (LVFW) and posterior left-right ventricular insertion site. Most voxels within the LVFW show high fractional anisotropy (FA), Gaussian diffusion profiles, and a single population of aligned fibres. In these, the difference between fibre helix angles estimated by DTI and QBI is below 5°. However, we show that reduced FA near the anterior papillary muscle in the LVFW and in most of the left-right ventricular fusion site correlates with non-Gaussian diffusion. The QBI orientation distribution functions (ODF) in these regions reveal complex intravoxel fibrous structure, which cannot be inferred using DTI. Extensive ODF maps of myocardial fibre orientation are presented and discussed for the first time to our knowledge.