Symmetric Multimodal Mapping of Ex Vivo Cardiac Microstructure of Large Mammalian Whole Hearts for Volumetric Comparison of Myofiber Orientation Estimated from Diffusion MRI and MicroCT.

Description of the cardiac myofiber architecture in pathological or even physiological conditions is essential for image-based modeling in electrophysiology or mechanical studies. While diffusion tensor imaging (DTI) is one of the best modalities to capture myofiber orientation of large mammalian hearts, validations of putative myofiber’s main orientation from DTI in whole hearts of large mammals is limited. First we design an experimental protocol for sheep (N = 1) and human (N = 1) whole hearts that combine a standardized sample preparation with high-resolution diffusion MRI at 600 µm 3 using low angular resolution (6 directions) followed by a tissue air-drying approach coupled with X-ray imaging at 42 µm 3 . Secondly, we propose a standardized post-processing pipeline for symmetric multimodal mapping allowing the comparison of myofiber orientation computed from DTI and structure tensor imaging (STI), respectively. We then identified region-of-interest (ROI) exhibiting small or sharp spatial variations in myofiber orientation and compared the putative myofiber orientation for both methods. In conclusion, we show a good correspondence of structural features between the two imaging modalities and identify new unexpected and complex cardiomyocytes organization such as oscillating patterns or clear separation of opposing fiber-bundles.