Mapping crossing myofiber populations with Diffusion Spectrum Imaging in simulated and microfabricated model tissues

Abstract

The ability to resolve complex myofiber populations is important for relating architectural structure with mechanical unction in muscular tissues. To address this issue, we sought to validate the capacity of Diffusion Spectrum Imaging (DSI), an MRI method for assessing molecular diffusion in a confined geometry, to determine fiber alignment in tissues whose myofibers are aligned at varying orientations. By this method, molecular displacement in a tissue can be determined by Fourier transforming the echo intensity against gradient strength at fixed gradient pulse spacing. The displacement profiles are visualized by graphing 3D isocontour icons for each voxel, with the isocontour shape and size representing the magnitude and direction of the constituting fiber populations. Validation of DSI was accomplished with two sets of experiments: We simulated diffusive motion and a DSI experiment within the constraints of crossing fibers, and determined that DSI accurately depicts arbitrary angular relationships between crossing fibers. We also used DSI to accurately resolve the geometry of aligned channels in poly(dimethylsiloxane) (PDMS) microfluidic phantoms.