A hemiparetic stroke may lead to changes in muscle structure that further exacerbate motor impairments of the paretic limb. Cadaveric measurements have previously been used to study structural parameters in skeletal muscles but has several limitations, including ex vivo fixation. Here, we present novel application of diffusion tensor imaging (DTI) based probabilistic tractography methods, in comparison to the traditional deterministic approach, with respect to cadaveric dissection to quantify in vivo muscle fascicles in the biceps brachii. Preliminary results show that probabilistic tractography yields longer fascicle lengths that are more consistent with cadaveric measurements, albeit with higher variability, while deterministic tractography identifies shorter fascicle lengths, but with less variability. Results suggest that DTI tractography techniques can capture fascicles consistent with previously published cadaveric measurements and can identify interlimb differences in fascicle lengths in an individual with stroke.Clinical Relevance - The methods proposed here describe a non-invasive way to quantify heterogeneous musculoskeletal parameters such as across upper arm muscles in individuals with hemiparetic stroke. This will expand the current knowledge of macro- and micro-structural muscle changes that occur after stroke and may lead to more effective rehabilitation strategies to prevent such changes in individuals with stroke.