Microstructural Imaging with a Nonlinear Gradient: Pushing the Limit of Short Diffusion Time

Motivation: Locally high gradient strength from a nonlinear gradient paves a new way for microstructure MRI at short diffusion times well below 10ms, and the geometry of the nonlinear gradient suits skeletal muscle of lower extremities. Goal(s): To derive radial diffusivity of calf muscle at short diffusion times and derive the microstructure. Approach: We designed a diffusion encoding scheme integrating linear and nonlinear gradients, and developed Radial Diffusivity Imaging. We estimate surface-to-volume ratio from the radial diffusivity at short diffusion times. Results: With diffusion times as short as 4ms, the time-dependent radial diffusivity shows expected square-root time dependence, enabling quantification of calf muscle microstructure. Impact: With the high strength of nonlinear gradient, this study reveals time-dependent diffusivity of the calf muscle at short diffusion times, and sheds light on microstructure of the calf muscle non-invasively.