Diffusion tensor imaging (DTI) is a magnetic resonance (MR) imaging technique that has attracted attention in recent years for applications such as nerve fiber tracking, neurography, and tumor detection. In DTI measurements, 2 motion-probing gradient (MPG) pulses are applied to evaluate water diffusion. In DTI for nerve fiber tracking, acquisition parameters, such as strength, duration, and separation of MPGs, influence the MR signal.
In this study, we set acquisition parameters in DTI to emphasize fractional anisotropy to clarify the direction of nerve fibers. We performed Monte Carlo simulations of restricted diffusion in a cylinder model and phantom measurements with capillary plates to examine the relationship between the acquisition parameters in DTI and the size of restricted structures, particularly their diameter and length, which we will refer to as "compartment size."
We confirmed that normalized signal intensities in DTI measurements depend on diffusion time, which, in turn, depends on the separation and duration of the MPG, and they decrease with increase in compartment size. Furthermore, our simulation and phantom results suggest that use of a longer diffusion time effectively emphasizes fractional anisotropy to clarify the direction of nerve fibers.