Measurement of axon radii distribution in orientationally unknown tissue using angular double-pulsed gradient spin echo (double-PGSE) NMR

Introduction We present an analytical diffusion model for measuring axon radii distribution in orientationally unknown tissue using angular d-PGSE NMR. S-PGSE NMR reflects the underlying axon properties that restrict internal diffusion. Estimating these properties using s-PGSE, however, requires prior knowledge of tissue orientation and high q-values, inhibiting clinical application of these methods[1]. Emerging methods for estimating orientationally invariant fibers using s-PGSE requires protocol optimization for the specific axon radius being estimated[2]. Our simulation results are the first to demonstrate that using angular d-PGSE experiments, clinically feasible acquisition is sufficient to accurately reconstruct quantitative measurements of axon properties in tissue of unknown orientation in typical human brain tissue range ) 5 1 ( m μ − . In addition to axon radii distribution, we were also able to infer other important axon properties such as axon orientation and axon volume fraction. Method Imaging Protocol The double-PGSE sequence is the simplest form of multi-PGSE, first proposed by Cory. Two pairs of diffusion gradients 1 G and 2 G are applied at any direction with angle ψ between them. The two encoding intervals are separated by mixing