Toward faster inference of micron-scale axon diameters using Monte Carlo simulations

Abstract

Recent advances have allowed oscillating gradient (OG) diffusion MRI to infer the sizes of micron-scale axon diameters. Here the effects on the precision of the inferred diameters are studied when reducing the number of images collected to reduce imaging time for clinical feasibility. Monte Carlo simulations of cosine OG sequences (50-1000Hz) using a two-compartment model on a parallel cylinder (diameters 1-5μm) geometry were conducted. Temporal diffusion spectroscopy was used to infer axon diameters. Three different gradient sets were simulated with different combinations of gradient strengths. Five frequencies were adequate for d=3-5μm with single-sized cylinders and for effective mean axon diameters greater than 2μm for cylinders with a distributions of diameters. There was some improvement in precision for d=1-2μm with 10 frequencies. It is better to repeat measurements at higher gradient strengths than to use a range of gradient strengths. The improvement tended to be greatest when using fewer frequencies and was especially noticeable at very high gradient strengths. Images can be collected with fewer gradient strengths and frequencies without sacrificing the precision of the measurements. This could be useful in reducing imaging time so that OG techniques can be used in clinical settings.