Reduction of bias in the evaluation of fractional anisotropy and mean diffusivity in magnetic resonance diffusion tensor imaging using region-of-interest methodology

Youngseob Seo,Nancy K Rollins,Zhiyue J Wang

doi:10.1038/s41598-019-49311-w

Abstract

Accurate quantification of fractional anisotropy (FA) and mean diffusivity (MD) in MR diffusion tensor imaging (DTI) requires adequate signal-to-noise ratio (SNR) especially in low FA areas of the brain, which necessitates clinically impractical long image acquisition times. We explored a SNR enhancement strategy using region-of-interest (ROI)-based diffusion tensor for quantification. DTI scans from a healthy male were acquired 15 times and combined into sets with different number of signal averages (NSA = 1–4, 15) at one 1.5-T Philips and three 3-T (Philips, Siemens and GE) scanners. Equivalence test was performed to determine NSA thresholds for bias-free FA and MD quantifications by comparison with reference values derived from images with NSA = 15. We examined brain areas with low FA values including caudate nucleus, globus pallidus, putamen, superior temporal gyrus, and substructures within thalamus (lateral dorsal, ventral anterior and posterior nuclei), where bias-free FA is difficult to obtain using a conventional approach. Our results showed that bias-free FA can be obtained with NSA = 2 or 3 in some cases using ROI-based analysis. ROI-based analysis allows reliable FA and MD quantifications in various brain structures previously difficult to study with clinically feasible data acquisition schemes.

Highlights

Magnetic resonance diffusion tensor imaging (DTI) provides information about water diffusion with the dominant direction parallel to the axonal orientation within the voxel of interest[1,2,3]
signal-to-noise ratio (SNR) and Intra-ROI diffusion direction dispersion angle (IRDDDA). Both SNR and IRDDDA values were estimated in the selected regions of the brain in terms of number of signal average (NSA) for four different MRI scanners (Fig. 1)
For lower SNR, this problem is more pronounced in low fractional anisotropy (FA) areas of the brain than high FA regions[14]

Summary

Introduction

Magnetic resonance diffusion tensor imaging (DTI) provides information about water diffusion with the dominant direction parallel to the axonal orientation within the voxel of interest[1,2,3]. In a previous work[14], on the other hand, it has been determined that bias free measurement of FA in the low FA region (putamen) at 1.5 T and 3 T requires at least number of signal average (NSA) = 9 and 6, respectively. We investigated an ROI-based tensor processing method in which image intensities inside an ROI with uniform diffusion properties are averaged first before calculating the diffusion tensor[17,18]. This method mitigates the requirement of long image acquisition times needed for bias-free FA and MD measurements and has not been applied to brain studies previously

Methods

Results

Conclusion