# On Using Signal Magnitude in Diffusion Magnetic Resonance Measurements of Restricted Motion

## TL;DR

This paper demonstrates that relying solely on signal magnitude in diffusion MRI leads to information loss, impairing accurate inference of tissue microstructure, especially near reflective boundaries.

## Contribution

It reveals the limitations of magnitude-based diffusion MRI models and highlights the importance of preserving phase information for microstructural analysis.

## Key findings

- Signal magnitude causes loss of Hermitian symmetry in diffusion MRI data.
- Loss of symmetry impairs microstructural inference near reflective boundaries.
- Simulation shows magnitude-based models are less accurate in complex geometries.

## Abstract

Tissue microstructure has significance as a biomarker, however its accurate inference with diffusion magnetic resonance (MR) is still an open problem. With few exceptions, diffusion weighted (DW) MR models either process diffusion MR data using signal magnitude, whereby microstructural information is forcefully confined to symmetry due to Fourier transform properties, or directly use symmetric basis expansions. Herein, information loss from magnitude utilization is demonstrated by numerically simulating particles undergoing diffusion near a fully reflective infinite wall and an orthogonal corner. Simulation results show that the loss of the Hermitian property when using signal magnitude impedes DW--MR from accurately inferring microstructural information in both of the geometries.