Diffusion propagator metrics are biased when simultaneous multi-slice acceleration is used

TL;DR

This study investigates how simultaneous multi-slice (SMS) acceleration in diffusion MRI affects the accuracy of propagator metrics, revealing significant biases that depend on the SMS band number and acquisition parameters, impacting neuroimaging studies.

Contribution

It demonstrates that SMS acceleration introduces biases in MAP-MRI diffusion metrics, highlighting the need to account for these effects in quantitative brain imaging.

Findings

Zero-displacement and non-Gaussianity metrics are significantly affected by SMS.

Differences between SMS-2 and SMS-3 are statistically significant.

Bias characteristics change with shorter TR due to SMS acceleration.

Abstract

Advanced diffusion MRI models are being explored to study the complex microstructure of the brain with higher accuracy. However, these techniques require long acquisition times. Simultaneous multi-slice (SMS) accelerates data acquisition by exciting multiple image slices simultaneously and separating the overlapping slices using a mathematical model. However, this slice separation is not exact and leads to crosstalk between simultaneously excited slices. Although this residual leakage is small, it affects quantitative MRI techniques such as diffusion imaging. In this study, the effects of SMS acceleration on the accuracy of propagator metrics obtained from the MAP-MRI technique was investigated. Ten healthy volunteers were scanned with SMS accelerated multi-shell diffusion MRI acquisitions. Group analyses were performed to study brain regions typically affected by SMS acceleration. In addition, diffusion metrics from atlas based fiber tracts of interest were analyzed to investigate how propagator metrics in major fiber tracts were biased by 2- and 3-band SMS acceleration. Both zero-displacement metrics and non-Gaussianity metrics were significantly altered when SMS acceleration was used. MAP-MRI metrics calculated from SMS-3 showed significant differences with respect to SMS-2. Furthermore, when shorter TR afforded by SMS acceleration was used, the characteristics of this bias have changed. This has implications for studies using diffusion MRI with SMS acceleration to investigate the effects of a disease or injury on the brain tissues.