Sensitivity to white matter FMRI activation increases with field strength.

Erin L Mazerolle,Jodie R Gawryluk,Kirk W Feindel,Aaron J Newman,M Tynan R Stevens,Kim N H Dillen,Steven D Beyea,Matthias H Schmidt,Steven A Patterson,Ryan C.N D’Arcy

doi:10.1371/journal.pone.0058130

Abstract

Functional magnetic resonance imaging (fMRI) activation in white matter is controversial. Given that many of the studies that report fMRI activation in white matter used high field MRI systems, we investigated the field strength dependence of sensitivity to white matter fMRI activation. In addition, we evaluated the temporal signal to noise ratio (tSNR) of the different tissue types as a function of field strength. Data were acquired during a motor task (finger tapping) at 1.5 T and 4 T. Group and individual level activation results were considered in both the sensorimotor cortex and the posterior limb of the internal capsule. We found that sensitivity increases associated with field strength were greater for white matter than gray matter. The analysis of tSNR suggested that white matter might be less susceptible to increases in physiological noise related to increased field strength. We therefore conclude that high field MRI may be particularly advantageous for fMRI studies aimed at investigating activation in both gray and white matter.

Highlights

Despite recent reports of white matter functional magnetic resonance imaging activation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15], the ability to detect fMRI signal changes in white matter remains controversial [15,16]
In addition to activation results, we examined temporal signal to noise ratio as a function of tissue type and field strength, as this metric has been linked to successful detection of fMRI activation (e.g., [35])
To determine whether activation on the white matter region of interest (ROI) likely originated from the posterior limb of the internal capsule (PLIC), we evaluated whether the activation on the PLIC ROI included local maxima

Summary

Introduction

Despite recent reports of white matter functional magnetic resonance imaging (fMRI) activation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15], the ability to detect fMRI signal changes in white matter remains controversial [15,16]. Increased field strength improves sensitivity to fMRI activation in two ways. The strength of the magnetic field perturbations produced by susceptibility differences is proportional to the strength of the applied field In this way, blood oxygen level dependent (BOLD) contrast (which depends on susceptibility differences caused by the relative concentration of diamagnetic oxygenated hemoglobin and paramagnetic deoxygenated hemoglobin) is improved at higher magnetic fields [17,32]. To evaluate the effect of field strength on sensitivity to white matter fMRI activation, we compared white matter activation during a finger tapping task at 1.5 T and 4 T. In addition to activation results, we examined temporal signal to noise ratio (tSNR) as a function of tissue type and field strength, as this metric has been linked to successful detection of fMRI activation (e.g., [35])

Methods

Results

Discussion

Conclusion