Bias Introduced by Multiple Head Coils in MRI Research: An 8 Channel and 32 Channel Coil Comparison

Abstract

Neuroimaging MRI data in scientific research is increasingly pooled, but the reliability of such studies may be hampered by the use of different hardware elements. This might introduce bias, for example when cross-sectional studies pool data acquired with different head coils, or when longitudinal clinical studies change head coils halfway. In the present study, we aimed to estimate this possible bias introduced by using different head coils to create awareness and to avoid misinterpretation of results. We acquired, with both an 8 channel and 32 channel head coil, T1-weighted, diffusion tensor imaging and resting state fMRI images at 3T MRI (Philips Achieva) with stable acquisition parameters in a large group of cognitively healthy participants (n = 77). Standard analysis methods, i.e., voxel-based morphometry, tract-based spatial statistics and resting state functional network analyses, were used in a within-subject design to compare 8 and 32 channel head coil data. Signal-to-noise ratios (SNR) for both head coils showed similar ranges, although the 32 channel SNR profile was more homogeneous. Our data demonstrates specific patterns of gray and white matter volume differences between head coils (relative volume change of 6 to 9%), related to altered image contrast and therefore, altered tissue segmentation. White matter connectivity (fractional anisotropy and diffusivity measures) showed hemispherical dependent differences between head coils (relative connectivity change of 4 to 6%), and functional connectivity in resting state networks was higher using the 32 channel head coil in posterior cortical areas (relative change up to 27.5%). This study shows that, even when acquisition protocols are harmonized, the results of standardized analysis models can be severely affected by the use of different head coils. Researchers should be aware of this when combining multiple neuroimaging MRI datasets, to prevent coil-related bias and avoid misinterpretation of their findings.

Keywords: DTI; MRI; bias; gray matter; multicenter study; neuroimaging; white matter.

FIGURE 1

Color-coded SNR brain maps in the sagittal, axial and coronal direction for 8 channel head coil (8CH) and 32 channel head coil (32CH). Colorbar represents SNR values, ranging 0-85.

FIGURE 2

Voxel-based coil differences in panel (A) gray matter (GM) and (B) white matter volume (WM) using voxel-based morphometry paired sample t-tests on T1 weighted images. 8CH = 8 channel head coil, 32CH = 32 channel head coil. p values are color coded from 0.05 to <0.0001 FWE corrected.

FIGURE 3

Voxel-based coil differences in panel (A) fractional anisotropy (FA) and (B) mean diffusivity (MD) using tract-based spatial statistics paired sample t-test on diffusion weighted images. 8CH = 8 channel head coil, 32CH = 32 channel head coil. p values are color coded from 0.05 to <0.0001 FWE corrected.

FIGURE 4

Voxel-based coil differences in network-based functional connectivity using dual regression paired sample t-test on resting state fMRI images. 8CH = 8 channel head coil, 32CH = 32 channel head coil. (A–H) Represents standard resting state networks of interest, illustrated and named in green. p values are color coded from 0.05 to <0.0001 FWE corrected.