Quality assessment of MEG-to-MRI coregistrations

TL;DR

This study evaluates the quality of MEG-to-MRI coregistrations, proposing TRE as a more reliable metric than RMS residuals, and demonstrates the effectiveness of the Metropolis algorithm for improved coregistration accuracy.

Contribution

It introduces TRE as a new quality measure for coregistration and advocates for the Metropolis algorithm to enhance accuracy in MEG-to-MRI alignment.

Findings

Average TRE between 1.3 and 2.3mm at the head surface.

Metropolis algorithm significantly improves coregistration quality.

Sampled parameters enable TRE computation across MRI volume.

Abstract

For high precision in source reconstruction of magnetoencephalography (MEG) or electroencephalography data, high accuracy of the coregistration of sources and sensors is mandatory. Usually, the source space is derived from magnetic resonance imaging (MRI). In most cases, however, no quality assessment is reported for sensor-to-MRI coregistrations. If any, typically root mean squares (RMS) of point residuals are provided. It has been shown, however, that RMS of residuals do not correlate with coregistration errors. We suggest using target registration error (TRE) as criterion for the quality of sensor-to-MRI coregistrations. TRE measures the effect of uncertainty in coregistrations at all points of interest. In total, 5544 data sets with sensor-to-head and 128 head-to-MRI coregistrations, from a single MEG laboratory, were analyzed. An adaptive Metropolis algorithm was used to estimate the optimal coregistration and to sample the coregistration parameters (rotation and translation). We found an average TRE between 1.3 and 2.3mm at the head surface. Further, we observed a mean absolute difference in coregistration parameters between the Metropolis and iterative closest point algorithm of (1.9 $\pm$ 1.5){\deg} and (1.1 $\pm$ 0.9)mm. A paired sample t-test indicated a significant improvement in goal function minimization by using the Metropolis algorithm. The sampled parameters allowed computation of TRE on the entire grid of the MRI volume. Hence, we recommend the Metropolis algorithm for head-to-MRI coregistrations.