# A comparison of fMRI presurgical mapping techniques with intraoperative brain mapping-based validation

## TL;DR

This study compares resting-state and task-based fMRI techniques for presurgical brain mapping using intraoperative validation, finding similar accuracy for both methods.

## Contribution

The study validates rsfMRI as a viable alternative to task-based fMRI for presurgical mapping using intraoperative electrical stimulation as ground truth.

## Key findings

- Resting-state fMRI showed comparable accuracy to task-based fMRI for sensory-motor mapping.
- Multiecho rsfMRI had slightly lower accuracy than single-echo rsfMRI at larger voxel sizes.
- Differences in accuracy between methods were minor when using the same distance cutoffs.

## Abstract

Resting-state functional MRI (rsfMRI) could enable preoperative risk assessment and intraoperative guidance for patients who cannot undergo task-based fMRI (tbfMRI). To ascertain rsfMRI’s applicability, we investigated differences in accuracy between tbfMRI with a voxel size of 1.8 x 1.8 x 3.2 mm³ and rsfMRI acquired with single-echo (sTE) with a voxel size of 2 x 2 x 2.2 mm³ and multiecho (mTE) with a voxel size of 3 x 3 x 3 mm³ using intraoperative mapping with direct electrical stimulations (DES) as the ground truth. Functional sensory-motor mapping results of hands and feet were spatially compared relative to positive (pDES, functional effect) and negative (nDES, no functional effect) coordinates in 16 preoperative patients. A general linear model analysis was used for tbfMRI, and seed-based analysis (SBA) for rsfMRI. Minimum Euclidean distances between fMRI and DES were calculated and compared between fMRI methods. Receiver-operating characteristic (ROC) curves were used to compare accuracy and determine distance cutoffs for fMRI agreement with DES, and binary agreement rates were compared at different cutoffs. Two-part mixed-effects linear models were used to compare fMRI methods while accounting for unequal intersubject DES repetition. Only minor differences were found between fMRI methods in unthresholded distances (mean differences ~2 mm). ROCs and binary agreement measures showed comparable accuracy for tbfMRI and sTE-rsfMRI at 2 mm, but mildly worse for sTE-rsfMRI at 3 mm and mTE-rsfMRI. However, differences in relative accuracy between sTE-rsfMRI and mTE-rsfMRI were minor when the same distance cutoff was applied to all methods. This was also reflected in comparing binary agreement rates and confirmed by the two-part linear models, which showed no significant differences between fMRI methods and a significant effect of DES response. A similar accuracy for SBA rsfMRI functional sensory-motor mapping compared with tbfMRI for the hands and feet indicates that rsfMRI may be suitable for presurgical mapping. The differences in relative accuracy between sTE-rsfMRI and mTE-rsfMRI warrant further investigation in a larger sample.