Visualization of subcortical language pathways by diffusion tensor imaging fiber tracking based on rTMS language mapping

Abstract

Diffusion tensor imaging fiber tracking (DTI FT) is used to visualize subcortical fiber tracts. Yet, there is no standard at hand to visualize language-involved subcortical fibers reliably. Thus, this study investigates the feasibility of using language-related cortical areas identified via repetitive navigated transcranial magnetic stimulation (rTMS) to seed DTI FT of subcortical language tracts. From 2011 to 2014, 37 patients with left-hemispheric perisylvian lesions were examined. Language-positive rTMS stimulation spots were integrated in the deterministic tractography software (BrainLAB, iPlanNet 3.0) as objects and used as seed regions for DTI FT. Tractography was then performed in each patient with 77 different combinations of fiber lengths (40 - 100 mm) and fractional anisotropy (FA; 0.01 - 0.5). The rTMS-based DTI FT identified all commonly known subcortical language tracts, such as the corticonuclear tract, arcuate fascicle, uncinate fascicle, superior longitudinal fascicle, inferior longitudinal fascicle, arcuate fibers, commissural fibers, corticothalamic fibers, and the fronto-occipital fascicle. In 32 patients (86.5 %), each above-named tract could be visualized, while at least 6 out of these 9 tracts were identified in each patient. A fiber length of 100 mm and an FA of 0.1 or 0.15 provided optimal visualization by revealing 125 and 61 individually tracked fibers per visualized language tract and 90 % and 73 % of all language-related tracts, respectively. This study proves the feasibility of rTMS-based DTI FT for subcortical language tracts, provides suitable settings, and shows its easy and standardizable application for the visualization of every language tract in 86.5 % of patients.

Specific DTI seeding and diffusivity-analysis improve the quality and prognostic value of TMS-based deterministic DTI of the pyramidal tract

“…Varying values of adjusted FA values can lead to varying tracking results where the ROIs' location highly influences them, reflecting differences in local FA values ( Frey et al, 2012 , Negwer et al, 2016 , Negwer et al, 2017 , Weiss et al, 2015 ). Therefore we analyzed tractography results performed with the specific plane ROI and different FA values (0.01, 0.05, 0.1, 25% of FAT, 50% of FAT and 75% of FAT) in terms of plausibility and tractography parameters described above to identify the optimal tracking algorithm for the preoperative evaluation.…”

The verb and noun test for peri-operative testing (VAN-POP): standardized language tests for navigated transcranial magnetic stimulation and direct electrical stimulation

“…TMS cannot map the subcortical white matter fiber tracts that need to be identified with intraoperative DES. However, the combined use of nTMS and tractography has been recently described to obtain a preoperative mapping of the language network [28,36,38]. Having a preoperative map of the functional boundaries depicted by nTMS then leads to a shorter intraoperative procedure [31], a more targeted craniotomy [37] and more confidence in decision making for the surgical team.…”

Associations between clinical outcome and navigated transcranial magnetic stimulation characteristics in patients with motor-eloquent brain lesions: a combined navigated transcranial magnetic stimulation–diffusion tensor imaging fiber tracking approach

“…This is in line with the findings of a previous study on nTMS-based DTI FT of language pathways. 31 In this context, other methods, such as high angular resolution diffusion imaging, are currently being promoted for tractography purposes, with promising results. Yet, they are still not routinely applied in most neurosurgical centers because they represent much more elaborate approaches, which can hamper integration into the workflow of clinical routine.…”