Individualized Template MRI Is a Valid and Reliable Alternative to Individual MRI for Spatial Tracking in Navigated TMS Studies in Healthy Subjects

Abstract

Objectives: Navigated transcranial magnetic stimulation (nTMS) provides significant benefits over classic TMS. Yet, the acquisition of individual structural magnetic resonance images (MRI individual ) is a time-consuming, expensive, and not feasible prerequisite in all subjects for spatial tracking and anatomical guidance in nTMS studies. We hypothesize that spatial transformation can be used to adjust MRI templates to individual head shapes (MRI warped ) and that TMS parameters do not differ between nTMS using MRI individual or MRI warped .Materials and Methods: Twenty identical TMS sessions, each including four different navigation conditions, were conducted in 10 healthy subjects (one female, 27.4 ± 3.8 years), i.e., twice per subject by two researchers to additionally assess interrater reliabilities. MRI individual were acquired for all subjects. MRI warped were obtained through the spatial transformation of a template MRI following a 5-, 9-and 36-point head surface registration (MRI warped_5 , MRI warped_9 , MRI warped_36 ). Stimulation hotspot locations, resting motor threshold (RMT), 500 µV motor threshold (500 µV-MT), and mean absolute motor evoked potential difference (MAD) of primary motor cortex (M1) examinations were compared between nTMS using either MRI warped variants or MRI individual and non-navigated TMS.Results: M1 hotspots were spatially consistent between MRI individual and MRI warped 36 (insignificant deviation by 4.79 ± 2.62 mm). MEP thresholds and variance were also equivalent between MRI individual and MRI warped_36 with mean differences of RMT by −0.05 ± 2.28% maximum stimulator output (%MSO; t (19) = −0.09, p = 0.923), 500 µV-MT by −0.15 ± 1.63%MSO (t (19) = −0.41, p = 0.686) and MAD by 70.5 ± 214.38 µV (t (19) = 1.47, p = 0.158). Intraclass correlations (ICC) of motor thresholds were between 0.88 and 0.97.Conclusions: NTMS examinations of M1 yield equivalent topographical and functional results using MRI individual and MRI warped if a sufficient number of registration points are used.

Disruption to left inferior frontal cortex modulates semantic prediction effects in reading and subsequent memory: Evidence from simultaneous TMS-EEG

“…Therefore, a successful registration relies on reliable mapping between individual anatomy and the group-based template. Indeed, while individualized anatomical mapping is the gold standard, recent evidence suggests that templatebased MNI localization can be used as an accurate and effective alternative to individualized anatomical localization for TMS studies (Fleischmann et al, 2020). Perhaps more importantly, given that the functional organization of LIFC can vary substantially from individual to individual as discussed above (Mahowald & Fedorenko, 2016;Fedorenko et al, 2012), a need for individualized functional localizers is critical for future research, arguably more so than individualized anatomical targeting.…”

Disruption to left inferior frontal cortex modulates semantic prediction effects in reading and subsequent memory: Evidence from simultaneous TMS‐EEG

“…Therefore, a successful registration relies on reliable mapping between individual anatomy and the group‐based template. Indeed, while individualized anatomical mapping is the gold standard, recent evidence suggests that template‐based MNI localization can be used as an accurate and effective alternative to individualized anatomical localization for TMS studies (Fleischmann et al, 2020). Perhaps more importantly, given that the functional organization of LIFC can vary substantially from individual to individual as discussed above (Mahowald & Fedorenko, 2016; Fedorenko et al, 2012), a need for individualized functional localizers is critical for future research, arguably more so than individualized anatomical targeting.…”

Physiological symmetry of transcranial magnetic stimulation‐evoked EEG spectral features

“…We checked that the use of individual MRI versus MRI template did not affect the natural frequency variability, although it may have affected the variability of the first component amplitude. Recent findings have suggested that brain responses to TMS can be equivalent when using an MRI template if a sufficient number of registration points are used during the curvilinear reconstruction of the participant's head (Fleischmann et al, 2020 ).…”