An increased precision comparison of TMS-induced motor cortex BOLD fMRI response for image-guided versus function-guided coil placement.
OBJECTIVE
To examine with high precision the differences between function-guided and image-guided transcranial magnetic stimulation (TMS).


METHODS
Using a calibrated TMS coil holder/positioner, interleaved TMS/functional magnetic resonance imaging (fMRI), and individualized anatomy-based regional normalization, we conducted a two-phase study of TMS coil positioning guided by either function (elicited thumb motion) or image-based targeting of the "hand knob," the anatomy associated with fMRI activation during thumb motion.


RESULTS
In every case, image-guided TMS coil placement produced a thumb movement response at thresholds similar to those found under function guidance. Unexpectedly, function-guided coil locations clustered bimodally over central and precentral sulci. Image-guided locations clustered as anticipated toward the targeted gyral crown. Despite these differences, blood oxygenation level-dependent (BOLD) activation locations and magnitude for the two methods displayed no consistent differences in mean or variance between or within subjects. Image guidance produced more consistent coil placement from subject to subject relative to targeted anatomy. Surprisingly, BOLD time courses from image-guided experiments showed significantly slower return to baseline after TMS than was observed under function guidance.


CONCLUSIONS
The results demonstrate the effectiveness and precision of image-guided positioning of TMS coils combined with a precisely adjustable holder/positioner and regional normalization. Image guidance provides an accurate TMS placement relative to individual anatomy when no external sign is available.
Denslow
Stewart
S
Department of Radiology, Center for Advanced Imaging Research and Brain Stimulation Laboratories, Medical University of South Carolina, Charleston, South Carolina 29425, USA. denslows@musc.edu
Bohning
Daryl E
DE
Bohning
Peter A
PA
Lomarev
Mikhail P
MP
George
Mark S
MS
D000328:Adult; D002138:Calibration; D004599:Electric Stimulation Therapy / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D038361:Neuronavigation / Q000295:instrumentation* / Q000379:methods*