Brain-Imaging-Center / TMS-fMRI

Technical developments for simultaneous TMS-fMRI
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How much does the 3 T change the impedance of the TMS coil? #14

Open BenInglis opened 8 years ago

BenInglis commented 8 years ago

Standard procedure is to establish a motor threshold outside the MRI and then use this stimulus intensity level to calibrate the intended use of the TMS elsewhere in the brain. The presence of the magnetic field will change the impedance for the TMS coil and will alter the temporal characteristics of the TMS pulses, compared to behavior in negligible magnetic field. Is there a systematic difference in the stimulus intensity required for the motor threshold inside versus outside the magnet, for the same subjects?

DobyRahnev commented 8 years ago

This issue has already been addressed experimentally by Yau et al. (2014). Static Field Influences on Transcranial Magnetic Stimulation: Considerations for TMS in the Scanner Environment. Brain Stimulation.

They found that TMS inside the bore is very similar to TMS outside the scanner room. Interestingly, there are major changes when delivering TMS right outside the bore but we never do that anyway.

BenInglis commented 8 years ago

Thanks. We should redo these tests since they used Magstim hardware rather than Magpro. The Magstim product we once tested in the Varian 4 T was totally different than Magpro, causing massive dropout and sounding like a shotgun when the TMS pulses were discharged. Unsurprisingly, the coil cracked and was retired from service after not very many pulses.