Transcranial Magnetic Stimulator
 
By:  Lisa Lim and Matthew Yee
Supervised by:  Dr. Tomas Paus - Neuropsychology, McGill University

   Please let us know first if you wish to reproduce any of the work on this website.


   TMS coils come in all types of designs.  Research into the design and construction of new TMS coils is rapidly growing.  In the follwing studies, the TMS coils under investigation are of three designs.  I have included photographs of these coils for your convenience.

   The most simplest design is the circular TMS coil.  A photograph of the circular TMS coil is shown below with the corresponding x-ray image.  The circular TMS coil contains 14 windings of copper bands.

 
The circular coil. An X-ray of the top of the circular coil. An X-ray of the side of the circular coil.

(Click on image to see a larger picture.)
   The next design is the Figure-eight TMS coil which consists of two lobes. The current in the lobes are such that the current down the center of the Figure-eight TMS coil is in the same directuib.   It is contained in a wooden casing in Dr. Paus' Laboratory.  The wooden casing also contains an air cooling system which is used to prevent overheating of the TMS coil during use.  The photograph of the exterior of the Figure-eight TMS coil is shown below with it's corresponding x-ray image.  The Figure-eight TMS coil also contained 14 windings of copper bands.
The figure-8 coil. An X-ray of the coil. The coil's width profile. The length profile.

(Click on image to see a larger picture.)
   The last TMS coil design studied here is the Cone TMS coil.  It is basically the same as the Figure-eight TMS coil but the two lobes are at an angle of 73 degrees rather than in one plane.  The arrows in the photograph indicate the direction of the current in the two lobes.
The conical coil.  The profile of the coil. The X-ray  from above. 

(Click on image to see a larger picture.)
The following pages contain some of the results of the work done on various designs of the TMS coil.

1 Transcranial Magnetic Stimulator:  The 3-Dimensional Mapping of the Magnetic Field
     The magnetic field distribution for the Figure 8 TMS coil was investigated both theoretically and experimentally.  Theoretical simulations of the magnetic field correlated quite well with the actual measurements.  The simulation programs were written in C and can be found on this page.  Details regarding the experimental procedure are also found on this page.

2  Work in Progress
     The magnetic field distribution for the Figure 8 TMS coil, the Cone TMS coil, and the Circular TMS coil were investigated theoretically and experimentally following the same procedure found in the previous investigation.  The theoretical simulations for the Cone TMS coil were unsuccessful due to the nature of the problem.  A new subroutine must be written to complete this task.

You can also get more information on TMS by visiting:
Dr. Tomas Paus -  McConnell Brain Imaging Centre
Montreal Neurological Institute
McConnell Brain Imaging Center at McGill University
Cadwell - United State of America (manufacturer)
MagStim - U.K. (manufacturer)
Transcranial Magnetic Stimulation - Helsinki, Finland
Groups working on TMS
Please email us with any suggestions, comments or questions at:  llim@bottom.bic.mni.mcgill.ca and myee@bottom.bic.mni.mcgill.ca       Last Updated:  September 18, 1999.