Calculation of Lorentz Forces on Coils for Transcranial Magnetic Stimulation During Magnetic Resonance Imaging

New applications for transcranial magnetic stimulation (TMS) are rapidly being developed for diagnostic and therapeutic purposes but are restricted by a number of technical limitations. The ability to reliably perform TMS concurrently with functional magnetic resonance imaging (fMRI) would be a valuable tool for researchers. However the forces experienced by TMS coils during normal operation due to large transient magnetic fields which are produced, are problematic. When operated within a large external field, such as in an fMRI scanner these forces can result in mechanical failure of the coils. This paper presents calculations of these forces to form a basis from which coil failure can be prevented.