Registration and Visualization of Transcranial Magnetic Stimulation on MR Images

Transcranial Magnetic Stimulation (TMS) has been widely used in the mapping of the primary motor cortex, as well as in the study of language, memory, mood, auditory or visual perception [4]. Similarly to EEG or MEG, it provides information Motor Evoked Potentials (MEP) located on the surface of the scalp and requires a registration between the physical space (PhS) and a MRI for proper interpretation. Several methods have been proposed for this registration. Wang [5] and Bastings [1] use a magnetic field (MF) digitizer to acquire points on the scalp surface. Wang attaches the MF transmitter on the patient’s head while Basting uses two receivers, one fixed on the patient to track head motion and one mobile to acquire the data. Bastings uses 6 MRI-visible landmarks for registration while Wang uses approx. 400 points for MRI to PhS registration, then landmarks for PhS to PhS registration in repeat experiments on the same patient. Ettinger [3] and Potts [4] use a combination of laser to digitize the head surface and optical tracking using LEDs to follow head motion. In this paper we propose a registration method based on Bastings’ and Wang’s, but that improves them both in terms of precision and ease of use.