Implementation of a System for Real Time Space Localization of Cerebral Regions for TMS Application by MRI Co-Register

Author(s)

André Salles Cunha Peres

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2008-04-11

Examining board members

Oswaldo Baffa Filho; Ernane José Xavier Costa; Claudia Domingues Vargas

• Advisor: Oswaldo Baffa Filho

Abstract

In the last 20 years we witnessed a great advance in neurosciences and evaluation techniques as an initial attempt for understanding of working principles of the human central nervous system Techniques such as electroencephalography (EEG), positron emission tomography (EEG), functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) have produced grate advances in the understanding of human cerebral nervous system. fMRI generates statistical maps of the cerebral activity and TMS uses intense and fast magnetic pulses to produce a high rate magnetic flux variation to produce cortical electrical stimulation. However, even today TMS uses subjective parameters to establish an area responsible for a certain stimulated activity, that does not allow the precise cortical localization of the cortex area being stimulated by the magnetic pulse. Aiming to overcome this subjectiveness to more precisely stimulate the activity center this work investigates the use of a co-register method based on TMS and fMRI through the use of a neuronavigator that allows the location of brain structures below a certain scalp position. Initially the TMS was characterized and a map of the magnetic field intensity produced by the eight shaped or butterfly coils was determined by different methods. After this step a neuronavigator was devel-oped allowing a superposition of the magnetic field pattern with the fMRI images. The coil position can be varied and the possible stimulated regions can be visualized. This integration of information is expected to improve the TMS accuracy. To verify the efficacy of this method the motor cortex of 10 asymptomatic volunteers were stimulated. The stimulus was monitored with an electromyogram acquired in the hand thumb abductor muscle. The results shown that with the neuronavigation it was possible to stimulate the desired motor region in all the volunteers studied. (AU)