| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所 === 87 === The spatial-temporal characteristics of epilepogenic focus activity can be recorded from scalp electroencephalograph (EEG). The three-dimensional equivalent dipole source within the brain can be localized using an inverse solution from the EEG. In addition, the magnetic resonance image (MRI) is usually used to acquire the brain structural information. The aim of this study is to map the coordinate of EEG electrodes to the MRI coordinate.
The patients with their EEG showing interictal spikes activity at seizure onsets were selected for this study. The EEGs were recorded from 27 electrodes fixed on a Quik-CapR placed as the International 10-20 montage. The measurement of EEG electrode position was using a 3-D magnetic digitizer, and used to determinate the EEG coordinate. For directly visualizing the electrode positions on the 3-D MR images, the MR images were acquired instantly while the EEG electrode markers were attached to the scalp. Because those electrodes were fixed on immobile position, the relative location was stationary during both EEG and MRI recordings. Image segmentation of the MRI was performed to extract structures of the head surface, the brain surface and the electrode markers. The point-mapping approach for registration between EEG electrodes and MRI coordinates was adopted in this research. An iterative process is performed to determine the proper transformation to match the electrode points in EEG and those in MRI. Because of the distortion in electrode positions caused by the lied down during image taking of MRI, the exact match between two coordinates may not exist. We developed a simple approach for initial estimation of transformation matrix, which can constrain the search space and improve the estimation accuracy.
From the varied simulation cases, the proposed registration technique performed well disregarding the sequences of rotation and translation s. In addition, the initial estimation can provide transformation very close to the exact solution under the condition that the position distortion is small. For a high distortion case, convergence can be reached with increased numbers of iteration. Toward the integration of MRI data and the dipole localization of the epilepsy focus is the future trend of similar research.
|
|---|
