Integration of MRI and EEG
Measured electroencephalograph (EEG) signal and magnetic resonance (MR) images can be integrated by applying 3D computer graphics. Such technique increases the spatial information of EEG, and in addition, enables efficient visualization of consecutive EEG samples as an animation. For this purpose several algorithms and a software was developed.
The 3DEEG  software was developed to PC/Windows95 environment using C++ language. The software is capable in calculating automatically electrode locations for 10-20 (21 channels) and 10-10 (64 channels) electrode systems. However, the user must first select nasion, inion, and pre-auricular nodes from the MRI set. That can be carried out using the user interface presented in Fig 1.
Figure 1: The user selects nasion, inion, and pre-auricular nodes from the MRI set.
The 3DEEG software generates a 3D surface for a MRI set by applying the method of Ray Casting. Thereafter a polygon mesh is generated between the electrodes and possible "virtual electrodes". The 3D surface and the polygon mesh are matched and displayed simultaneously. Measured EEG potentials are interpolated between the electrodes and drawn using partially transparent colors. The software enables several different projection planes. The user interface is presented in Fig 2.
Figure 2: The user interface of the 3DEEG software (10-20 electrode system)
The measured EEG signal is possible to present as animation. On a 200 MHz Pentium based computer the software is capable of updating the map five times per second.
The software has been applied in epileptic studies; measured and simulated signals have been compared as a brain map. Such technique enables efficient and easy method for comparing different signals.
 Heinonen T, Häkkinen V: Implementation of 3D Brain Mapping, Submitted to Computers and Biomedical Research, 1997.
For further information, please contact:
Tomi Heinonen, Email: email@example.com, fax: +358 3 247 4013, tel: +358 40 547 1451