Displaying electroencephalographic dipole sources on magnetic resonance images

A simple, inexpensive method of displaying electroencephalographic (EEG) dipole sources on magnetic resonance images (MRIs) is presented. It consists of measuring the head according to the 10-20 system but instead of placing electrodes, benzonatate capsules (Tessalon Perles) (100 mg) are affixed to the patient's scalp. MRI is obtained with the capsules in place. In addition to the routine images, thin-section (1.0-1.3-mm) scans in a three-dimensional volume are obtained and the coordinates for each electrode position ascertained. The capsules are then replaced by electrodes and a waking and sleep recording is performed with a digital EEG instrument. Phenomena of interest are then averaged and interfaced with a source analysis program. The three-dimensional electrode coordinates are placed in a file and used to establish the electrode cloud on the basis of which source analysis proceeds. The three-dimensional source locations are then superimposed on the MRIs. The method is useful in the workup of epilepsy patients, by relating focal epileptogenic activity to definable lesions, and it also allows more precise localization of normal EEG phenomena.