The clinical value of electroencephalogram/magnetic resonance imaging co-registration and three-dimensional reconstruction in the surgical treatment of epileptogenic lesions

With the rapid developments in image processing, new clinical applications of manipulation and three-dimensional (3-D) reconstruction of neuro-imaging are evolving. Combination with other non-invasive techniques aimed at loca lising electric sources in the brain is of particular interest. These techn iques rely on the recording of brain electrical activity and/or the associa ted magnetic fields from multiple areas on the scalp. Data obtained from an electroencephalogram (EEG) or from magnetoencephalography (MEG) can be fus ed in 3-D arrangement with anatomical [magnetic resonance imaging/computeri sed tomography (MRI/CT)] and/or metabolic [positron emission tomography (PE T)] data. Such techniques highlight information on the functional correlate s of anatomical or space-occupying lesions and their role in the localisati on of related symptomatic epilepsy. In the present study we report on metho dological issues and preliminary clinical data on spectral EEG/MRI co-regis tration procedures, offering two examples of children presenting with hemis pheric lesions, one frontal tumour and one temporal arterio-venous malforma tion. The EEG was acquired from 32/64 electrode location. The electrode pos ition and that of four reference points were measured with a dual sensor Po lhemus 3D Isotrak digitiser. Sources of EEG activity were determined in 3-D space with the inverse solution method low resolution electromagnetic tomo graphy (LORETA), providing for each frequency component, the topographic di stribution of active electrical sources. The positions of the reference poi nts were also measured on MRI, and co-registration of EEG and MRI was achie ved using a transformation algorithm. The reconstructed 3-D images of co-re gistered EEG/MRI clearly demonstrate the relationship between the space-occ upying lesion and the epileptic activity. Preliminary results show that in all the patients it was possible to identify with a remarkable accuracy the 3-D topographic relationship between lesion and cortical areas showing loc alised abnormalities on the EEG. The present method could further enhance t he understanding of the effect of resective treatment of structural lesions on brain functioning. The new combined images can be used in combination w ith image-guided surgery equipment to modify effective surgical resection.