S G Andino | PubMed Health

PubMed2001

Volumetric measurements of subcortical nuclei in patients with temporal lobe epilepsy.

OBJECTIVE: To determine the volumes of subcortical nuclei in patients with chronic epilepsy. BACKGROUND: Animal and human data suggest a crucial role for subcortical structures in the modulation of seizure activity, mostly as seizure-suppressing relays. Although cortical epileptogenic foci can vary in localization and extent, it nevertheless appears that these structures subsequently influence seizure propagation in a universal fashion. There is, however, little knowledge about the size of implicated subcortical structures in patients with epilepsy. METHOD: Using high-resolution MRI, the volumes of selected subcortical nuclei, such as the thalamus, caudate nucleus, putamen, and pallidum, were measured in both hemispheres of 27 patients with temporal lobe epilepsy. Fourteen healthy volunteers served as controls. Statistical analysis was done for both normalized volumes (by total brain volume) and unnormalized volumes. RESULTS: Overall, the patient group had smaller thalamic and striatal volumes in both hemispheres, mostly ipsilateral to the epileptic focus. No significant correlations were noted between volume measurements and age, age at onset, duration of epilepsy, or total seizure frequency, including frequency of generalized seizures. The putamen and thalamus seemed to be affected predominantly in patients with a history of febrile convulsions, whereas patients without febrile convulsions had smaller caudate nuclei bilaterally. CONCLUSIONS: Volumetric measurements of subcortical nuclei reveal atrophy of distinct subcortical nuclei in the patient group, predominantly ipsilateral to the focus. This finding probably reflects persistent abnormalities and not secondary change. In addition, the structural differences between patients with and patients without previous febrile convulsions suggest that these conditions may have different causes.

Adult↗

PubMed2000

Electromagnetic inverse solutions in anatomically constrained spherical head models.

Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI, and electromagnetic techniques such as EEG/ERP and MEG. In order to fusion these images with anatomical information, co-registration with volumetric MRI is needed. While such co-registration techniques are well established for hemodynamic images, additional steps are needed for electromagnetic recordings, because the activity is only recorded on the scalp surface and inverse solutions based on specific head models have to be used to estimate the 3-dimensional current distribution. To date most of the experimental and clinical studies use multi-shell concentric sphere models of the head, solve the inverse problem on this simplistic model, and then co-register the solution with the MRI using homogeneous transform operations. Contrary to this standard method, we here propose to map the MRI to the spherical system by defining transformation operations that transform the MRI to a best-fitting sphere. Once done so, the solution points are defined in the cerebral tissue of this deformed MRI and the lead field for the distributed linear inverse solutions is calculated for this solution space. The method, that we call SMAC (Spherical Model with Anatomical Constrains) is tested with simulations, as well as with the following real data: 1) estimation of the sources of visual evoked potentials to unilateral stimulation from data averaged over subjects, and 2) localization of interictal discharges of two epileptic patients, one with a temporal, the other with an occipital focus, both confirmed by seizure freedom after resection of the epileptogenic region.

Brain↗