Abstracts

Rationale: Evaluation of language lateralization is critical for epilepsy surgery planning. Functional magnetic resonance imaging (fMRI) is one of the potential tools for this purpose, however, language fMRI has been clinically interpreted by visual inspection. We assessed the usefulness of laterality index (LI), which was derived from surface-based fMRI analysis, for language lateralization in patients with epilepsy.Methods: Eighteen epilepsy patients (male:8, female:10, age:13-50) were studied. Informed consent was obtained from each patient or guardian. All patients showed left language predominance in Wada test. MR images were acquired on a 3T MRI scanner with magnetization-prepared rapid acquisition gradient-echo (MPRAGE; TR=2000ms, TE=2.37ms, flip angle=90, 1-mm isotropic voxels). The functional study consisted of blocked trial runs of a semantic language task. Patients were asked to decide whether each word was abstract or concrete in a visually presented series of words. Images were acquired using an echo planar imaging gradient echo sequence sensitive to blood oxygen level-dependent contrast (TR=200ms, TE=30ms, flip angle=90, 3-mm isotropic voxels). Patients performed three task runs, each of which consisted of three 36-second blocks of word presentation and four 28-second blocks of eye fixation. Task fMRI data were analyzed using FS-FAST software (www.surfer.nmr.mgh.harvard.edu). After preprocessing with motion correction and averaging, hemodynamic responses were calculated using a gamma function. The results were projected on the cortical surface, which was derived by FreeSurfer software (www.surfer.nmr.mgh.harvard.edu). We computed the average hemodynamic responses constrained by positive functional activation in the following areas; parsopercularis, parstriangularis, superior temporal, supramarginal cortices on both hemispheres. The cortical parcellation was obtained by FreeSurfer in each patient. We calculated laterality index by LI = (L-R)/(L+R), where L and R is the sum of activation in all of these cortical areas (LI-total). LI was also obtained for frontal (parsopercularis+parstriangularis; LI-frontal) and temporal (superior temporal+supramarginal; LI-temporal) subset of these cortical areas. For each patient, language predominance was determined based on the LI as follows; ?0.1:left, 0.1>LI>-0.1:bilateral, ?-0.1:right.Results: In LI-total. twelve patients showed the language predominance on the left side consistently with Wada test. Six patients were bilateral. In LI-frontal, fifteen patients showed left predominance, and three were bilateral. In LI-temporal, six patients showed predominance on the left, two on the right, and ten was bilateral. Overall sensitivity was 0.67 for LI-total, and 0.83 for LI-frontal and 0.33 for LI-temporal.Conclusions: Language lateralization determined by LI-total and LI-frontal were consistent with Wada test. FMRI-derived laterality index may be useful for evaluating the language-related function in each cortical area.