Abstracts

Rationale: Task-based functional MRI (fMRI) is commonly used for language lateralization in presurgical evaluation of epilepsy. Resting-state fMRI also demonstrates laterality by calculating intrinsic activity. We assessed concordance of laterality obtained from tasked-based, resting-state fMRIs and intracarotid amobarbital procedure (IAP) in epileptic patients. Methods: Fifteen patients (male:7, female:10, age:15-46) were studied. MPRAGE sequences were acquired on a 3T scanner (TR=2000ms, TE=2.37ms, flip angle=90, 1-mm isotropic voxels). Resting-state fMRI was obtained using an echo-planar imaging (EPI) gradient-echo pulse sequence (TR=3000ms, TE=30ms, flip angle=85, 3-mm isotropic voxels, nframes=160). Patients looked at a white screen for 8 minutes run. The relative correlation strengths between seed and target region pairs were measured, deploying 200 regions in each hemisphere. For each region, laterality index (LI) was defined by [(LL-RL)-(RR-LR)]/[|LL|+|LR|+|RR|+|RL|], where LL/LR/RR/RL are the correlation strength between the left/right seed and the left/right target. We performed factor analysis by using principal axis factoring and obtained LIs in four independent subregions. The fourth factor includes frontal and temporal language areas in the distributed anatomy, and is highly correlated with language laterality represented by task-based fMRI in healthy population (Liu et al., 2009). We used the fourth factor LI for further analysis. The task-based study consisted of blocked trial runs of a semantic language task. Patients decided whether each word was "abstract" or "concrete" in visually presented words. Patients performed three runs, each of which consisted of three 36-second blocks of word presentation and four 28-second blocks of eye fixation. EPI sequences were acquired (TR=200ms, TE=30ms, flip angle=90, 3-mm isotropic voxels) for each run. The data were analyzed using FS-FAST. We computed maximum positive activation in parsopercularis, parstriangularis, superior/middle temporal, supramarginal and inferior parietal cortices on both hemispheres. LI was obtained by (L-R)/(L+R), where L and R is the sum of the maximum activation in each area. For both methods, language laterality was determined based on the LI as follows; ≥0.1:left, 0.1>LI>-0.1:bilateral, ≤-0.1:right. Results: In IAP, 13 patients showed the language laterality on the left side. One patient was right-sided and the other one was bilateral. In task-based fMRI, 12, one and two were left-, right-sided and bilateral. In resting-state fMRI, six, three and six were left-, right-sided and bilateral. We estimated the concordance of task-based and resting-state fMRI with IAP regarding the laterality in the epileptogenic hemisphere. Positive and negative predictive values were 89% and 100%, 70% and 80% for task-based and resting-state fMRI, respectively. Conclusions: Resting-state fMRI showed more bilateral representation of laterality than task-based fMRI. Intrinsic functional connectivity of the language network may be altered in epileptic patients due to plasticity in the overall network induced by epilepsy.