The major hypothesis explaining drug resistance is overexpression of p-glycoprotein at the target lesion. Based on several studies, p-glycoprotein (P-gp) has an important role in neurologic diseases, especially in drug resistant epilepsy. But there is no surrogate marker that can quantify the expression of P-gp because of the difficulty in measuring substances in the neurologic system and the lack of clinical trials. Here, the investigators use a novel non-invasive [11C] -verapamil Brain PET and SPAM analytic method as a surrogate marker for quantifying the expression of p-glycoprotein.