Investigation of Blood-Brain-Barrier Breakdown Using Manganese Magnetic Resonance Imaging in Drug-Resistant Epilepsy

Background: \- The blood-brain barrier separates the brain from the rest of the body. Epilepsy is a neurological disease that causes seizures. It can affect this barrier. Researchers think a contrast agent called mangafodipir might be better able to show areas of the brain that epilepsy affects. Objective: \- To see if mangafodipir is well tolerated and safe. To see if magnetic resonance imaging (MRI) using either mangafodipir or gadolinium can show areas of blood-brain barrier breakdown in people with epilepsy. Eligibility: * People ages 18-60 who: * Have epilepsy not controlled by drugs * Prior or concurrent enrollment in 18-N-0066 is required Design: * Participants will be screened with: * Medical history * Physical exam * Blood and urine tests * Participants will have up to 6 visits in 1-3 months. One visit is an inpatient stay lasting 2-10 days. Visits may include: * Video-EEG monitoring for participants with epilepsy * An IV catheter put in place: a needle guides a thin plastic tube into an arm vein. * Getting mangafodipir through the IV. * Getting gadolinium through the IV. * Up to 6 MRI scans over a 10-day period: a magnetic field and radio waves take pictures of the brain. Participants lie on a table that slides into a metal cylinder. They are in the cylinder for 45-90 minutes, lying still for up to 10 minutes at a time. The scanner makes loud knocking sounds. Participants will get earplugs. * A final MRI at least 2 weeks after receiving mangafodipir.