This study will evaluate a type of Magnetic Resonance Imaging (MRI) sequence called arterial spin labeling (ASL). The investigators hope that ASL can better localize areas of the brain (lesions) that cause epilepsy. This type of MRI does not require contrast, does not use any radiation, and adds on 4 minutes to the routine MRI that is done for patients with epilepsy.

The study hypothesis is that in patients with refractory epilepsy, Arterial Spin Labeling (ASL) MRI will show areas of abnormality in the brain to the same degree as single-photon emission computerized tomography (SPECT) and positron emission tomography (PET) studies.

Currently, in presurgical evaluation of epilepsy patients, PET and SPECT studies are utilized to evaluate metabolic and perfusion abnormalities respectively to localize seizure onset. This is especially true in "MRI negative" patients, whose lesion is not visible on standard MRI techniques. PET and SPECT studies have numerous disadvantages, including radiation exposure, injection of contrast or isotopes, cost, and are often difficult to access for many patients.

Arterial spin labeling (ASL) MRI sequences show perfusion related abnormalities without using contrast, in a relatively short amount of time, and can be done during a normal MRI for evaluation of epilepsy. This is of interest because if there is a good correlation, ASL MRI sequences could be used in addition, or in place of, these other studies that require injection of isotopes and radiation from CT scans.

ASL sequences have been shown to localize certain epileptogenic abnormalities such as tubers in tuberous sclerosis. A previous study demonstrated ASL changes inter- and post-ictally in one patient without other MRI changes. This is a promising technique that has not been fully evaluated as of yet. Of note, all studies done in this area in regards to epilepsy have been retrospective, small studies. The investigators plan to perform a study that is prospective, with a comparatively large sample of patients.

Study Design: Consultants in the epilepsy clinic will identify potential subjects on the patients' initial evaluation. Just after the consultation is finished, in the epilepsy clinic, the study will be described to the patient along with risks and benefits, and informed consent will be obtained by one of the researchers or research personnel in the clinic. If the patient agrees with the study, the MRI department will be notified of the patient's participation. At that time, the patient's already scheduled MRI will have the addition of ASL sequences. This will add approximately 4 minutes to the MRI. The patient will then have other imaging investigations as deemed necessary by the treating consultant. This may include PET and SPECT. If the patient is admitted to the EMU, ictal and interictal SPECT are likely to be done. After the patient has had the full evaluation, we will compare the ASL MRI sequences to the basic MRI, and PET and SPECT if performed.

We will also use software already developed to determine the quantitative blood flow to the abnormalities found on the ASL sequences.

Inclusion Criteria:

• Medically refractory partial epilepsy.
• Over the age of 18 years.
• Scheduled to have routine epilepsy-protocol MRI after initial evaluation in neurology clinic at Mayo Clinic, Rochester.
• Anticipated to undergo epilepsy monitoring unit (EMU) monitoring.

Exclusion Criteria:

• Patients with a generalized epilepsy.
• Under the age of 18 years.
• Unable to undergo MRI imaging of the brain.

Small sample size.