The Johns Hopkins Epilepsy Center

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Imaging studies are utilized to evaluate the structure of the brain or to evaluate its function.

At present, structure is usually assessed with Magnetic Resonance Imaging (MRI), although Computerized Tomographic (CAT) Scans are also used. When there is a structural abnormality in the brain, that area, or an area near it, may be causing the patient's seizures. Assessments of various areas of the brain, particularly the hippocampus, have proven useful in localizing and lateralizing areas of epileptogenesis. Magnetic resonance techniques are now beginning to be used to assess brain function as well, using methods such as Functional MRI and magnetic resonance spectroscopy (MRS). In addition, radiotracer-based methods such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) can be used to look for areas of the brain with altered metabolism, blood flow, or neurotransmitter function. The idea is that these areas of altered activity are more likely to be areas producing seizures in a given patient.

MAGNETIC RESONANCE IMAGING (MRI)

Magnetic Resonance Imaging (MRI) provides physicians a means by which a physician can see a patient's internal body structures without using x-rays. This technology enables physicians to detect developing diseases or abnormalities earlier than ever before. Basically, MRI involves a powerful but harmless magnetic field and radiowaves like the kind that transmit FM music. The combination of radiowaves and magnetic field produces very clear images of body structures such as the brain, the spine, and other vital organs. By looking for abnormalities in structure, the epilepsy team can determine whether there may be seizure producing areas in or adjacent to the regions of structural change. In addition, new techniques are being developed such as magnetic resonance spectroscopy (MRS) and functional magnetic resonance imaging (fMRI) which can evaluate brain function.

What Kinds of Machines Are Used to Perform MRI?
The patient's scan will be performed in a room containing "the magnet." The MRI unit looks like a large box with an open-ended tunnel running through the middle. Many different kinds are in use, but they all work in the same way. The patient will be asked to lie on a comfortable, padded table that is gently moved into the opening of the magnet where the scanning is performed.

Sometimes a "coil," which is really just a special radio receiver, will be placed around the body part being scanned (the patient's head, or knee, or stomach, etc.). The data from the scan is fed into computers which compose very clear pictures that the physician will use to make a diagnosis.

What Happens the Day of The Exam?
The patient should allow about two hours for the MRI exam, although most scans take an hour or less.

Unless the patient's doctor indicates otherwise, the patient can eat normally the day of the exam. The patient should not wear any makeup, since some brands contain metallic components. On arrival at the MRI center, the patient will be asked to put on a gown and to remove all personal possessions such as jewelry, wallet, car keys or metallic items such as dentures, pins, etc.

It's very important not to take anything that could be affected by a magnet into the examining room. For example, the information on credit cards could be erased if the patient has them in a pocket during the exam!

While the vast majority of people can undergo an MRI exam with no problems, some cannot. The radiologist or the staff at the MRI center will probably ask the patient questions like the following:

Does the patient weigh more than 300 pounds?
Can the patient lie flat for an extended period of time?
Does the patient suffer from claustrophobia?
Is the patient pregnant?

Since the MRI Scan involves the use of a powerful magnet, the patient will also be asked the following kinds of questions:

Does the patient have any implanted devices such as a cardiac pacemaker, a cerebral aneurysm clip, a neurostimulator, or a hearing aid?
Does the patient have any metal shrapnel in the body or any metal fragments in the eyes?

The patient should remember that the questioning process is a two-way street. After providing all of the necessary information, the patient should feel free to air any concerns about the upcoming examination. Radiologists and their technologists expect questions and part of their job is answering them.

What Happens During the Actual Exam?
The patient will be escorted into the room containing the "magnet" by a technologist and will be asked to lie down on the padded table. The technologist will position the patient inside the magnet so that the appropriate part of the patient's body is ready to be scanned. During the exam, the patient will be able to talk with the people conducting the exam by means of an intercom and they will be able to watch the patient through a glass window.

The patient may hear very loud clanking and thumping sounds which the machine makes as the technologists adjust the radio frequencies and other controls. These sounds are completely normal, but since they can be loud, some centers supply ear plugs for patients.

Sometimes a radiologist, nurse, or technologist may come into the scanning room to inject an enhancement agent to help the radiologist interpretthe pictures taken during the exam.

Side Effects
Since MRI uses harmless radiowaves and magnetization instead of x-rays, it is considered to be safer than other radiologic techniques that do use x-rays. There are no known side effects.

POSITRON EMISSION TOMOGRAPHY (PET Scan)

With a PET Scan, changes in brain metabolism and chemistry can be observed. Although a PET Scan can help to evaluate many medical conditions, it can be of particular value in evaluating patients with epilepsy.

The PET Scan Procedure
To begin the procedure, a plastic mask is fitted onto the patient's face. This aids in positioning the patient's head in the scanner. Baseline x-rays often are taken, either by CT scan or MRI. These studies, performed in another location, are done using equipment other than the PET scanner. The PET scan begins when a small amount of radioactive material is injected into a vein in the arm and, at the same time, a blood sample is taken from the other arm. For some types of PET scans, the patient's eyes will be covered and the patient's ears plugged for thirty minutes after the injection to minimize sensory stimulation.

The PET scan generally takes less than two hours, during which time the patient must lie quietly with the plastic mask in place. If the patient has had a CT scan, the experience of being "inside" the PET scan is similar.

Risks and Discomforts
There are no serious complications or discomforts with PET scanning. The patient may experience minor discomfort with the placement of the intravenous needle. Some patients find it uncomfortable to lie still in the PET scanning bed for the length of time required for the study.

As with all radioactive materials including x-rays, there is a slight risk associated with the radioactive material that is injected. The dose of radiation received in a PET scan is slightly more than that received in a chest x-ray, but less than that received from most digestive studies. Women who are pregnant, or suspect that they are pregnant, should not have a PET scan.