Neuroimaging - MRI, CT, SPECT and PET scans

Neuroimaging, or brain scanning, is predominantly performed to look at the structure of the brain. The techniques outlined below may further assist in the diagnosis of epilepsy. Pictures are taken of the brain that may show changes in brain tissue structure and cell function. Changes may indicate for example:

• the presence of scar tissue from an injury
• a lesion or tumour
• degeneration or shrinking of brain tissue
• changes in blood flow in the brain
• changes to metabolism of substances such as glucose

Common tests include:

MRI Scanning
MRI or Magnetic Resonance Imaging produces clear and detailed images of the brain without the use of x-rays. It uses strong magnetic field and radio frequency waves that produce and measure energy changes in the brain and then generates images. Technology has advanced and the MRI can now produce three-dimensional images of the brain on a computer. Two-dimensional images can be printed onto film.

The person is lies on a table and the table moves inside the scanner, which is like a tunnel. During the scan, the machine makes a loud thumping noise. This can be distressing for those who dislike confined spaces, a mirror at the person's head provides a view of the room and the operator, while a call button and an intercom allows contact. Earplugs should also be available.

The procedure lasts from 30-45 minutes.

Because of the strong magnetic field people with pacemakers, cerebral aneurysm clips and any other metal surgical implants will not be able to have a MRI scan.

It is important to remove jewellery, hairclips, hearing aids, credit cards, coins, keys, even makeup and hair gels which could interfere with the scan.

The MRI scan is not known to have any harmful effects.

It is advisable to tell staff prior to the scan if you suffer from claustrophobia (fear of being in a confined space).

Again, complete stillness is required during this test and young children may require sedation or a light, general anaesthetic. The entire procedure takes from 30-60 minutes.

For more information on MRI scans.....Click here.

CT Scanning
Computed Tomography (CT) is a procedure that uses x-rays to take pictures of the brain, displayed as cross-sectional images or slices.

The person lies on a table, and only the head moves into the CT scanner. Pictures are taken at many angles to generate the brain images. Sometimes to enhance the different structures and give more contrast, a dye is injected into a vein of the arm or hand. On occasion a person is allergic to the dye: this may cause a skin rash and, rarely, difficulty with breathing.

The entire procedure takes from 30-45 minutes. The test is painless except for the discomfort of the injection if this is required.

As complete stillness is required during the test, young children may require sedation or a light, general anaesthetic.

For more information on CT scans....Click here.

SPECT Scanning
SPECT also uses a computer to generate pictures of the bloodflow within the brain. It is often performed twice, in a seizure free period (interictal) and immediately after a seizure (ictally) – although the radioactive substance (Cerotec) is injected during the seizure. Both scans are compared to identify changes in blood flow in the brain. Blood flow in the area triggering seizures can be reduced in-between seizures and temporarily increased during seizures.

A radioactive substance is injected into a vein and is carried to the brain via the bloodstream. The person lays on a table and the head moves inside the scanner. The scan produces a picture of the brain highlighting blood flow.

Scans usually take 30 minutes and are mostly performed in hospital as part of EEG/Video monitoring. This test is often used as part of the workup for surgery for epilepsy.

PET Scanning
PET scanning measures metabolic activity, looking at function rather than structure of the brain. It produces a three dimensional image of the brain. In a person with epilepsy, the region of the brain where the seizures originate from often has decreased metabolism, the cells are not as active in-between seizures (unless a seizure occurs during the uptake of the substance which will increase activity in the region, thus increases metabolism).

The person will be asked to fast for the test because it is glucose metabolism that is being measured. With someone with epilepsy, often a video telemetry EEG is performed simultaneously, so it is necessary to arrive early for application of the EEG electrodes.

The radioactive substance is injected and the person will be given ear plugs and eye patches to reduce any outside stimulation that can influence the scan. This is a 30-minute period and remaining awake at this time is also important. Blood tests will also be taken during this period. After this, the scan commences, a mask will be put over your face to assure no movement, and your head moves into the scanner.

It can last from 30-45 minutes.

PET is may be done to help establish if someone is suitable for epilepsy surgery.

PET scans

For more information on PET and SPECT scanning....Click here.

For more details about neuroimaging and epilepsy....Click here.

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