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In addition to EEGs and MRIs, other tests may be used to diagnose epilepsy. There are several other neuroimaging scans that, like MRI, construct images of the brain and provide the physician with critical data to help accurately diagnose epilepsy.On this page, we’ll review other neuroimaging tests that can be used to diagnose epilepsy, including:

ABOUT NEUROIMAGING

Neuroimaging tests produce images of the structure or activity of the brain; these tests are done to identify where the seizure begins (origin or focus) and to confirm that there is no other medical condition that could be causing the seizures (for example, stroke).

Neuroimaging may also be done when there is reason to suspect that the cause of the seizures will change over time.

CT SCAN

Computed tomography (CT) scanning (also called “CAT” scan) is a non-invasive technique where low-dose x-rays are used to take cross-sectional images (slices) of the brain.1

CT scans are generally more accessible and quicker to perform than an MRI. The scanning process takes about 15-30 minutes. Because CT scans can be performed quickly, they can be used during emergencies. They may also be used in cases where MRI cannot be performed, for example, when people have metal implants.

CT scans are effective at detecting large tumors, bleeding in the brain, and blood vessel defects. However, the image from a CT scan is not as detailed as the image from an MRI.

During the scan, the person lies flat and still on a bed. The bed slowly moves through a donut-shaped machine while a scanner rotates around the head and emits narrow beams of x-rays. The scanner measures the amount of x-ray absorbed by the body and renders images (slices) through a computer.

The two-dimensional slices can be viewed individually, or they can be stacked together to build a three-dimensional image of the brain.

The scan is an outpatient procedure. It is safe and does not hurt. If you are pregnant (or think that you could be pregnant), you should inform your physician before getting a CT scan. A head CT scan does not directly expose the developing fetus to radiation, however, your physician may recommend a different diagnostic test such as an MRI or ultrasound.3

SPECT SCAN

Single-photon emission computerized tomography (SPECT) is a painless, non-invasive scanning technique used to map the distribution of blood flow in the brain. Before the scan, the patient is injected with a tracing substance which SPECT uses to produce images that show how your organs are working by measuring blood flow.4

In epilepsy patients, it can be used to pinpoint the origin of seizures by identifying the area(s) that have the most blood flow. SPECT testing may be done when it is difficult to find the origin of seizures. In a technique called “ictal SPECT,” the patient will be injected with the SPECT radioisotope during a seizure. These ictal SPECT images will help the doctor pinpoint where the seizures are coming from. This procedure will take place in the epilepsy monitoring unit or the nuclear medicine suite.  You may be asked to stop or reduce the dosage of their antiseizure medication (ASM) in hopes of provoking a seizure.

For the procedure, the patient may be asked to put on a hospital gown and will be asked to remove any jewelry, piercings, or other metallic materials. Before the procedure can begin, the patient will lie on a scanning bed and wait for the radioactive tracer to circulate through the body. This may take 20 minutes or longer.

The patient will lie on the scanning bed as it enters a donut-shaped scanning machine, then lay still while the SPECT machine rotates around them. The scan generally takes about 30 to 45 minutes.

An interictal (between seizures) baseline scan is an inpatient or outpatient procedure. It is safe, and the procedure itself does not hurt. However, insertion of the IV needle and the radioactive tracer may be uncomfortable. The level of radiation used in the SPECT scan is very low and does not pose any harm. The technician may advise you to drink a lot of water or liquids for the next 24 hours to flush the radioactive tracer substance from your body.

Because a SPECT scan uses a radioactive tracer, it is not commonly used in pregnancy. Inform your physician if you are pregnant, think that you may be pregnant, or are nursing.

PET SCAN

Positron emission tomography (PET) scans are used to give your physician a better idea of how your brain is using glucose. Like the SPECT scan, PET start with a small amount of a radioactive substance injected into the arm or through an IV and spreads throughout the patient’s body. The machine scans the body and detects the photons (subatomic particles) being emitted by the injected radioactive tracer in the brain or whatever part of the body that is being scanned.

For epilepsy, it can help your physician identify the part of your brain that is causing the seizure activity. PET scans may be used to find the seizure origin in case of focal (partial) seizures, for evaluation before epilepsy surgery, and also to see how the brain utilizes glucose between seizures (interictal period). Neither CT scans nor MRI can provide this type of information.

For the procedure, the patient may be asked to put on a hospital gown and will be asked to remove any jewelry, piercings, or other metallic materials. After the IV has been inserted and the tracing substance has circulated through the body, the patient will lie on the scanning bed as it enters a donut-shaped scanning machine, then lie still while the PET scanner detects where in the body the radioactive material has reached. That information is sent to a computer that creates detailed 3D images.

The scan is an outpatient procedure. It is safe and the procedure itself does not hurt. However, insertion of the IV needle and the radioactive tracer may be uncomfortable. The level of radiation used in the PET scan is very low and does not pose any harm. The technician may advise you to drink a lot of water or liquids for the next 24 hours to flush the radioactive tracer substance from your body.

Because a PET scan uses a radioactive tracer, it is not commonly used in pregnancy. Inform your physician if you are pregnant, think that you may be pregnant, or are nursing.4

MEG SCAN

Just like an EEG detects electrical signals in the brain, magnetoencephalography (MEG) detects magnetic signals that arise in the brain. It is the newest, most advanced non-invasive technique used to pinpoint the source of abnormal brain and seizure activity.5

It produces very high-resolution images because it has a high number of sensors and the signals are not impacted by the skull or scalp. Many times, MEG is combined with MRI to provide an idea of the structure of the brain along with its magnetic signals.6

MEG can be used to accurately pinpoint where the seizures are coming from in a way that is more accurate than other techniques. MEG may also be used to plan for epilepsy surgery and may be used to accurately determine the location of a brain tumor.

It can also be used to evaluate how the brain responds to stimuli so that your physician or a neurosurgeon can map critical areas of the brain for language, vision, motor skills, and other functions.

Because magnetic waves are involved in MEG, the patient may be asked to put on a hospital gown and will need to remove any jewelry, piercings, dentures, or other metallic materials because they may affect the reading. You may not be able to undergo a MEG scan if you have metal in your body and should discuss it with your physician. That includes vagal nerve stimulators (VNS), pacemakers, insulin pumps, cochlear implants, body piercings, metal plates, surgical clips, pins, staples, wire mesh, screws, metal fragments, bullets, shrapnel, or tattoos (some tattoo inks contain metal).

The patient will lie on a bed or sit in a chair, and the technician will measure the shape of the head and affix flat coils on the head. These coils are connected to a recording machine, which produces an image of the magnetic signals in the brain. The patient’s head will then be positioned inside of a helmet that resembles a beauty shop hairdryer. The patient will need to be the only person in the room, but the technician will be able to communicate with the patient through a microphone. The machine does not make any noise. The scan generally lasts from 1 to 4 hours, and you will be asked to be very still and to limit eye movements. You may be able to sleep for part of the scan, and/or you may be asked to perform some tasks such as pushing a button or talking.

The scan is an outpatient procedure. MEG is safe and does not hurt. MEG does not use radiation, so it is safe for pregnant individuals, unlike CT, PET, and SPECT. Because it is a relatively new technology, it is not available at all centers.

THINGS TO TALK ABOUT WITH YOUR DOCTOR

Below are a few points you may want to discuss with your doctor before getting any of the tests described above:

  • Confirm the drugs and supplements you are taking and at what time of the day, and if you should stop taking any of them before the procedure
  • Discuss any metallic materials that you may have including vagal nerve stimulators, pacemakers, insulin pumps, cochlear implants, body piercings, metal plates, surgical clips, pins, staples, wire mesh, screws, metal fragments, bullets, shrapnel, or tattoos
  • Inform your physician if you are pregnant, think that you may be pregnant, or are nursing
  • Inform your physician if you are claustrophobic or unable to stay still inside a scanner; your physician may be able to prescribe a medication to help you relax during the procedure

References:

  1. Raji CA, Tarzwell R, Pavel D, Schneider H, Uszler M, Thornton J, et al. Clinical utility of SPECT neuroimaging in the diagnosis and treatment of traumatic brain injury: a systematic review PLoS One. 2014;9:e91088.
  2. https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  3. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/10/guidelines-for-diagnostic-imaging-during-pregnancy-and-lactation
  4. https://www.mayoclinic.org/tests-procedures/spect-scan/about/pac-20384925
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5888841/#:~:text=Positron%20emission%20tomography%20scanning%20is,tomography%2Fcomputed%20tomography%20in%20pregnancy
  6. https://www.radiologyinfo.org/en/info/meg#:~:text=Magnetoencephalography%20(MEG)%20is%20a%20non,the%20source%20of%20epileptic%20seizures
  7. https://www.henryford.com/services/epilepsy/diagnosis/meg-scan

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