Magnetic Source Imaging (MSI) / Magnetoencephalography (MEG)

What is MEG?

  • MEG stands for magnetoencephalography.
  • It is noninvasive and works like a very sensitive microphone that records magnetic fields emitted by brain cells (neurons) instead of sound.
  • The MEG scanner collects information from 275 sensors simultaneously every millisecond.
  • The MEG scanner is silent and fits on your head like a helmet.

How is MEG different from EEG (electroencephalography)?

  • MEG senses the magnetic fields produced by neurons in your brain while EEG senses electrical signals from the brain.
  • Sometimes EEG is collected at the same time as MEG to gather reference information about where the brain activity is coming from.

How is MEG different from brain MRI (magnetic resonance imaging)?

​MRI collects structural information and creates images of the brain while MEG collects magnetic activity from neurons, visualized as brain waves.

  • The MRI machine uses a large magnet to help create images; in MEG there is no magnet.
  • The MEG is used with MRI in magnetic source imaging (see the next section).

MEG Referral Instructions

If you are referring a patient for a magnetoencephalogram, please follow the instructions below to start the referral process.

  1. Fill out the MEG Referral Cover Sheet (pdf)
  2. Have the following medical information ready to be sent to us:
    • Patient’s Demographic and Insurance Information
    • Patient Insurance Card
    • Authorization for Magnetoencephalogram if required
    • Recent MRI Brain Reports
    • Recent Video EEG Monitoring Reports (if available)
    • Recent PET and/or CT Scan Reports (if available)
  3. Include MEG Referral Cover Sheet (pdf) and all pertinent medical information listed in step 2 to be sent to following email: [email protected]
  4. If your patient requires pre-authorization for magnetoencephalography, please pick which procedure your patient will receive and use the following CPT codes to initiate pre-authorization:
    MEG/MSI Standard Presurgical Epilepsy Study
    CPT 95965, 95812, 95966, 95967
  5. If your patient’s insurance agency requires a Tax Number and/or NPI for billing purposes, please provide the following:

    • UCSF Biomagnetic Imaging Lab Tax ID #: 94-3281657
    • UCSF Biomagnetic Imaging Lab NPI#: 1639278369
  6. We also require referring providers to send MRI brain images (DICOM files) or schedule a new MRI brain scan at UCSF in addition to the MEG referral.  To be used, a prior MRI brain image must meet the following guidelines:

    • High-resolution 3D MPRAGE or SPGR T1-weighted scan, or 3D FSE T2-weighted scan.
    • NOT a multi-angle or oblique scan.
    • Images should have black space around the whole head with coverage of fiducial landmarks (inion, bilateral pre-auricular points & tragi, etc.)
    • Scan must be within the prior two years for patients 22 and older, within the prior year for patients ages 12-21, and within the prior six months for patients under 12. If a patient has had brain surgery since their most recent scan, they will also need an updated scan prior to MEG.
    Please send high-resolution 3D images through FedEx or UPS express, or electronically if possible.

    For FedEx please send a CD copy to:

    UCSF Biomagnetic Imaging Lab
    513 Parnassus Ave, Room S-362
    San Francisco, CA 94143-0628

    If electronic transfer is possible, please transfer the patient’s MRI Brain Images to: 

    UCSF Radiology Referral Box

To schedule an MRI at UCSF during the same visit, please refer to scheduling instructions here and fax the Radiology Order Form to 415-353-7299, indicating "3T Epilepsy protocol" and "urgent order." MEG date should be finalized first.

After we have received all required materials, we will contact the patient directly for MEG scheduling. If you have any questions, please feel free to contact us at [email protected] or call us at (415) 476-6888. You can also fax us at (415) 502-4302. Providers may contact our clinical director, Dr. Heidi Kirsch at [email protected].

​What is MSI?

MSI stands for magnetic source imaging.

  • MSI combines MEG and MRI results to create functional maps of brain activity. These maps can show where areas of normal and abnormal activity are located.
  • Clinically, MSI can provide increased localization of spike activity in patients with seizures. MSI can look at activity deeper in the brain than EEG alone.
  • Clinically, MSI can also map areas of function (language, hearing, touch, movement, etc.) in presurgical patients.
  • Both spike localization and functional mapping information are typically used prior to surgery for planning purposes and also during surgery using surgical navigation systems.

What should I know before coming to my appointment?

Because the test is very sensitive to metal, we ask that you please let us know immediately if any of the following conditions apply to you. A technologist will then let you know whether you can have the exam or not.

  • Have an implanted electrical device such as a pacemaker, vagus nerve stimulator (VNS), or deep brain stimulator (DBS).
  • Have an implanted metal device or prosthesis such as a metal plate, aneurysm clip, rod, pin, screw, etc.
  • Have nonremovable dental work such as braces, permanent retainer, bridge, etc.

How to prepare for your appointment

  • Wear clothes free of metal zippers or snaps above the waist (pants with zippers are ok).
  • Avoid make-up, especially eye make-up (make-up can contain metallic ingredients that can affect the scan).
  • Please wear your hair down and without hair products.
  • Please let us know if you need interpreting services, this can be arranged for you.
  • Please bring a list of your current medications

What can I expect before my MSI exam?

​There is little preparation for an MSI exam. You can eat normally and take your daily medications as you normally would, unless instructed otherwise by your physician.

  • You will be asked to remove all metallic items from your body such as belts, eyeglasses, cell phones, credit cards, keys, etc.
  • If you have metal on your clothing, you will be asked to change into a hospital gown.
  • A technologist will verify your identification and record a brief interim history including your current symptoms.
  • If you are having an EEG exam done at the same time, we will place electrodes on your scalp with a little electrode paste prior to your exam.

What can I expect during my MSI exam?

  • You will be asked to lie on a bed and the technologist will place you in the scanner. The scanner fits on your head like a helmet and is open.
  • You will be asked to remain still while the scan is running. Usually, each scan lasts about 4 to 10 minutes, and in between the scans you will be able stretch and readjust your position. Most appointments involve multiple scans and last between 1-2 hours but can be longer or shorter depending on what your doctor has ordered.
  • At times you will be asked to relax with your eyes closed and other times you may be asked to actively participate in the scan such as listening to tones or responding to pictures.
  • There is a two-way intercom and video monitoring system in the room so that the technologist will be able to monitor and communicate with you at all times.

What can I expect after my MSI exam?

  • The technologist will remove the electrodes if you had an EEG performed and escort you out of the room.
  • The clinical team will analyze and review your scan results and send the results to your health care professionals.

​Will any part of the testing hurt?

The scan is completely noninvasive and should not hurt at all.

Does the scanner use radiation?

No, the scanner does not emit radiation or magnetic fields. It is like a giant microphone that detects brain activity.

Will you inject anything into me?

No, we do not use any intravenous (IV) equipment, contrast material, or sedation.

Who can I ask any additional questions I may have about my appointment?

Please feel free to call the Biomagnetic Imaging Lab at (415) 476-6888 if you have any additional questions or concerns.