The Neuromag® is a state-of-the-art neuromagnetic recording system capable of non-invasively recording magnetic fields produced by neuronal activity occurring within the brain. This observed data is called the magnetoencephalogram (MEG) and is analogous to the electroencephalogram (EEG) but represents the magnetic fields produced by ion flow associated with neuronal activity rather than the electric potentials measured in the EEG.

Neuromag MEG unit.

This system is designed to:

1. enhance pre-surgical planning by non-invasively localizing eloquent areas within the brain,
2. enhance localization of seizure foci by mapping sources of spiking activity, and
3. assess distributions of brain activity related to cognitive function.

Magnetic fields are found whenever there is charge flow (current), whether in a wire or neuronal tissue. The orientation of the magnetic field is governed by the right hand rule which essentially constrains the MEG system to sensing magnetic fields produced by groups of neurons located tangentially to the cortical surface.

The magnetic field passes unaffected through brain tissues and the skull, so it can be recorded outside the head by the Neuromag system.

The Neuromag system installed at UPMC -- Manufactured by Elekta Instruments in collaboration with Helsinki Technical University -- contains 306 superconducting sensors mounted within a low temperature container (called a dewar) shaped to allow the head to be placed adjacent to the sensors. Thus 306 separate recordings of magnetic activity may be simultaneously made. The spatial distributions of the magnetic fields sensed by n these sensors are then computationally analyzed to localize the sources of the activity within the brain.

The most frequently used computational model is that of a current dipole. The computed locations of the sources are than superimposed on anatomical images, such as MRIs or CTs, to provide information about the relationship between structure and function in the brain. Not all studies require the merging of anatomical and MEG data to be useful. For example, predictive information about recovery from brain concussions may be obtained without merging the data.

MEG Laboratory

With MEG, signals are extremely small, on the order of 10-14 Tesla, which are several orders of magnitude smaller than other signals in the environment. These stray magnetic signals can obscure the brain signals even with signal processing. Thus, the Neuromag system is installed in a specialized magnetically shielded room (MSR) to eliminate the magnetic interference.

The electronics system necessary for recording the magnetic activity from a patient are located outside the MSR. These systems include the MEG amplification and data-acquisition system, a 128 channel EEG recording system, and electrical, visual and auditory stimulation system controllers.

Also located outside the MSR is the computer console used to perform a study and the various computer workstations for analyzing the data.

Housed in the MSR is the MEG sensor, which is comprised of an array of detector coils cooled with liquid helium (-269° C) and contained within an insulating dewar . All devices and materials within the dewar must be non-magnetic and must not produce magnetic fields that can interfere with the recordings.

The interior of the MSR is lit and has a quiet, soothing atmosphere. During an MEG study, the patient is comfortably positioned within the MSR on a patient support system, in either a seated or supine position. While in the MSR, the patient is monitored by closed circuit monitor and intercom at all times.
For most clinical studies, the support system is configured as a bed, and the patient lies on the bed in a supine position. The sensor is rotated into position such that the detector array surrounds the patient’s head. A head and neck support further insures patient comfort.

Stimulators

A comprehensive array of highly effective stimulus components are available for visual, auditory, and somatosensory stimulation. These stimulus devices are non-magnetic, thus do not interfere with the extremely sensitive magnetic measurements of MEG. Complex stimulus patterns may be generated to support both clinical and research studies.

The magnetically-silent visual stimulus delivery system consist of a high-performance commercial projector capable of projecting high-resolution images through an opening in the MSR wall, thereby eliminating electromagnetic interference. The image can be viewed from either the seated or supine position.

A non-magnetic auditory amplification and stimulus delivery system is provided by way of an amplifier, attenuator and electromechanical transducer located outside the MSR. The non-magnetic somatosensory stimulator applies tactile stimuli through electrical stimulation. The timing of the stimuli can be controlled through either external or internal timing signals. Four stimulus-output channels are provided, and can be activated either individually or in pairs.

Head Localization

During the MEG examination marker coils are placed on the patient’s head to record the position of the head during the exam. The nasion and the pre-auricular points are marked for identification during the digitization process. This information is later used to register the MEG source localization with the patient’s MRI.

EEG electrodes are also attached for epilepsy studies or to monitor heart rate, eye blinks or EMG. The location of the coils (and EEG electrodes if desired) are digitized. The process defines the head frame of reference. Then the shape of the patient’s head is digitized for the localization process.

The patient is then placed in the MEG system and made comfortable. Staff can monitor the patient via an intercom system and video monitor. During this completely painless and non-invasive exam the staff can view the real time MEG data long with the EEG data. A somatosensory, visual or auditory mapping study takes about an hour and a half to complete and an epilepsy exam about two to three hours. Once the study is completed, all of the coils are removed and the patient can leave with no restrictions. MEG source localizations are then overlaid onto the patient’s MRI and a report is generated for the referring physician.