Magnetoencephalography System and Method for 3D Localization and Tracking of Electrical Activity in Brain
Magnetoencephalogram techniques passively measure the magnetic fields emanating from neuronal sources in the brain. Current magnetoencephalograph (MEG) systems require supercooled (for example, helium-cooled) devices, a shielded room, heavy arrays of multichannel sensors, and a liquid-helium apparatus.
APL researchers have developed an inventive MEG system that is lightweight and portable, operates at room temperature, provides 3-D localization and tracking, is safer (in that it does not use pressure vessels or a high-energy apparatus), and can be applied to subjects in a variety of positions and circumstances. The system can provide data for other imaging algorithms such as near-field holography.
As shown in Fig. 1, the invention comprises a shell or helmet that has a high magnetic permeability and contains magnetic sensors; the shell or helmet fits over and around the head to sense the magnetic fields generated by electrical activity in the brain. The magnetic sensor signals are transmitted to a computer that calculates the location and time evolution track of the electrical currents of brain activity. The brain activity may be part of normal brain activity without external stimuli; a response to external stimuli such as a visual evoked response (VER), an auditory evoked response (AER), or a somatosensory evoked response (SER); or a result of an electrical discharge from pathological foci due to brain dysfunction.
More particularly, the portable MEG system includes:
- Several sets of magnetic sensors that are arranged in the three-axis magnetic gradiometer (3XG) configuration in order to map brain activity in several planes so that information can be collected in 3-D
- New room-temperature magnetometers and gradiometers with sensitivities better than 100 fT/sqrt(Hz)
- Auxiliary reference sensors (R) to monitor background magnetic noise and magnetic signals from the human subjectís heart, breathing, somatoreactions, etc., and to provide adaptive feedback to reduce these extraneous signals, which blur the MEG-targeted signals
- Calibrated magnetic dipoles (S), which are placed around the head for stereotactic reference frame positioning of magnetic signals
- Additional coils (not shown) to provide signals to cancel the ambient magnetic fields (i.e., Earthís, geomagnetic) by impressing coil currents as feedback from ambient field reference sensors (R)
- Embedding of stimulus for VERs and AERs in the helmet
- A set of computer algorithms for the calibration, localization and tracking, adaptive feedback noise reduction, and stereotactic functions
Dr. G. R. Jacobovitz
Phone: (443) 778-9899