David Cohen, a physicist at the Massachusetts Institute of Technology and pioneer in the field, explained the phenomenon of biomagnetism and how scientists use magnetoencephalography (MEG) to measure these fields during Friday’s Jones Seminar at the Thayer School of Engineering.
Cohen, who has been called the “father of the MEG,” began the lecture by explaining the sources of biomagnetism, or magnetic fields produced by the human body. These magnetic fields result from currents produced by natural ions, as well as contaminate magnetic particles in the body.
Because of the relative magnitudes of these magnetic fields, MEG makes use of an extremely sensitive detector titled the Superconducting Quantum Interference Device (SQUID). MEGs are so sensitive, Cohen said, that they can detect the magnetic field generated by a spoonful of canned beans in a human stomach. However, these precise measurements cannot be made without first eliminating the background noise from larger external magnetic fields.
Cohen went on to differentiate between MEG and EEG (electroencephalography), the measurement of electrical brain activity. MEG is able to localize dipoles 50 percent better than EEG. Furthermore, Cohen characterized MEG as blind in the sense that it analyzes data using a smaller scope, thereby eliminating huge complexities in measurement. As a result, MEG can precisely quantify the strength of the magnetic field.
Thus far, MEG systems have contributed significantly to the study of direct current (DC) from the human body. They are also preferred over EEG systems when infants are the subjects. Because of the soft fontanelles in infants’ skulls, EEG analyses exhibit major distortion. MEG systems are not susceptible to the distortion caused by these soft spots. Additionally, MEG has shown success in localizing sources of activity for patients with epilepsy.
Cohen concluded by expressing interest in using multimodal imaging, the conjunction of fMRI and MEG, to reach new developments. Dartmouth already owns an fMRI system, and Dartmouth’s Thayer School of Engineering will join about 160 laboratories worldwide when it acquires a MEG system.