Warm Detectors Look At Brain Magnetism

The brain and heart both generate weak magnetic fields which, in ways different from electric fields, can reveal subtle clues about such maladies as epilepsy and arrhythmias. Sensitive magnetometers, based on superconducting quantum interference devices (SQUIDs), have been used to prepare detailed magnetoencephalograms (MEGs). Unfortunately, these devices require liquid helium and all its associated cryogenic equipment.

Michael Romalis, a Princeton University physicist, detects the brain's faint magnetic fields using instead a vessel filled with potassium atoms, which have been polarized by a laser beam. The brain fields cause the potassium atoms to precess in a measurable way. Already, Romalis (romalis@princeton.edu) says, his device has attained a sensitivity 30 times better than previous atomic magnetometers used for biosensors, and a spatial resolution comparable to that for SQUIDs, with the prospect of improving by another factor of ten.

In a related paper, Romalis's group in collaboration with Karen Sauer from George Mason University used a different kind of potassium magnetometer to detect radio-frequency signals generated by ammonium nitrate (which is often used in explosives) with a sensitivity some 10 times better than with conventional devices.

Xia et al. and Lee et al., two articles in Applied Physics Letters, 20 November 2006
More information from Romalis's Web page