Weak magnetic fields produced by the brain and the heart can provide valuable diagnostic and research information. So far SQUID magnetometers have been used for detection of biological magnetic fields from the brain (MEG) and the heart (MCG). These techniques help in diagnosis of epilepsy, cardiac arrhythmias, and other diseases. They are also used in functional studies of the brain. We are working with the Princeton Center for Brain, Mind, and Behavior to demonstrate the potential of atomic spin magnetometers in these applications.
Atomic spin magnetometers have a number of advantages over SQUID magnetometers:
In magnetic field imaging applications, the magnetic field at many points in a volume is measured. By measuring the field gradients precisely, it is possible to reconstruct the location of electric currents in an external volume.
For a detailed description of how the atomic magnetometer works, please refer to the magnetometer page. In imaging applications, the magnetic field is measured at the intersection of the pump and probe beams within the cell. A 1D or 2D image of the magnetic field can be obtained by projecting a wide probe beam onto a 1D or 2D photodiode array. The average magnetic field along a chord of the probe beam correspond to an intensity measurement at a pixel in the photodiode array.
We have demonstrated the operation of a 7 point gradient measurement using a 1D photodiode array. We measured a 100 fT magnetic field generated by a loop of wire positioned 5.3 cm away from the cell. The measured field gradient correctly determined the location of the loop.