Miniature magnetic sensor opens new era for neurology
12 June 2012
A new type of magnetic field sensor, called a chip-scale
atomic magnetometer (CSAM), uses miniaturized optics for measuring
absorption changes in a rubidium gas cell caused by magnetic fields.
Developed by the US National Institute of Standards and Technology,
the sensor has applications in magnetoencephalography (MEG), the
study of the brain's magnetic field and the underlying neurology.
The sensor has passed a sensitivity test carried out by
Physikalisch-Technische Bundesanstalt (PTB) in a magnetically
shielded room. It was able to detect both spontaneous and stimulated
magnetic fields of the brain.
Magnetic sensor the size of a sugar cube
electrical and optical lines.
Up to now the measurement of very weak magnetic fields was the
domain of cryoelectronic sensors, the so called superconducting
quantum interference device (SQUID). They can be considered as the
"gold standard" for this application, but they have the disadvantage
to operate only at very low temperatures close to absolute zero.
This makes them expensive and less versatile compared to CSAMs.
Even though at present CSAMs are still less sensitive
compared to SQUIDs, measurements as accurate as SQUIDs, but at lower
costs, might eventually become reality. Due to the cooling
requirements, SQUIDs have to be kept apart from the human body by a
few centimeters. In contrast, CSAMs can be attached close to the
human body. This increases the signal amplitude as the magnetic
field from currents inside the human body decays rapidly with
Magnetoencephalography (MEG) enables the characterization of
neuronal currents, which has gained importance during the last few
years for neurologists and neuroscientists. Objective indicators of
psychiatric disorders as well as age dependent brain diseases, are
urgently needed for the support clinical diagnostics.
Already in 2010 scientists from NIST and PTB had successfully
tested the performance of an earlier version of the present CSAM by
measurements of the magnetic field of the human heart. For the
present study the sensor was positioned about 4 mm away from the
head of healthy subjects. At the back of the head, the magnetic
fields of alpha waves were detected, a basic brain rhythm which
occurs spontaneously during relaxation. In another measurement the
brain fields due to the processing of tactile stimuli were
T. Sander-Thömmes, J. Preusser, R. Mhaskar, J. Kitching, L.
Trahms, S. Knappe: Magnetoencephalography with a Chip-Scale Atomic
Magnetometer. Biomedical Optics Express Vol. 3 Issue 5, pp.981-990
PTB-NIST-Experiment of 2010: S. Knappe, T.H. Sander, O. Kosch, F.
Wiekhorst, J. Kitching and L. Trahms. Cross-validation of
microfabricated atomic magnetometers with SQUIDs for biomagnetic
applications. Applied Physics Letters. 97, 133703 (2010);
doi:10.1063/1.3491548. Online publication: Sept. 28, 2010.