20 April 2012
Miniature sensor measures magnetic activity in human brain
A miniature atom based magnetic sensor developed by the National Institute of Standards and Technology (NIST) has been used to measure alpha waves in the brain associated with a person opening and closing their eyes, as well as signals resulting from stimulation of the hand.
The sensor could be used for biomedical applications such as studying mental processes and advancing the understanding of neurological diseases.
Measurements were compared with the signals recorded by a SQUID (superconducting quantum interference device) – the world's most sensitive commercially available magnetometer. Although currently less sensitive, the NIST sensor is said to have the potential for comparable performance while offering potential advantages in size, portability and cost.
The study indicated that the mini sensor could be useful in magnetoencephalography (MEG), a procedure that measures the magnetic fields produced by electrical activity in the brain. MEG is used for research on perceptual and cognitive processes in healthy subjects as well as screening of visual perception in newborns and mapping brain activity prior to surgery to remove tumours or treat epilepsy.
MEG currently relies on SQUID arrays mounted in heavy helmet shaped flasks containing cryogenic coolants. The NIST sensor is about the size of a sugar cube, and unlike SQUIDs, can operate at room temperature, so it could enable lightweight and flexible MEG helmets. It would also be less expensive to mass produce than typical atomic magnetometers.
"We're focusing on making the sensors small, getting them close to the signal source, and making them manufacturable and ultimately low in cost," said NIST co author Svenja Knappe. "By making an inexpensive system you could have one in every hospital to test for traumatic brain injuries and one for every football team."
The mini sensor consists of a container of about 100billion rubidium atoms in a gas, a low power infrared laser and fibre optics for detecting the light signals that register magnetic field strength by absorbing light.
In testing the mini sensor measured magnetic signals of about 1 picotesla (trillionths of a tesla). Scientists expect to boost its performance by increasing the amount of light detected. Calculations suggest it could soon match the sensitivity of SQUIDs.
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