At the National Institute of Standards and Technology (NIST) scientists have been working on microfabricated atomic magnetometers capable of detecting faint magnetic fields. The devices, about 1cm3 in size, were taken to the Physikalisch Technische Bundesanstalt (PTB) in Berlin, Germany where supposedly resides the most magnetically isolated building in the world. Using the tiny magnetometers, investigators were able to detect the magnetic signature of human heartbeats, perhaps opening up the possibility for a new modality to complement ECG.
The NIST sensor—a tiny container of about 100 billion rubidium atoms in gas form, a low-power infrared laser, and optics—measured the heart’s magnetic signature in picoteslas (trillionths of a tesla). The tesla is the unit that defines magnetic field strength. For comparison, the Earth’s magnetic field is a million times stronger (measured in millionths of a tesla) than a heartbeat, and an MRI machine uses fields several million times stronger still (operating at several tesla).
In the experiments at PTB, the NIST sensor was placed 5 millimeters above the left chest of a person lying face up on a bed. The sensor successfully detected the weak but regular magnetic pattern of the heartbeat. The same signals were recorded using the "gold standard" for magnetic measurements, a SQUID (superconducting quantum interference device). A comparison of the signals confirmed that the NIST mini-sensor correctly measured the heartbeat and identified many typical signal features. The NIST mini-sensor generates more "noise" (interference) in the signal but has the advantage of operating at room temperature, whereas SQUIDs work best at minus 269 degrees Celsius and require more complicated and expensive supporting apparatus.
The new results suggest that NIST mini-sensors could be used to make magnetocardiograms, a supplement or alternative to electrocardiograms. The study also demonstrated for the first time that atomic magnetometers can offer sensing stability lasting tens of seconds, as needed for an emerging technique called magnetorelaxometry (MRX), which measures the magnetization decay of magnetic nanoparticles. MRX is used to localize, quantify and image magnetic nanoparticles inserted into biological tissue for medical applications such as targeted drug treatments.
Press release: NIST Mini-Sensor Traces Faint Magnetic Signature of Human Heartbeat…
Abstract in Applied Physics Letters: Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications
(hat tip: The Engineer)