A multichannel device for cardiac magnetic field imaging (cMFI)

NEWS: FRAP makes title page of Applied Physics Letters in October 2009. (see larger picture)

 SCOPE: Many physiological processes in the human body involve the flow of electrical currents, which generate time-varying magnetic fields. Even the strongest of such biomagnetic fields, the one produced by the beating human heart, barely reaches 100 pT outside the chest, less than a millionth of the geomagnetic field and orders of magnitude weaker than typical magnetic noise fields. Today's standard detector for biomagnetic fields is the superconducting quantum interference device (SQUID). The fact that SQUIDs require cooling to 77 K or 4 K contributes to the slow acceptance of biomagnetic diagnostics as a routine medical tool, despite the proven advantages of this non-invasive technique in a growing number of applications.

PAST: As an alternative to SQUIDs, we have developed room-temperature magnetometers based on optical pumping, with sufficient sensitivity, temporal and spatial resolution to record human magnetocardiograms (MCG) in a weakly shielded environment. The magnetometers use double (optical and magnetic) resonance in paraffin-coated Cs vapor cells driven by light from a diode laser. In the early days we constructed two-dimensional maps of human cardiomagnetic signals by stepping a first order gradiometer (consisting of two sensors) across the chest. the obtained cMFI maps have a quality that is comparable to SQUID data. Such laser-optical sensors have the potential to make biomagnetic diagnostics and therapy control convenient and cost-effective and therefore more widely available.

PRESENT: In recent years we have developed a multichannel system consisting of 25 individual sensors that allow recording cMFI maps from simultaneaous measurements on 19 points over the chest. The sensors arrangement is shown in the picture here below; one can see a part of the bed where people are lying during the measurement. Typical measurement times are of the order of two minutes (we need few minutes more to position the patient in the best centered way with respect to the apparatus).

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