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1 2009

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Squid system for meg and low field magnetic resonance

Burghoff M., Albrecht H. H., Hartwig S., Hilschenz I., Körber R., Sander Thömmes T., Scheer H. J., Voigt J., Trahms L.

Metrology and Measurement Systems

2009

Vol. 16, nr 3

371-375

A SQUID magnetometer system was developed for measuring sustained brain activity by magnetoencephalography (DC-MEG) and to record the free precession decay of protons (FPD) of the human brain at very low fields. The SQUID system has a white noise level of about 4 fT/√Hz. To generate the MR signal, two magnetic fields are used: a static polarisation field of a few mT and a static detection field of a few microtesla. To test the spectral resolution of the system, we measured the FPD of protons in distilled water having a spectral line width of about 156 mHz with an instrumental resolution of 2 mHz. The proton resonance line width of the human brain was found to be about 3.0 Hz. Using the same SQUID system we recorded a DC-MEG signal with an amplitude of about 1.5 pT upon motor stimulation. On the basis of these data, we discuss the possibility of detecting a shift of the resonance line due to the superposition of the neuromagnetic field generated by sustained brain activity.