Sensitivity of MR phase shift to detect evoked neuromagnetic fields inside the head

Test object and human studies were conducted to determine the feasibility of detecting the evoked neuromagnetic field inside the head using MR phase shift imaging. Test-object studies involved pulsing a small variable current through the inner portion of a cylindrical object to determine the sensitivity of a 1.5 T MRI system. The sensitivity was then related to measurements of the same object by a SQUID neuromagnetometer. Also, preliminary human studies were conducted in the same 1.5 T system and images were acquired with and without auditory stimulation. The results of the test-object study suggest that detection of the in-vivo neuromagnetic field would require measurements of phase shifts of approximately 0.35 deg in the MRI scanner. The scanner used was measured to have a sensitivity of about 6.8 deg. Preliminary human studies were unsuccessful since no clear neuromagnetic pattern could be discerned above the noise or above several flow related phase artifacts.<
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