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

Test object and human feasibility studies were conducted to determine if the evoked neuromagnetic field could be detected inside the head using MR (magnetic resonance) phase shift imaging. A small variable current was pulsed through the inner portion of a cylindrical object to determine the sensitivity of a 1.5 T MRI (magnetic resonance imaging) system, and the sensitivity was then related to measurements of the same object by a SQUID (superconducting quantum interference device) neuromagnetometer. Preliminary human studies were conducted in the same 1.5 T system, and images were acquired with and without an auditory stimulation. The results of the test object study show that detection of the in-vivo neuromagnetic field requires measurements of phase shifts ~0.35 deg in the MRI scanner. The scanner used was measured to have a sensitivity of about 6.8 deg. The preliminary human studies were unsuccessful since no neuromagnetic pattern could be discerned above the noise or above several flow-rated phase artifacts