Luis Hernandez-Garcia1, Krishan Prem Kumar2, Jeremy Gam3
1FMRI laboratory, University of Michigan, Ann Arbor, MI, United States; 2FMRI laboratory, university of michigan, Ann Arbor, MI, United States; 3FMRI Laboratory, university of michigan, Ann Arbor, MI, United States
We present a simple method to map time-varying magnetic fields inside tissue using MRI. The method allows for imaging the spatial distribution of a broad spectrum of frequencies and only requires that the device in question be MR compatible and can be synchronized with the MR scanner, which can be usually be achieved via TTL lines. The main constraints of the method are that (1) it requires knowledge of the temporal characteristics of the magnetic field under scrutiny, and tight control of its timing; (2) it can only be used for low field amplitudes (in the order of a few Gauss) so that the phase gain can be kept within 0 and 2PI, which means that in most cases we must image a scaled down version of the desired field; (3) the frequency content of the waveform must be below the Larmor frequency of the tissues spins.