Measurement of magnetic susceptibility change in fMRI using SSFP technique

Abstract

A fast SSFP gradient echo sequence applied to the measurement of the field inhomogeneity is presented. As it is known, SSFP sequence with a suitable adjustment allow us to measure precession angle which is directly related to the field inhomogeneity. For example, combining the two pulses (known as FID and Echo) in FADE(Fast Acquisition Double Echo) sequence, one can obtain the interference term which represents the precession angle. It has been found that a high resolution magnetic field map can be obtained by the proposed technique with the scan time less than 10 seconds which is considerably shorter than those of other field mapping techniques. In the measurement of the field inhomogeneity including the susceptibility-induced one, fast field mapping is desired to reduce the examination time in human study. Applications of the method are, among others, susceptibility dependent functional magnetic resonance imaging(fMRI). When it is applied to fMRI, direct susceptibility measurement during neural stimulation is possible. In this paper, simulation results and experimental results obtained with 2.0 Tesla MRI system are also presented.