Susceptibility Compensated fMRI Study Using a Tailored RF Echo Planar Imaging Sequence

Abstract

Purpose: To implement a method using a tailored radiofrequency (TRF) pulse with a quadratic phase profile to recover susceptibility-induced signal losses in gradient-recalled echo-planar images (EPI). Materials and Methods: A functional magnetic resonance imaging (fMRI) experiment for compensation of susceptibility artifacts. known as the TRIF pulse EPI sequence (TRF-EPI), was used. TRF pulse compensates the susceptibility effect with a reduced signal-to-noise ratio (SNR) to one-half when the maximum phase distribution is 2 pi. We demonstrate theoretically that the maximum phase distribution can also be reduced to 7 rather than 2 pi. improving the SNR accordingly. An analysis was conducted comparing this newly proposed strategy using a standard RF excitation with a linear phase distribution and a quadratic TRF excitation with a pi phase distribution. Results: Thorough experimental comparisons were also made between the TRF quadratic excitation with a pi phase profile and conventional EPI with a standard excitation in human subjects during ventral brain activation. Conclusion: With reduced maximum phase distribution in the TRF pulse. signals in the susceptibility-affected areas, such as the orbitofrontal and interior temporal cortex. were increased. suggesting that the technique Could be a useful adjunct to fMRI.