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Susceptibility compensated fMRI study using a tailored RF echo planar imaging sequence
Author(s) -
Chung JunYoung,
Yoon Hyo Woon,
Kim YoungBo,
Park Hyun Wook,
Cho ZangHee
Publication year - 2009
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.21397
Subject(s) - pulse (music) , echo planar imaging , phase (matter) , excitation , signal (programming language) , nuclear magnetic resonance , pulse sequence , functional magnetic resonance imaging , magnetic resonance imaging , physics , materials science , computer science , optics , medicine , quantum mechanics , detector , radiology , programming language
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 TRF 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 2π. We demonstrate theoretically that the maximum phase distribution can also be reduced to π rather than 2π, 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 π phase distribution. Results Thorough experimental comparisons were also made between the TRF quadratic excitation with a π 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 inferior temporal cortex, were increased, suggesting that the technique could be a useful adjunct to fMRI. J. Magn. Reson. Imaging 2009;29:221–228. © 2008 Wiley‐Liss, Inc.