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New FOCI pulses with reduced radiofrequency power requirements
Author(s) -
Shen Jun,
Chen Zhengguang,
Yang Jehoon
Publication year - 2004
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.20134
Subject(s) - sinc function , specific absorption rate , rf power amplifier , excitation , radio frequency , main lobe , nuclear magnetic resonance , spin echo , physics , optics , materials science , magnetic resonance imaging , computer science , telecommunications , optoelectronics , medicine , amplifier , quantum mechanics , antenna (radio) , computer vision , cmos , radiology
Purpose To propose new frequency offset corrected inversion (FOCI) pulses with significantly reduced radiofrequency (RF) power deposition for spin echo imaging by incorporating the variable‐rate selective excitation (VERSE) schemes into the pulse design. Materials and Methods Two schemes are proposed to design the new FOCI pulses with dramatically reduced peak RF power requirements. In scheme A, the time‐dilation function is derived from a predefined adiabaticity factor modulation function. In scheme B, the time‐dilation function is predefined, while the adiabaticity factor is conserved. Results The new FOCI pulses are shown to be able to operate at reduced specific absorption rate (SAR), specifically at the same peak RF power as that of a five‐ or seven‐lobe sinc inversion pulse of the same duration. Using the new FOCI pulse, significant gain in sensitivity was observed in in vivo spin‐echo echo‐planar imaging, which was attributed to the improved refocusing slice profile. Conclusion The new FOCI pulses can replace the 180° five‐ or seven‐lobe sinc pulses in spin‐echo imaging with the same peak RF power requirement and significantly improved slice profile. J. Magn. Reson. Imaging 2004;20:531–537. © 2004 Wiley‐Liss, Inc.