Premium
Radiofrequency pulse design for the selective excitation of dissolved 129 Xe
Author(s) -
Leung General,
Norquay Graham,
Schulte Rolf F.,
Wild Jim M.
Publication year - 2015
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25089
Subject(s) - excitation , pulse (music) , xenon , chemistry , nuclear magnetic resonance , atomic physics , physics , optics , detector , quantum mechanics
Purpose To optimize radiofrequency (RF) pulses for the selective excitation of dissolved phase 129 Xe that take into account the very short T2*, while simultaneously, minimally exciting the much larger gas signal. Methods Numerical simulations of Shinnar le‐Roux pulses and binomial coefficient composite‐element pulses were performed and experimentally implemented on a 1.5 Tesla (T) clinical scanner. These were compared with pulses commonly used for short T 2 * imaging from the literature. The pulses were then experimentally tested in vivo with healthy volunteers inhaling hyperpolarized 129 Xe using nuclear MR spectroscopy on a 1.5T clinical scanner. Results Standard RF excitation pulses inadvertently excite the gas compartment, or are long enough that the T 2 * of the dissolved compartment deteriorates the received signal. Amplitude modulated binomial composite pulses perform well being short and having high selectivity, however, deteriorate at high amplifier gain setting. Composite pulses using pulse width modulation provide the desired frequency response even in these nonlinear, high gain regimes. Conclusion Composite pulses provide a means of very narrow band frequency selectivity in a short duration pulse that is well suited to dissolved 129 Xe imaging. Pulse width modulation maintains the desired frequency response even in the presence of amplitude distortion. Magn Reson Med 73:21–30, 2015. © 2014 Wiley Periodicals, Inc.