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Reducing contamination while closing the gap: BASSI RF pulses in PASL
Author(s) -
Warnking Jan M.,
Pike G. Bruce
Publication year - 2006
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.20843
Subject(s) - amplitude , spins , materials science , pulse sequence , saturation (graph theory) , chemistry , nuclear magnetic resonance , optics , atomic physics , physics , mathematics , condensed matter physics , combinatorics
Bandwidth‐modulated selective saturation and inversion (BASSI) pulses are a class of frequency‐ and gradient‐modulated radiofrequency (RF) pulses, derived from the hyperbolic secant pulse by temporal variation of the bandwidth parameter. These pulses afford optimal amplitude modulation, achieving uniform and highly selective profiles at any effective flip angle. In this paper, BASSI pulses are parameterized to obtain low RF energy pulsed arterial spin labeling (PASL) label pulses with minimal contamination of static spins outside the label region and highly selective PICORE/QUIPSS II saturation pulses allowing for small label gaps. They are compared to frequency offset corrected inversion (FOCI) label pulses and sinc saturation pulses in simulations and a phantom experiment. Drawing on the outstanding selectivity of bandwidth‐modulated saturation pulses, a new noninvasive method to measure in vivo the contamination effects due to direct and indirect saturation of static spins by the label pulse is presented. In an in vivo study on four subjects, contamination effects in a QUIPSS II PASL implementation based on BASSI pulses are compared to those present in a state‐of‐the‐art Q2TIPS sequence employing a FOCI label pulse. Residual contamination in the QUIPSS II/BASSI sequence is shown to be reduced by a factor of 3, compared to the Q2TIPS/FOCI sequence. In vivo human perfusion images obtained with a label gap of only 2 mm are presented. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.