Premium
Velocity‐selective RF pulses in MRI
Author(s) -
de Rochefort Ludovic,
Maître Xavier,
Bittoun Jacques,
Durand Emmanuel
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.20751
Subject(s) - excitation , spins , flip angle , physics , position (finance) , optics , wafer , computational physics , group velocity , k space , thermal velocity , series (stratigraphy) , fourier transform , flow velocity , nuclear magnetic resonance , flow (mathematics) , mechanics , magnetic resonance imaging , condensed matter physics , quantum mechanics , medicine , optoelectronics , finance , economics , radiology , paleontology , biology
A family of velocity‐selective pulses consisting of a series of RF hard pulses followed by bipolar gradients was designed. The succession of required pulses was deduced using a k ‐space approach within a small tip‐angle approximation. Fourier transform of the desired velocity excitation determined the flip‐angle series, and the corresponding position in the generalized k ‐space identified the bipolar‐gradient first moments. Spins from any velocity class can be selected. To illustrate this approach we designed and experimentally tested a velocity‐slice selection that is analogous to standard spatial‐slice selection but involves excitation of spins moving at a chosen velocity (velocity‐slice center) and within a given interval (velocity‐slice thickness). The assumed approximation does not limit the design to small angles, because velocity selection still holds for angles up to 90°. Velocity slices were experimentally selected, centered on velocities ranging from −1 m s −1 to 1 m s −1 with a velocity‐slice thickness of 0.4 m s −1 . The experimental velocity‐slice profile was assessed and the flow was quantified. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.