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Improving the amplitude‐modulated control experiment for multislice continuous arterial spin labeling
Author(s) -
Werner Richard,
Norris David G.,
Alfke Karsten,
Mehdorn H. Maximilian,
Jansen Olav
Publication year - 2005
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.20443
Subject(s) - spins , bloch equations , amplitude , multislice , nuclear magnetic resonance , physics , dimensionless quantity , adiabatic process , pulse (music) , magnetization , computational physics , condensed matter physics , optics , mechanics , quantum mechanics , magnetic field , detector
The use of an amplitude‐modulated radiofrequency (RF) pulse for a control experiment is a proven method to control for off‐resonance effects in multislice continuous arterial spin labeling (CASL) experiments. This method is also known as double adiabatic inversion. The adiabaticity factor of a single half‐pulse, β 1/2 , and a new dimensionless parameter α, which is obtained from the labeling parameters and the flow velocity, are introduced. This makes it possible to distinguish three distinct cases: 1) With low α, a double inversion occurs. 2) With α ≥ ∼4, the efficiency with which the longitudinal magnetization is returned to the z ‐axis depends on the phase of the amplitude modulation at the time the spins cross the center of the labeling plane. 3) In the intermediate region, the efficiency shows undesirable fluctuations. In a Bloch equation simulation, three optimized parameter sets are determined. Near ideal performance should always be achieved by combinations of parameters for which β 1/2 ≥ ∼2 and α ∼ π/β 1/2 . The efficiency increases were realized in a volunteer study, showing the practical application of the suggested optimization. Magn Reson Med 53:1096–1102, 2005. © 2005 Wiley‐Liss, Inc.