Characterization of pseudo-continuous arterial spin labeling: Simulations and experimental validation.

Purpose: To characterize pseudo-continuous arterial spin labeling (pCASL) through simulations of spin inversion and to discuss suitable parameter settings for measuring cerebral perfusion. Methods: Simulations of arterial spin inversion in pCASL were performed based on the Bloch equation. Both the labeling and the control condition of pCASL were analyzed separately, and the labeling efficiency, a, was calculated depending on the averages of both, the radiofrequency (RF) field amplitude and labeling gradient strength. The influence of additional parameters characterizing the pCASL pulse sequence, such as the interpulse interval, the RF duty cycle, and the labeling gradient, also were studied. An echo-planar imaging protocol utilizing a short repetition time was developed for experimental validation by estimating a in the internal carotid artery. Results: The effectiveness of the control condition of balanced pCASL crucially depends on both the labeling gradient amplitude and the RF duty cycle. The use of large values for both quantities improves the insensitivity to off-resonance gradients caused by magnetic field inhomogeneities. In addition, balanced and unbalanced pCASL become comparably effective. Conclusion: By use of appropriate parameter settings, labeling efficiencies of around 90% are feasible, independent of expected off-resonance gradients at 3T. Magn Reson Med 79: 1638-1649, 2018. (C) 2017 International Society for Magnetic Resonance in Medicine.