Impact of calibration method on CBF quantification using multiple post-labeling-delay PASL

Absolute CBF quantification using ASL requires the normalization of the magnetization difference images by the equilibrium magnetization of arterial blood, which is usually extrapolated from the equilibrium magnetization measured in tissue. Although different calibration methods have been previously compared, a number of subtle processing options made in their practical implementation are often assumed or overlooked, compromising the utility of absolute quantification. We systematically compared different calibration methods and associated options in multiple post-labeling-delay pulsed ASL and found that they can severely impact CBF quantification. Our results highlight the need for consistent calibration pipelines for CBF quantification using ASL.