Accounting for Dispersion in Arterial Spin Labeling Using the Mass Transport Model: Validation Using the Arterial Input Function

Introduction: Dispersion of labelled blood water is a recognised issue in the quantification of cerebral blood flow (CBF) using arterial spin labelling (ASL). The ASL signal measured in the tissue is the result of labelled blood water, described by an arterial input function (AIF), undergoing exchange with the extra-vascular space [1]. Dispersion occurs during the transit of the blood along the arteries and is thus seen in the AIF. The most widely used standard model [1] does not account for flow dispersion, assuming a uniform transport of the bolus. A number of models for dispersion have been proposed [2, 3], however they have each only included a relatively simple description of the dispersive process. Recently a mass transport model (MTM) of the dispersion of a bolus of labelled blood within an artery has been presented [4]. Results using the MTM to quantify CBF indicated that neglecting dispersion could lead to up to 60% underestimation. However, it was not possible to verify the accuracy of the MTM to describe the effects of dispersion using conventional ASL measurements, since the tissue signal is a result of both AIF and local exchange kinetics. Here we sought to validate the MTM description of the effects of dispersion by examining data in which measurements of the AIF itself were available.