Quantification of errors in cerebral blood flow measurements due to dispersion in arterial spin labelling.

The accuracy of cerebral blood flow (CBF) measurements using arterial spin labelling (ASL) is particularly affected by dispersion. In spite of this, however, the current recommended implementation of ASL - the white paper (WP) - does not account for dispersion, which leads to the introduction of errors in CBF. In fact, these errors are also likely to vary with the arterial transit time (ATT), which is the transport time from the labelling region to the tissue. Using pseudo-continuous ASL, this study assesses a variety of dispersion models in comparison with the WP quantification formula, enabling the errors introduced by the WP to be quantified. In particular, this study shows that the WP quantification only holds for ATTs below 1.25s - and that this ATT value reduces further as dispersion occurs. The levels of dispersion beyond which the WP introduces significant error are also quantified, such that provided the dispersion levels fall below the thresholds determined in this study, the WP can still measure CBF with reasonable accuracy.