High-field continuous arterial spin labeling with long labeling duration: reduced confounds from blood transit time and postlabeling delay.

In quantitative perfusion imaging using arterial spin labeling, variable blood transit times and postlabeling delays are two confounding factors that may compromise the accuracy of perfusion quantifications. In this study, theoretical analyses and experimental data at 9.4 T demonstrate that increasing labeling duration not only enhances the contrast of the arterial spin labeling signal but also minimizes the effect of variable postlabeling delays in multislice arterial spin labeling acquisitions. With a labeling duration of 6.4 sec, arterial spin labeling signal acquired in multislice mode (11 slices) is very similar to that acquired in single-slice mode. Previous studies have shown that inserting a delay between the spin labeling pulse and the image acquisition pulse could reduce confounds resulting from variable blood transit times at the expense of arterial spin labeling sensitivity. Our simulations suggest that enhancing the contrast of arterial spin labeling signal offers the opportunity for extending the postlabeling delay to a longer duration, minimizing systematic errors associated with a wide range of blood transit times, which could have significant implications for applying arterial spin labeling techniques to perfusion imaging of pathological conditions in animal models.