Impact of tissue T1 on perfusion measurement with arterial spin labeling

Purpose Arterial spin labeling (ASL) may provide quantitative maps of cerebral blood flow (CBF). Because labeled water exchanges with tissue water, this study evaluates the influence of tissue T1 on CBF quantification using ASL. Methods To locally modify T1, a low dose of manganese (Mn) was intracerebrally injected in one hemisphere of 19 rats (cortex or striatum). Tissue T1 and CBF were mapped using inversion recovery and continuous ASL experiments at 4.7T. Results Mn reduced the tissue T1 by more than 30% but had little impact on other tissue properties as assessed via dynamic susceptibility and diffusion MRI. Using a single‐compartment model, the use of a single tissue T1 value yielded a mean relative ipsilateral (Mn‐injected) to contralateral (noninjected) CBF difference of −34% in cortex and −22% in striatum tissue. With a T1 map, these values became −7% and +8%, respectively. Conclusion A low dose of Mn reduces the tissue T1 without modifying CBF. Heterogeneous T1 impacts the ASL estimate of CBF in a region‐dependent way. In animals, and when T1 modifications exceed the accuracy with which the tissue T1 can be determined, an estimate of tissue T1 should be obtained when quantifying CBF with an ASL technique. Magn Reson Med 77:1656–1664, 2017. © 2016 International Society for Magnetic Resonance in Medicine