Impact of tissue T 1 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 T 1 on CBF quantification using ASL. Methods To locally modify T 1 , a low dose of manganese (Mn) was intracerebrally injected in one hemisphere of 19 rats (cortex or striatum). Tissue T 1 and CBF were mapped using inversion recovery and continuous ASL experiments at 4.7T. Results Mn reduced the tissue T 1 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 T 1 value yielded a mean relative ipsilateral (Mn‐injected) to contralateral (noninjected) CBF difference of −34% in cortex and −22% in striatum tissue. With a T 1 map, these values became −7% and +8%, respectively. Conclusion A low dose of Mn reduces the tissue T 1 without modifying CBF. Heterogeneous T 1 impacts the ASL estimate of CBF in a region‐dependent way. In animals, and when T 1 modifications exceed the accuracy with which the tissue T 1 can be determined, an estimate of tissue T 1 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