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 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 singlecompartment 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 vertical bar 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. (C) 2016 International Society for Magnetic Resonance in Medicine