Impact of tissue T₁ on perfusion measurement with arterial spin labeling

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.

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.

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.

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.