Separation of the vascular and tissue contributions to the T1rho change induced by brain activation

Introduction T1ρ is the spin-lattice relaxation time in the rotating frame during application of an on-resonance spin-locking pulse. Recently, we reported an activation induced decrease of R1ρ (=1/ T1ρ) at the parenchyma of cat visual cortex [1]. It has been proposed by Hulvershorn et al. in a previous human visual stimulation study at 3 T that such functional T1ρ change can largely be attributed to an increase of cerebral blood volume (CBV), though other effects may also contribute [2]. Since T1ρ of tissue water has been found to be sensitive to many physiological parameters such as intracellular pH level [3], macromolecular composition and density, it is of particular interest to investigate whether the functional decrease of R1ρ at the parenchyma has a significant contribution from the extravascular tissue, which may have a different signal source from the hemodynamic response. In this work, we measured the functional response of T1ρ with and without the suppression of the intravascular blood signal by injecting a contrast agent.