T2-based arterial spin labeling measurements of blood to tissue water transfer in human brain.

PURPOSE: To investigate blood to tissue water transfer in human brain, in vivo and spatially resolved using a T2-based arterial spin labeling (ASL) method with 3D readout. MATERIALS AND METHODS: A T2-ASL method is introduced to measure the water transfer processes between arterial blood and brain tissue based on a 3D-GRASE (gradient and spin echo) pulsed ASL sequence with multiecho readout. An analytical mathematical model is derived based on the General Kinetic Model, including blood and tissue compartment, T1 and T2 relaxation, and a blood-to-tissue transfer term. Data were collected from healthy volunteers on a 3 T system. The mean transfer time parameter T(bl → ex) (blood to extravascular compartment transfer time) was derived voxelwise by nonlinear least-squares fitting. RESULTS: Whole-brain maps of T(bl → ex) show stable results in cortical regions, yielding different values depending on the brain region. The mean value across subjects and regions of interest (ROIs) in gray matter was 440 ± 30 msec. CONCLUSION: A novel method to derive whole-brain maps of blood to tissue water transfer dynamics is demonstrated. It is promising for the investigation of underlying physiological mechanisms and development of diagnostic applications in cerebrovascular diseases.