In patients with acute stroke with an unknown time of onset, intravenous alteplase guided by a mismatch between diffusion-weighted imaging and FLAIR in the region of ischemia resulted in a significantly better functional outcome and numerically more intracranial hemorrhages than placebo at 90 days. (Funded by the European Union Seventh Framework Program; WAKE-UP ClinicalTrials.gov number, NCT01525290; and EudraCT number, 2011-005906-32 .).

Normal aging is associated with diminished brain perfusion measured as cerebral blood flow (CBF), but previously it is difficult to accurately measure various aspects of perfusion hemodynamics including: bolus arrival times and delays through small arterioles, expressed as arterial-arteriole transit time. To study hemodynamics in greater detail, volumetric arterial spin labeling MRI with variable postlabeling delays was used together with a distributed, dual-compartment tracer model. The main goal was to determine how CBF and other perfusion hemodynamics vary with aging. Twenty cognitive normal female and 15 male subjects (age: 23-84 years old) were studied at 4 T. Arterial spin labeling measurements were performed in the posterior cingulate cortex, precuneus, and whole brain gray matter. CBF declined with advancing age (P < 0.001). Separately from variations in bolus arrival times, arterial-arteriole transit time increased with advancing age (P < 0.01). Finally, women had overall higher CBF values (P < 0.01) and shorter arterial-arteriole transit time (P < 0.01) than men, regardless of age. The findings imply that CBF and blood transit times are compromised in aging, and these changes together with differences between genders should be taken into account when studying brain perfusion. Magn Reson Med 68:912-922,

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 pulsed ASL sequence with multi-echo 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 has been collected from healthy volunteers on a 3 Tesla system. The mean transfer time parameter Tbl→ex (blood- to extravascular compartment transfer time) has been derived voxel-wise by non-linear least-squares fitting. Results Whole-brain maps of Tbl→ex show stable results in cortical regions, yielding different values depending on brain region. The mean value across subjects and ROIs in grey matter is 440±30 ms. 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 cerebro-vascular diseases.

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The use of ASL with multiple TI allows the contrast-free assessment of hemodynamic impairment in ischemic stroke patients. Quantitative ASL perfusion analysis reliably demonstrates areas of delayed BAT and reduced CBF matching findings of DSC.