Reduced vessel tone leads to vasodilation and decreased cerebral rigidity

Magnetic Resonance Elastography (MRE) measures elastic shear wave propagation in vivo to infer biomechanical properties non-invasively [Muthupillai, et al. (1995) Science;269:1854-1857.]. Models predict that tissue stiffness is influenced by changes of vascular properties [Parker, et al. (2016) PhysMedBiol;61:4890-4903.]. Cerebral blood supply is closely regulated by diameter changes of blood vessels. We here investigated the influence of vasodilation on cerebral brain stiffness with MRE. A healthy C57BL/6 mouse was anesthetized with isoflurane mixed in 100% O2. Vasodilation was induced by a hypercapnic challenge (isoflurane mixed in 95% O2 + 5% CO2). Brain stiffness was measured with a 3D spin-echo MRE sequence in a 7T animal MRI scanner under normocapnic and hypercapnic conditions. Vibration frequency was 1 kHz. Wave length and wave speed was observed to decrease significantly under hypercapnic conditions across the whole brain when compared to baseline. These changes correspond to a decrease in tissue ...