Theory of sleep/wake cycles affecting brain elastography

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Brain elastography is increasingly used clinically, but baseline properties and changes over time are poorly understood.
• The mechanisms influencing brain viscoelasticity, particularly during different physiological states, require further investigation.

Purpose of the Study:

• To investigate the relationship between brain viscoelasticity and physiological state (awake vs. sleep) in a mouse model.
• To develop and validate a rheological model explaining elastographic changes based on fluid dynamics in the brain's vascular and glymphatic systems.

Main Methods:

• Reverberant shear wave elastography combined with optical coherence tomography in a mouse model.
• Comparison of shear wave speed (stiffness) in awake versus sleep states.
• Development of a biphasic microchannel flow model incorporating vascular and glymphatic systems.

Main Results:

• A ~12% change in shear wave speed (brain stiffness) was observed between awake and sleep states across the cortical volume.
• The microchannel flow model successfully predicted measured shear wave speeds by adjusting glymphatic fluid volume proportional to sleep/wake state.
• Model parameters are linked to anatomical measures and fluid dynamics principles like Murray's Law.

Conclusions:

• Brain elastography is sensitive to physiological state changes, particularly fluid regulation within the glymphatic system.
• The developed rheological model provides a mechanistic link between fluid dynamics and brain viscoelasticity.
• Findings have implications for interpreting clinical brain elastography, highlighting the influence of vascular and glymphatic system regulation.