CEE Seminar - Stressing the Strain in Transcranial Ultrasound Simulation

Transcranial ultrasound stimulation (TUS) has the promise of modulating deep brain structures with small focal spots. Early work by Fry (Science 1958) in modulating the visual system is reproducible and yielding valuable insights due to the extensive knowledge of the visual system and easy accessibility to study it. There is a multitude of new studies showing clear modulation in regions across the brain. We are gaining understanding the role of the auditory confound and how to mitigate it. The importance of planning with simulations is clear, as is the value of imaging the focal spot with MRI to verify targeting. MR-compatible systems are providing the ability to use functional MRI.
In terms of mechanism, research indicates that neurons in the central nervous system have ion channels that are endogenously mechanosensitive, such that focally applying gentle pressure waves with TUS can cause ion channel flux and affect firing activity (Yoo et al., 2022). An active area of research is understanding what type of mechanical effect, is needed, be it shear strain or normal strain, and how to build simulations of strain into planning simulations (Nafchi-Ardebili 2024). Lastly, we will build an argument that the MR imaging of the focal spot, which depends on the acoustic radiation force, may be reflective of the strains in the tissue, as was seen in a large animal model (Mohammadjavadi 2022).