Through thick and thin : improved transcranial focused ultrasound transmission estimates with acoustic simulation and magnetic resonance imaging
Abstract/Contents
- Abstract
- Transcranial focused ultrasound is a promising technique for non-invasively treating brain disorders. During treatments, acoustic energy is focused through the intact skull to a millimeter-sized target. This can result in a variety of effects on tissue, ranging from mechanical perturbations to necrosis, depending on the duration, pulsing scheme, and intensity of the sonications. However, the skull is a substantial obstacle to safe and effective treatments. It is highly attenuative, absorbing and scattering the majority of the transmitted ultrasound due to its strongly heterogeneous composition. The consequence of this could be an aberrated focal spot which might be shifted from the intended target. In this dissertation, we demonstrate the necessity for accurate estimates of acoustic intensity delivered into the brain for transcranial focused ultrasound treatments, such as ultrasound-mediated blood-brain barrier opening. We discuss and propose improvements to two promising approaches for estimating in situ acoustic intensity, one using magnetic resonance imaging and another using acoustic simulation. Magnetic resonance acoustic radiation force imaging is a phase-contrast imaging technique where motion-encoding gradients are applied to encode tissue displacement induced by the acoustic radiation force in the phase of the image, enabling localization of the focal spot. As the acoustic radiation force is proportional to the applied acoustic intensity, measured displacements could potentially be used to estimate the acoustic intensity at the target. However, variable brain stiffness remains an obstacle. We demonstrate that viscoelasticity information from magnetic resonance elastography could be used in combination with displacement estimates to more accurately predict the delivered acoustic intensity. Finally, another approach for estimating acoustic transmission through the skull is by simulating acoustic propagation using the hybrid angular spectrum method. While this method is computationally efficient, its assumptions of normal incidence and weak heterogeneity in the medium may not be suitable for transcranial applications. We demonstrate the limitations of this method using a set of numerical benchmarks, and we propose adapting it toward transcranial applications by extending the implementation of acoustic attenuation into the spatial-frequency domain. The improvements presented here have the potential to enable clinicians and researchers to more accurately determine how much acoustic energy is being delivered to which regions of the brain, allowing them to focus on exploring the treatment parameter space rather than being uncertain about whether ultrasound is even reaching the intended target at power levels relevant for therapy. We hope that this work moves the field towards safer and more effective transcranial focused ultrasound therapies.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2023; ©2023 |
| Publication date | 2023; 2023 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Li, Ningrui |
|---|---|
| Degree supervisor | Pauly, Kim Butts (Kim Rosemary Butts) |
| Thesis advisor | Pauly, Kim Butts (Kim Rosemary Butts) |
| Thesis advisor | Dahl, Jeremy J, 1976- |
| Thesis advisor | Nishimura, Dwight George |
| Thesis advisor | Pauly, John (John M.) |
| Degree committee member | Dahl, Jeremy J, 1976- |
| Degree committee member | Nishimura, Dwight George |
| Degree committee member | Pauly, John (John M.) |
| Associated with | Stanford University, School of Engineering |
| Associated with | Stanford University, Department of Electrical Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Ningrui Li. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2023. |
| Location | https://purl.stanford.edu/nh533gk4852 |
Access conditions
- Copyright
- © 2023 by Ningrui Li
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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