Focused ultrasound surgery (FUS) describes a treatment modality in which ultrasound energy is delivered to a targeted tissue site to achieve a therapeutic effect. FUS has already gained regulatory approval in the U.S. for treating uterine fibroids, pain palliation for bone metastases, and prostate ablation. Other applications including liver cancer and neurosurgery remain active topics for clinical trials and research. The appeal of FUS is clear: Nonionizing energy can be delivered to a treatment site noninvasively. Ultrasound can be used as a tool to induce a range of therapeutic effects, including thermal ablation, enhanced drug delivery, and mechanical disintegration of soft tissues with precise boundaries. However, in order to fully realize the clinical potential of FUS, capabilities should be developed for patient-specific treatment planning that is comparable to what is performed in radiotherapy. At present, typical treatment planning for abdominal targets remains unsophisticated; rather than utilizing detailed imaging information from each patient in conjunction with full- wave simulations to predict in situ pressure and temperature fields, treatments generally rely on real-time feedback from MR thermometry to customize the therapy. This approach does not depend explicitly on calibration of the ultrasound source and can be successful; however, accurate control of thermal treatments can be difficult while non-thermal treatments that utilize nonlinear fields and cavitation require an alternate approach. To improve the safety and effectiveness of FUS for abdominal targets, this project seeks to develop and test strategies for predicting in situ pressure and temperature fields. To address the underlying challenges, acoustic holography is a tool that has unique capabilities: It provides an efficient way to capture ultrasound field information in 3D from measurements in 2D. In addition, backprojection from a measured hologram can be used to reconstruct the vibrations at the transducer surface, thereby defining an accurate boundary condition for modeling wave propagation in any known medium to predict the in situ field at any given output level.
The first aim i s to reduce the time required for recording an accurate hologram from many hours to tens of minutes or less, using continuous scanning and specially designed array hydrophones.
The second aim i s to optimize strategies for determining the boundary conditions needed to characterize the full range of operating conditions of phased-array transducers, including beam steering, high output levels, and challenging geometries of clinical interest.
The third aim seeks to use measurement and simulation tools to quantify how tissue inhomogeneities distort an incident ultrasound beam, including the development of indices that capture the impacts of readily identified geometrical features on 3D ultrasound fields ? e.g., orientation and curvature of the skin surface, uniformity of transcutaneous fat, and rib location. Overall, this effort will impact public health by providing a basis for improved treatment planning capabilities in FUS applications.

Public Health Relevance

Focused ultrasound surgery (FUS) is a rapidly developing field in which focused beams of ultrasound are delivered to remote treatment sites such as tumors inside a patient's body. To realize the potential of this technology for clinical applications, it is necessary to know the ultrasound fields to which patients are exposed. The proposed work will advance techniques for accurately characterizing the ultrasound fields generated in tissue to help ensure that clinical FUS therapies remain safe and effective.

National Institute of Health (NIH)
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Research Project (R01)
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Biomedical Imaging Technology Study Section (BMIT)
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King, Randy Lee
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University of Washington
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United States
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Ghanem, Mohamed A; Maxwell, Adam D; Kreider, Wayne et al. (2018) Field Characterization and Compensation of Vibrational Nonuniformity for a 256-Element Focused Ultrasound Phased Array. IEEE Trans Ultrason Ferroelectr Freq Control 65:1618-1630