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This study introduces a new semidefinite relaxation (SDR) refocusing method to improve high-intensity focused ultrasound (HIFU) therapy for tumors near ribs. The approach enhances power delivery to targets while minimizing rib exposure and potential damage.

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Three-Dimensional Phase Resolved Functional Lung Magnetic Resonance Imaging

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Published on: June 21, 2024

Area of Science:

Medical Physics
Biomedical Engineering
Acoustic Imaging

Background:

High-intensity focused ultrasound (HIFU) therapy faces challenges with tumors near the rib cage due to beam distortion.
Ribs can cause significant acoustic aberration, reducing focusing gain and potentially causing collateral damage like skin burns during hepatic tumor ablation.

Purpose of the Study:

To develop and evaluate a novel refocusing algorithm for HIFU that optimizes power delivery to the target while controlling energy deposition on overlying ribs.
To address limitations of previous algorithms that did not allow for controlled transmission through ribs.

Main Methods:

A semidefinite relaxation (SDR) technique was employed to approximate the non-convex optimization problem for HIFU refocusing.
A finite-difference time-domain (FDTD) model simulated acoustic propagation through inhomogeneous tissues, including ribs.
Temperature simulations utilized the transient bioheat transfer equation (tBHTE) to assess treatment efficacy.

Main Results:

The SDR-based method, termed limited power deposition (LPD), demonstrated improved focusing gain compared to previous methods.
The LPD approach effectively controlled side lobes and allowed for specifying acceptable rib exposure levels.
Simulations confirmed that the LPD method generates realizable array excitation vectors compatible with existing drivers.

Conclusions:

The novel SDR refocusing approach offers a more efficient way to steer HIFU power towards targets obscured by ribs.
This method enhances therapeutic efficacy by improving focusing gain and minimizing collateral damage to ribs and surrounding tissues.
The LPD method shows promise for safer and more effective HIFU treatments in challenging anatomical locations.