Optimization of transcostal phased-array refocusing using sparse semidefinite relaxation method | JoVE Visualize

Area of Science:

Medical Physics
Biomedical Engineering
Acoustic Imaging

Background:

Rib shadowing significantly impedes high-intensity focused ultrasound (HIFU) tumor treatment by absorbing energy and distorting beams.
Current methods struggle to achieve effective heat deposition in target regions obscured by bone structures.
Developing advanced focusing strategies is crucial for overcoming these limitations in HIFU therapy.

Purpose of the Study:

To introduce a new sparsity-inducing optimization method for HIFU focusing, specifically addressing challenges posed by rib shadowing.
To reduce total power deposition on the region of interest (ROI) by strategically removing transducer elements.
To demonstrate the efficacy of this novel approach compared to traditional shadowing models.

Main Methods:

The study builds upon the limited power deposition (LPD) method, incorporating semidefinite relaxation (SDR) to handle non-convex constraints.
A novel sparsity-inducing technique utilizing the one-norm squared is introduced to optimize transducer element activation.
Wave propagation was modeled using a finite-difference time domain (FDTD) model, and temperature distributions were simulated using the inhomogeneous bioheat transfer equation (BHTE).

Main Results:

The induced sparsity LPD method demonstrated improved heat deposition in the target region compared to the ray tracing (shadowing) approach.
Simulations showed the effectiveness of the sparsity-inducing technique in overcoming energy absorption and beam distortion caused by ribs.
The method successfully focused a 1-MHz spherical phased array on a target within an inhomogeneous medium.

Conclusions:

Optimization-based sparsity-inducing techniques offer significant advantages over traditional shadowing approaches for HIFU treatments near ribs.
The proposed method enhances therapeutic efficacy by improving targeted heat deposition and minimizing unwanted energy absorption.
This approach represents a promising advancement for overcoming anatomical barriers in focused ultrasound therapy.