Two-step hybrid virtual array ray (VAR) technique for focusing through the rib cage

Area of Science:

• Medical physics
• Biomedical engineering
• Acoustic imaging

Background:

• High intensity focused ultrasound (HIFU) is a promising noninvasive treatment modality.
• Rib cage structures can obstruct ultrasound beams, limiting therapeutic applications like liver tumor treatment.
• Phased array applicators are crucial for precise ultrasound focusing.

Purpose of the Study:

• To develop and investigate a new methodology for noninvasively focusing ultrasonic beams in the presence of the rib cage.
• To enable effective HIFU treatment for liver tumors partially shadowed by rib obstacles.
• To facilitate efficient ultrasound computational analysis and pattern synthesis within the rib cage interior.

Main Methods:

• Introduction of a virtual array along intercostal spacings to generate prespecified intensity levels at control points.
• Design of an actual feed array to induce virtual sources between intercostal spacings.
• Optimization using pseudo-inverse technique (minimum norm least squares) and a constrained preconditioned pseudo-inverse method.

Main Results:

• The proposed technique successfully calculates required primary sources for the feed array.
• Minimal power deposition over solid obstacles (ribs) is maintained during the process.
• The methodology allows for effective ultrasound beam focusing despite rib cage interference.

Conclusions:

• The developed methodology provides a viable solution for noninvasive ultrasound focusing through the rib cage.
• This approach enhances the applicability of HIFU for treating abdominal tumors obscured by the ribs.
• The technique ensures safety by minimizing unintended energy deposition on bone structures.