Virtual Extended-Range Tomography (VERT): Contact-free realistic ultrasonic bone imaging

TL;DR

VERT introduces a contact-free ultrasonic imaging method that enhances resolution and robustness in high-contrast, extended-range bone imaging, overcoming access and contrast challenges without prior interior knowledge.

Contribution

The paper presents VERT, a novel approach that places virtual transducers on the ROI to improve ultrasonic tomography resolution and robustness in challenging high-contrast, extended-range scenarios.

Findings

VERT outperforms traditional BRT in resolution and robustness.

VERT maintains or improves speed compared to BRT.

Approaching the resolution limit of direct ROI BRT.

Abstract

Ultrasound tomography generally struggles to reconstruct high-contrast and/or extended-range problems. A prime example is site-specific in-vivo bone imaging, crucial for accurately assessing the risk of life-threatening fractures, which are preventable given accurate diagnosis and treatment. In this type of problem, two main obstacles arise: (a) an external region prohibits access to the region of interest (ROI), and (b) high contrast exists between the two regions. These challenges impede existing algorithms -- including bent-ray tomography (BRT), known for its robustness, speed, and reasonable short-range resolution. We propose Virtual Extended-Range Tomography (VERT), which tackles these challenges through (a) placement of virtual transducers directly on the ROI, facilitating (b) rapid initialisation before BRT inversion. In-silico validation against BRT with and without a-priori information shows superior resolution and robustness -- while maintaining or even improving speed. These improvements are drastic where the external region is much larger than the ROI. Additional validation against the practically impossible -- BRT directly on the ROI -- demonstrates that VERT is approaching the resolution limit. The capability to solve high-contrast extended-range tomography problems without prior knowledge about the ROI's interior has many implications. VERT has the potential to unlock site-specific in-vivo bone imaging for assessing fracture risk, potentially saving millions of lives globally. In other applications, VERT may replace classical BRT to yield improvements in resolution, robustness and speed -- especially where the ROI does not cover the entire imaging array. For even higher resolution, VERT offers a reliable starting background to complement algorithms with less robustness and high computational costs.