A Tracking prior to Localization workflow for Ultrasound Localization Microscopy

TL;DR

This paper introduces a novel Tracking-and-Localization (TAL) workflow for Ultrasound Localization Microscopy that improves microbubble tracking accuracy and reduces acquisition times compared to traditional methods, especially at higher concentrations.

Contribution

The study proposes reversing the conventional Localization-and-Tracking workflow to a Tracking-and-Localization approach, demonstrating superior performance through extensive benchmarking.

Findings

TAL outperforms LAT in angiography and velocity mapping.

TAL provides more accurate velocity measurements during cardiac cycles.

The method reduces acquisition times and improves robustness at high microbubble concentrations.

Abstract

Ultrasound Localization Microscopy (ULM) has proven effective in resolving microvascular structures and local mean velocities at sub-diffraction-limited scales, offering high-resolution imaging capabilities. Dynamic ULM (DULM) enables the creation of angiography or velocity movies throughout cardiac cycles. Currently, these techniques rely on a Localization-and-Tracking (LAT) workflow consisting in detecting microbubbles (MB) in the frames before pairing them to generate tracks. While conventional LAT methods perform well at low concentrations, they suffer from longer acquisition times and degraded localization and tracking accuracy at higher concentrations, leading to biased angiogram reconstruction and velocity estimation. In this study, we propose a novel approach to address these challenges by reversing the current workflow. The proposed method, Tracking-and-Localization (TAL), relies on first tracking the MB and then performing localization. Through comprehensive benchmarking using both in silico and in vivo experiments and employing various metrics to quantify ULM angiography and velocity maps, we demonstrate that the TAL method consistently outperforms the reference LAT workflow. Moreover, when applied to DULM, TAL successfully extracts velocity variations along the cardiac cycle with improved repeatability. The findings of this work highlight the effectiveness of the TAL approach in overcoming the limitations of conventional LAT methods, providing enhanced ULM angiography and velocity imaging.