High-Volume-Rate Ultrasound for Quantitative Assessments of Vascular Function

Abstract

Free flap surgery is a common reconstructive technique to repair tissue damage after trauma or cancer removal. This complex procedure involves the transfer of tissue, along with its associated blood supply, from one part of the body to another. While these surgeries have high overall success rates, the risk of vascular complications remains a concern. Thus, rigorous post-operative vascular monitoring of free flaps is required for the early detection and intervention of complications to prevent tissue necrosis or complete flap failure. Despite the critical importance of vascular monitoring, clinicians do not currently have an objective measurement tool that can quantify the volume of blood perfusing the flap. Instead, they rely on tools which indicate the presence or absence of blood flow (e.g. Doppler pens) coupled with visual inspection of the flap. As a result, vascular compromise can go unnoticed for several hours which increases the risk of partial or total flap failure.

Ultrasound imaging is a potential solution to the vascular monitoring of free flaps given its ability to accurately measure blood flow velocities at the bedside. However, the accurate quantification of blood flow volumes requires the use of high-volume-rate 3D ultrasound imaging which generally lacks bedside applicability due to the large size of the associated processing electronics. The goal of this thesis is to investigate novel solutions which enable the acquisition of accurate 3D flow measurements with portable ultrasound systems. Specifically, this work has two primary focal points: 1) the investigation and validation of data reduction strategies for 3D ultrasound to facilitate the use of portable processing systems, and 2) the enhancement of high-rate ultrasound flow estimation accuracy to optimize the performance of volumetric blood flow measurements. At the end of this work, the first in vivo volumetric blood flow measurement with a portable 3D ultrasound system is showcased.

Overall, this thesis presents several advances on the state-of-the-art of 3D ultrasound flow imaging technology. The capabilities of small-scale 3D ultrasound technology are demonstrated indicating a positive outlook for future clinical applications. Indeed, the core focus of this work on accurate blood flow quantification is to ensure that clinicians have access to reliable, quantitative data enabling them to make objective decisions on patient care. In the case of free flap vascular monitoring, 3D ultrasound has the potential to significantly improve the early detection of vascular complications which could mitigate the need for additional surgeries and reduce the rates of partial and total flap failures.