Retrieving pulsatility in ultrasound localization microscopy

Master thesis (2022)

Authors

M.S.J. Wiersma Mechanical Engineering

Contributors

B.G. Heiles ImPhys/Medical Imaging - AS (supervisor 1)
D. Kalisvaart Team Carlas Smith - Mechanical, Maritime and Materials Engineering (supervisor 1)
D. Maresca ImPhys/Medical Imaging - AS (supervisor 1)
C.S. Smith Team Carlas Smith - Mechanical, Maritime and Materials Engineering (supervisor 1)
Raf Van de Plas Team Raf Van de Plas - Mechanical, Maritime and Materials Engineering (supervisor 2)
G.J. Verbiest Dynamics of Micro and Nano Systems - Mechanical, Maritime and Materials Engineering (supervisor 2)
Faculty
Mechanical Engineering
Copyright: © 2022 Myrthe Wiersma
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Published Date

20-05-2022

Language

English

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Faculty

Mechanical Engineering

Abstract

Ultrafast ultrasound localization microscopy (ULM) is a super-resolved vascular imaging method that provides a 10-fold improvement in resolution compared to ultrafast ultrasound Doppler imaging. Because typical ULM acquisitions accumulate large numbers of synthetic microbubble (MB) tracks over hundreds of cardiac cycles, transient hemodynamic variations such as pulsatility get averaged out. Here we introduce two independent processing methods to retrieve pulsatile flow information from MB tracks sampled at kilohertz framerates and demonstrate their potential on a simulated dataset. Our first approach filters out ULM localization grid artifacts and successfully recovers the pulsatility fraction Pf with a root mean square error of 3.3%. Our second approach relies on the derivation of the velocity distribution of MBs as observed from a stationary observer. We show that pulsatile flow gives rise to a bimodal velocity distribution with peaks indicating the maximum and minimum velocity of the cardiac cycle. Measuring the locations of these peaks, we successfully estimated Pf with an error of 5.2%. Last, we evaluated the impact of the MB localization precision σ on our ability to retrieve the bimodal signature of a pulsatile flow. Together, our results demonstrate that pulsatility can be retrieved from high framerate ULM acquisitions and that the estimation of the pulsatility fraction improves with MB localization precision.