Blood flow measurements with ultrasound
Background and principle of Multiphysics simulations
Ultrasound imaging remains the cornerstone of cardiovascular medicine, with blood flow imaging one of the most important on-board modalities of clinical scanners. Traditional and still widely used modalities are (pulsed) Doppler imaging, measuring the velocity in a sample volume or along the scan line, and colour flow imaging, displaying colour-coded flow velocities within the imaging plane. Important drawbacks of these modalities is that only the velocity component in the direction of the ultrasound beam is being detected. This is not so much of a problem in conditions with well aligned flows and with an acoustic window that permits to sufficiently align the beam with the flow direction, but does become problematic in complex flows that may be intrinsically 3D and with regions of high as well as low flow velocities, such as flow in the carotid artery and its bifurcation, or intracardiac flows. The medical ultrasound community is almost permanently searching for better and new ways to transmit and receive ultrasound signals and algorithms for post-processing of our data.
Our research group, with its expertise in computational fluid dynamics, teamed up with the ultrasound group of profs. Hans Torp and Lasse Løvstakken at the NTNU in Trondheim, Norway and developed a methodology that allows us to transform 3D flow simulations (both computational fluid dynamics (CFD) or fluid-structure interaction simulations (FSI) with moving boundaries) into synthetic ultrasound data. To do this, we use velocity information from the simulations to move seeded ultrasound scatters in time and space. The interaction of these scatterers with an imposed ultrasound field is calculated using the Field II software. This workflow set the basis for the joint PhD of Dr. Abigail Swillens and is illustrated in the video below.
Applications
In her PhD thesis, Abigail Swillens mainly focussed on blood flow in the carotid bifurcation, exploring vector Doppler and speckle tracking as techniques that would allow for more accurate multidimensional flow and assessing the accuracy of shear rate estimations [1-4]. The same principle was applied to complex forearm blood flow following vascular access creation [5], blood flow measurement in the mouse [6] and to a CFD model of the neonatal [7] (results shown below) and adult left heart [8].
The synthetic datasets also served as reference in a paper on a novel method to reconstruct the flow field from 2D ultrasound flow velocity measurements [9].
References
- Swillens A, Løvstakken L, Kips J, Torp H and Segers P. Ultrasound simulation of complex flow velocity fields based on computational fluid dynamics. IEEE Trans Ultrason Ferroelectr Freq Control. 2009;56:546-56.
- Swillens A, Degroote J, Vierendeels J, Lovstakken L and Segers P. A simulation environment for validating ultrasonic blood flow and vessel wall imaging based on fluid-structure interaction simulations: ultrasonic assessment of arterial distension and wall shear rate. Med Phys. 2010;37:4318-30.
- Swillens A, Segers P and Lovstakken L. Two-dimensional flow imaging in the carotid bifurcation using a combined speckle tracking and phase-shift estimator: a study based on ultrasound simulations and in vivo analysis. Ultrasound Med Biol. 2010;36:1722-35.
- Swillens A, Segers P, Torp H and Løvstakken L. Two-dimensional blood velocity estimation with ultrasound: speckle tracking versus crossed-beam vector Doppler based on flow simulations in a carotid bifurcation model. IEEE Trans Ultrason Ferroelectr Freq Control. 2010;57:327-39.
- Van Canneyt K, Swillens A, Lovstakken L, Antiga L, Verdonck P and Segers P. The accuracy of ultrasound volume flow measurements in the complex flow setting of a forearm vascular access. J Vasc Access. 2013;14:281-90.
- Swillens A, Shcherbakova D, Trachet B and Segers P. Pitfalls of Doppler Measurements for Arterial Blood Flow Quantification in Small Animal Research: A Study Based on Virtual Ultrasound Imaging. Ultrasound Med Biol. 2016;42:1399-411.
- Van Cauwenberge J, Lovstakken L, Fadnes S, Rodriguez-Morales A, Vierendeels J, Segers P and Swillens A. Assessing the Performance of Ultrafast Vector Flow Imaging in the Neonatal Heart via Multiphysics Modeling and In Vitro Experiments. IEEE Trans Ultrason Ferroelectr Freq Control. 2016;63:1772-1785.
- Londono-Hoyos FJ, Swillens A, Van Cauwenberge J, Meyers B, Koppula MR, Vlachos P, Chirinos JA and Segers P. Assessment of methodologies to calculate intraventricular pressure differences in computational models and patients. Med Biol Eng Comput. 2018;56:469-481.
- Meyers BA, Goergen CJ, Segers P and Vlachos PP. Colour-Doppler echocardiography flow field velocity reconstruction using a streamfunction-vorticity formulation. J R Soc Interface. 2020;17:20200741.
IBiTech researchers currently active on the project
Patrick Segers (contact)
