Pressure Gradient Estimation

Research output: Book/ReportPh.D. thesis

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Abstract

Atherosclerosis development can lead to stroke, which is one of the most common causes of death. Different techniques exist to assess the severity of atherosclerosis. These techniques depend on the region of interest. In the coronary arteries, pressure gradients are often measured using pressure-sensitive catheters, whereas, in the carotid arteries, the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and The European Carotid Surgery Trial (ECST) have been used to measure stenosis percentage. These methods are invasive, expensive, and not without risk. In this project, it is hypothesized that non-invasive, precise, and accurate pressure differences can be estimated using synthetic aperture ultrasound with a precision better than invasive catheters. Here, pressure differences can be used for analyzing the blood flow along a streamline, where high gradients indicate stenotic development. Data are acquired using linear transducers in combination with the Vantage 256 research scanner and pressure differences are estimated from the unsteady Bernoulli equation, which requires precise calculations of blood velocity and acceleration. Here, transverse oscillation provides the flow angle, and directional cross-correlation is used for precise estimations of velocity and acceleration. The method is evaluated on simulations and phantom measurements, compared to pressure catheters, and applied to ten healthy volunteers. The result of the simulation shows that the estimated pressure differences follow the same trend as the simulated pressure difference with mean absolute errors (MAE) of 2.41 Pa. The estimated peak negative pressure difference shows an underestimation of 16.2% when compared to the true simulated pressure difference. The estimator is also compared to pressure catheters in a phantom setup, and it is seen that the best precision is achieved with the ultrasound approach, which detected small pressure differences ranging from a maximum positive pressure difference of 3.56 Pa to a maximum negative pressure difference of -82.56 Pa, with a coefficient of variation of 6.98% (6.01 Pa). The pressure catheters estimate pressure differences ranging from a maximum positive pressure difference of 1.98 Pa to a maximum negative pressure difference of -103 Pa, with a coefficient of variation of 11% (11.56 Pa). The results from the in-vivo experiment show an average precision of pressure differences across ten healthy volunteers of 11.19% (31.47 Pa). This shows that non-invasive precise pressure differences can be estimated in a realistic clinical setup. The ultrasound method is risk-free, allows for repeated measurements, and can achieve pressure differences without the complications otherwise associated with invasive catheters.
Original languageEnglish
PublisherDTU Health Technology
Number of pages146
Publication statusPublished - 2024

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