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Echocardiography is the most commonly used image modality in cardiology, assessing several aspects of cardiac
viability. The importance of cardiac hemodynamics and 4D blood flow motion has recently been highlighted, however
such assessment is still difficult using routine echo-imaging. Instead, combining imaging with computational fluid
dynamics (CFD)-simulations has proven valuable, but only a few models have been applied clinically. In the following,
patient-specific CFD-simulations from transthoracic dobutamin stress echocardiography have been used to analyze the
left ventricular 4D blood flow in three subjects: two with normal and one with reduced left ventricular function. At each
stress level, 4D-images were acquired using a GE Vivid E9 (4VD, 1.7MHz/3.3MHz) and velocity fields simulated using
a presented pathway involving endocardial segmentation, valve position identification, and solution of the
incompressible Navier-Stokes equation. Flow components defined as direct flow, delayed ejection flow, retained inflow,
and residual volume were calculated by particle tracing using 4th-order Runge-Kutta integration. Additionally, systolic
and diastolic average velocity fields were generated. Results indicated no major changes in average velocity fields for
any of the subjects. For the two subjects with normal left ventricular function, increased direct flow, decreased delayed
ejection flow, constant retained inflow, and a considerable drop in residual volume was seen at increasing stress.
Contrary, for the subject with reduced left ventricular function, the delayed ejection flow increased whilst the retained
inflow decreased at increasing stress levels. This feasibility study represents one of the first clinical applications of an
echo-based patient-specific CFD-model at elevated stress levels, and highlights the potential of using echo-based models
to capture highly transient flow events, as well as the ability of using simulation tools to study clinically complex
phenomena. With larger patient studies planned for the future, and with the possibility of adding more anatomical
features into the model framework, the current work demonstrates the potential of patient-specific CFD-models as a tool
for quantifying 4D blood flow in the heart.
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