Ph.D Thesis | |

Ph.D Student | Burstein Pablo |
---|---|

Subject | A Method of 3D Reconstruction of Flow Velocity Fields from Color-Doppler Ultrasound |

Department | Department of Biomedical Engineering |

Supervisor | PROFESSOR EMERITUS Dan Adam |

An integral automatic and self-contained solution to
the problem of reconstructing the flow velocity field from standard Color
Doppler Ultrasound (CDUS) images is presented. This includes other sub-tasks
such as lumen boundary extraction, vessel geometry modeling, low-flow
extrapolation, and angle correction. CDUS images are acquired using standard,
hand-held transducers, with no restrictions on the choice of transducer
position and orientation. A modified balloon algorithm is used for edge
extraction, providing a mean radius error of 3.45%, compared to the 7.01%
obtained by estimating the boundary from the color maps. The color-maps are,
therefore, used for obtaining the initial guess which greatly reduces the
search area (and processing time), and provides an automatic way for
initializing the balloon algorithm close to the lumen boundary, and obtaining
good estimates of the parameters governing the balloon evolution. The
3D-velocity flow field is reconstructed by means of a physical model of flow.
The Navier-Stokes and Continuity equations are solved using Penalty Function
Approach*-*Finite Elements* *Method* *(PFA-FEM). The
penalty parameter regularizes the solution. We studied the effects on the
reconstructed flow field of measurement noise, wall-motion filtering and poor
geometry estimation. It is noticed that poor geometry estimation affects the
flow field reconstruction more than measurement noise and wall motion
filtering, but it is easily corrected by better spatial acquisition protocols.
Measurement noise effects are corrected by means of the PFA-FEM, while the
wall-motion filtering distortions are dealt with by prior parabolic
extrapolation. Feasibility of the method is shown, using a simulated flow field
and CDUS images acquired from a phantom. Even though the velocity measurements,
used as boundary conditions, are highly distorted, the reconstruction error,
MSE = 0.05, is two orders of magnitude smaller than the error at the
inlet and outlet planes (boundary conditions), MSE = 4.92.