Synthetic Aperture Vector Flow Imaging

The main objective of this project was to continue the development of a synthetic aperture vector flow estimator. This type of estimator is capable of overcoming two of the major limitations in conventional ultrasound systems: 1) the inability to scan large region of interest with high temporal resolutions; 2) the lack of capability in detecting flow other than the one along the direction of the beam. Addressing these technical limitations would translate in the clinic as a gain in valuable clinical information and a removal of operator-dependant sources of error, which would improve the diagnosis. The main contribution of this work was the development of an angle estimator which features high accuracy and low standard deviation over the full 360◦ range. The estimator demonstrated its capability of operating at high frame rates (> 1000 Hz), and simultaneously detecting a large range of flow velocities (0.05 – 3 m s−1 ). The estimator was also extended to a variety of geometries without major modifications, including a 2-D matrix array for full 3-D velocity estimation. Furthermore, a developed novel energy based tissue echo-canceler provided a new effective perspective for removing the tissue signal, specially when the tissue and flow spectra overlaps. The approach was investigated with a series of flow simulations that included vessel wall movement, and demonstrated its capability of diminish the effects of a moving vessel wall in both simulations and in vivo measurements. Finally, this thesis showed that novel information can be obtained with vector velocity methods providing quantitative estimates of blood flow and insight into the complexity of the hemodynamics dynamics. This could give the clinician a new tool in assessment and treatment of a broad range of diseases.