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UBC Theses and Dissertations

3D ultrafast ultrasound elastography Hashemi, Hoda Sadat


Ultrasound elastography is a medical imaging technique that quantifies tissue mechanical properties such as elasticity. It involves applying a force to the tissue, and measuring the resulting deformations to calculate tissue elasticity by solving an inverse problem. 3D imaging provides more spatial information on tissue deformation compared to conventional 2D frames. However, 3D imaging has several bottlenecks that limit its practicality in clinical settings, including a long data acquisition time that can introduce artifacts from patient or sonographer motion and a low frame rate that limits the applied force’s frequency range by the Nyquist frequency. A wider frequency range can enable a more comprehensive tissue modeling and characterization. Furthermore, most ultrasound elastography techniques measure displacement only in one axial direction, but it is important to consider that any force applied to the tissue leads to 3D tissue deformation due to tissue incompressibility. Therefore, it is crucial to explore new approaches to overcome these limitations and fully utilize the potential of 3D imaging in clinical applications. Shear wave absolute vibro-elastography (S-WAVE) is an elastography technique where an external vibration source generates steady-state mechanical vibrations inside the tissue. This thesis presents two novel techniques for high-frame-rate S-WAVE volumetric data acquisition as well as the algorithms to calculate elasticity volumes. The standard quasi-real-time technique using a wobbler transducer involves sweeping the transducer mechanically and acquiring 2D images at each location. The images are then reconstructed into a 3D volume which takes less than 2 s to collect 100 data volumes. Alternatively, using a matrix array transducer, we introduce the first S-WAVE method with real-time volumetric data acquisition which takes 0.05 s to collect 100 data volumes. We propose a novel method for estimating axial, lateral, and elevational displacements which in turn enables the use of the curl of the displacements in the elasticity reconstruction to reduce artifacts. By employing high volume rates, we extend the range of S-WAVE excitation to 800 Hz. The proposed method is validated using homogeneous and heterogeneous phantoms and in ex vivo bovine liver studies.

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