Implementation and Assessment of Supersonic Shear Imaging Techniques

Shear Wave Elastography (SWE) is an ultrasound modality which can measure tissue elasticity quantitatively. It provides valuable diagnostic information in addition to conventional ultrasound modalities. SWE has been shown to provide improved performance for detection and classification of several diseases, such as breast and prostate cancer. Tissue elasticity is also a valuable diagnostic property for diffuse diseases that don't have any visible structural anomalies, such as fibrosis. This project aimed to implement state-of-the-art in Supersonic Shear Imaging (SSI) on a Verasonics ultrasound research system, and to assess the performance of the elasticity estimation on various tissue-mimicking phantoms. A setup was developed with a linear array transducer to excite shear waves in tissue using acoustic radiation force, the propagation of the waves were imaged using plane wave ultrafast ultrasound and the tissue elasticity was estimated as a function of the shear wave velocity. A few different approaches to the velocity estimation were implemented and discussed, an algorithm based on line detection was found to be fast, but with poor resolution. While a method using cross-correlations to estimate propagation provided better velocity maps, but was considerably slower. With either approach it is found that careful choice of estimation parameters is necessary to provide good performance in terms of accuracy and efficiency. The implementation was able detect a soft cyst in a heterogeneous phantom despite irregularities in the surrounding medium. Elastic cysts were also detected in a multi-purpose phantom, with far better contrast than the B-mode equivalent. Finally, a setup using two ultrasound transducers was implemented, using one transducer to generate shear waves and the other for imaging