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UBC Theses and Dissertations

Towards liver shear wave vibro-elastography : method repeatability and image registration technique Hemily, Julie


Liver fibrosis is a largely prevalent concern in Canada and world-wide, due to high rates of Hepatitis, fatty liver disease, alcoholism, as well as several other possible causes. It is currently diagnosed and staged by performing biopsies or by tissue elasticity measurements referred to as elastography. Elastography methods are a relatively new means of measuring the mechanical properties of soft tissue non-invasively by measuring and processing the propagation of shear waves through the body. The Robotics and Control Laboratory at the University of British Columbia has developed an elastography technique, Vibro-elastography, that can quantitatively measure soft tissue stiffness in real time. It has previously been applied to prostate and breast pathologies. It is now being developed and optimized for liver applications. To validate Vibro-elastography as a new diagnostic tool, a comparison study should be performed on a clinical population. This work sets out to lay out the prerequisites needed to implement a full clinical study. It starts out with a repeatability study using a tissue phantom to ensure repeatable results and compare our results to manufacturer stiffness values. In this work, we compare the precision of several different implementations of Vibro-elastography including the placement of the excitation source, data acquisition techniques and single versus multi-frequency excitation. Most of the implementations resulted in good, repeatable results, regardless of exciter placement. The quality of wave propagation deteriorated with depth as expected, but elasticity results remained repeatable even at deeper regions of interest. The parameters are selected and designed for the use on the liver. Finally, a registration pipeline and initial case trial has been presented as a suggested means of comparing the elastography data obtained using Vibro-elastography and any elastography measures that can be obtained from a magnetic resonance system. Using manual fiducial vessel markers and applying an Iterative Closest Point registration process results in a quick alignment of the ultrasound and MRI volumes with registration error less than 20 mm.

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