Complex shear modulus reconstruction using ultrasound shear-wave imaging

Doppler;Ultrasound;Shear wave imaging;Finite difference time domain (FDTD)

Orescanin, Marko

关键词: Doppler;    Ultrasound;    Shear wave imaging;    Finite difference time domain (FDTD);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/18401/Orescanin_Marko.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Many pathological processes in tissues are recognized by morphological changesthat reflect alterations of the soft tissue mechanical properties. Ultrasoundshear-wave imaging can provide quantitative information about soft tissuemechanical properties, specifically the complex shear modulus. Advancingthis field has the potential to bridge molecular, cellular, and tissue biologyand to influence medical diagnoses and patient treatment. This dissertationdescribes several quantitative developments in the field of ultrasoundshear-wave imaging. The initial study is a time-domain method for quantitativereconstruction of the complex shear modulus, estimated from thetracked displacement of the embedded spherical scatterer. This study alsoestablished a methodology for independent experimental verification of estimatedmaterial properties using rheometer measurements. The second studypresents a technique for shear-wave imaging using a vibrating needle sourcefor shear wave excitation. An advantage of such an approach is extendedbandwidth of the measurement and a well-defined shear wave propagationthat can be advantageous in the complex shear modulus reconstruction. Thismethod was used to explore viscoelastic mechanisms in liver tissue and toexplore different modeling approaches. It was found that the shear dynamicviscosity provides more contrast in imaging thermal damage in porcine liver,as compared to the shear elastic modulus. The third study was to developan FDTD 3D viscoelastic solver capable of accurate modeling of shear wavepropagation in heterogeneous media. Numerical results are experimentallyvalidated. Furthermore, this numerical framework is used to study complexmodulus imaging, specifically a direct algebraic Helmholtz inversion.The practical limitations and complex shear modulus reconstruction artifactswere studied, where it was found that distortions can be minimizedsimply by imaging the magnitude of the complex shear modulus. The finalstudy was a recursive Bayesian solution to complex shear modulus reconstruction. A result of this is a stochastic filtering approach that uses a priori information about spatio-temporal dynamics of wave propagation to providelow variance estimates of the complex shear modulus. The stochastic filteringapproach is studied both in simulation and experiments. The benefit of such an approach is low variance online reconstruction of the complex shear modulus per imaging frequency.