Advances in Elastography Using Geometrically Focused Actuation
Kearney, Steven P.
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Palpation, a diagnostic method based on changes in tissue characteristics, is a common point of care examination. These changes are a result of pathological changes in tissue mechanical properties, and elastography quantifies these changes for clinical diagnosis. This dissertation has advanced several applications of elastography, and these include: in vivo skin optical elastography (OE), in vivo mouse brain sample interval modulation (SLIM) magnetic resonance elastography (MRE), ex vivo prostate MRE, and in situ Lung MRE. The novel method of geometrically focused actuation (GFA) has been included in all of the applications, when possible. GFA has the advantage of wide bandwidth actuation capabilities. For skin elastography, the aim was to develop a novel in vivo skin surface wave actuator to be used for wideband optical elastography, and to investigate the applicability of various viscoelastic models of human skin. It was found that 2 particular models stood out. In terms of variability, the fractional order models performed the best with coefficients of variation as low as 15%. In quality of fit, the SLS model outperformed all others with a R2 of 0.93. For mouse brain MRE, the aim was to further the development of SLIM-MRE (simultaneous motion encoding of the 3D wave field) using a novel phase varying method and the original phase constant method. Both SLIM methods showed good agreement with the conventional MRE method. SLIM-PC, compares to conventional with less error in terms of the shear modulus maps than SLIM-PV, but requires an increase in TE. For prostate MRE, the aim was to investigate the efficacy of ex vivo prostate MRE, and test a threshold based cancer identification method. The threshold based determination of positive and negative prostate cancer segments resulted in a sensitivity (specificity) of 85.7% (53.7%). For lung MRE, the aim was to investigate the potential application of UHF proton in vivo lung MRE. It was found that proton lung MRE at 9.4 T does not provide enough signal to perform in vivo experiments.
Magnetic Resonance Elastography
Mouse Brain MRE