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Open Access Publications from the University of California

Fine Needle Elastography (FNE) for biomechanically determining needle insertion forces and quantitative assessment of intranodular heterogeneity in tissue mechanical properties

  • Author(s): Wickramaratne, Dayan Jayasanka
  • Advisor(s): Gimzewski, James K
  • Schmidt, Jacob J
  • et al.

Diseased tissues exhibit changes in mechanical properties and thus possess clinical diagnostic significance. This dissertation focuses mainly on thyroid nodules that are commonly found in about 19-67% of the population and 5-10% of which are carcinoma. Currently the primary method of thyroid nodule diagnosis - Fine Needle Aspiration Cytology (FNAC). FNAC has much room for improvement of diagnostic accuracy due to 15-32% nondiagnostic results and 20-30% indeterminate (suspicious) reports that lead for many complications for the patients. Furthermore, there is a wealth of variation of mechanical properties unique to different kinds of thyroid malignancies that are inaccessible with other existing methodologies. This dissertation introduces the novel concept of Fine Needle Elastography (FNE) and presents the design and development of a FNE Device prototype integrated with a FNAC needle that allows for quantitative and sensitive assessment of tissues and materials based on local variations in elastic, friction, and cutting forces on needle insertion. A piezoelectric force-sensor at the base of FNA needle measures the forces opposing needle penetration with the micrometer-scale resolution. The axial resolution (~20μm) of FNE device was tested using control mm size gelatin matrices and unripe pear in assessing needle penetration resistance, force heterogeneity and optimization of needle penetration velocity. Further, it is demonstrated the usefulness of FNE in quantitative, biomechanical differentiation of simulated thyroid tumor nodules in an ultrasound neck phantom. Fluid or solid nodules were probed in the phantom study coupled with real-time ultrasound guidance. The preliminary FNE data shows significantly higher force and stiffness variations (1-D Force Heterogeneity; HF,a=6.5mN, HF,q=8.25mN and Stiffness Heterogeneity; HS,a=0.0274kN/m, HS,q=0.0395kN/m) in solid nodules compared either to fluid nodules or to regions corresponding to simulated healthy thyroid tissue within the ultrasound phantom. Further investigation of the utility of the device in a proper clinical setting with excised thyroid tissue and in vivo testing of human subjects with different kinds of thyroid carcinoma can be used to develop a database of FNE data relating to each kind of thyroid nodule. The preliminary results suggest future applications of the FNE Device for in vivo FNE biopsies based on force and stiffness heterogeneity to diagnose thyroid nodules as an ancillary diagnostic tool in thyroid cancer management. FNE methodology could be potentially extended to diagnosis and management of other percutaneous diagnosis methodologies in diagnosing breast cancer, liver cancer etc.

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