Towards a molecular level understanding of elasticity in tissues and hydrogels

Mallika Sridhar, Jie Liu, Michael F. Insana

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In elasticity imaging, tissues are stimulated with mechanical forces while spatiotemporal strain responses are observed. The basis for diagnostic imaging is that disease processes characteristically alter the structure of connective tissues that determine viscoelastic properties. Time-varying strains for steplike stress stimuli were measured in gelatin hydrogels and normal breast tissue. The medium's mechanical response function - the retardance-time spectrum - was computed. This spectrum is the continuous distribution of time constants that characterizes viscoelastic behavior. Spectra were parameterized using low order discrete rheological models from linear viscoelastic theory to reduce data dimensionality yielding parameters related to stiffness and viscosity: elastic strain and two retardation time constants. Broadband, continuous, bi-modal spectra was obtained for gelatin samples. Similar spectra with narrow bandwidth were found for breast tissue. Both characteristic of lightly cross-linked amorphous polymers. Measured time constants in gelatin indicated fast (1-10 s) fluidic behavior and a slower (50-400 s) matrix restructuring. Corresponding parameters in breast were 3.2±0.8 s and 42.0±28 s. Phantom imaging studies showed that these parameters provided consistently high target contrast. Although the ultra-structure of collagen within gelatin and breast stroma is different, their mechanical behavior is quite similar. Creep in both media are consistent with the molecular theory of entanglement coupling proposed to explain amorphous polymer behavior.

Original languageEnglish (US)
Title of host publication2006 IEEE International Ultrasonics Symposium, IUS
Pages1025-1028
Number of pages4
DOIs
StatePublished - 2006

Publication series

NameProceedings - IEEE Ultrasonics Symposium
Volume1
ISSN (Print)1051-0117

ASJC Scopus subject areas

  • Acoustics and Ultrasonics

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