Elasticity imaging of polymeric media.

Area of Science:

• Biophysics
• Materials Science
• Biomedical Engineering

Background:

• Viscoelastic properties of soft tissues and hydropolymers are determined by molecular bonding forces.
• Disease processes can alter these molecular bonds, affecting tissue stiffness and viscosity, which is the basis for diagnostic imaging.

Purpose of the Study:

• To review linear viscoelastic theory for interpreting elasticity imaging in soft biological tissues at a molecular scale.
• To investigate the limitations of viscoelastic parameters under various imaging conditions using gelatin hydrogels.

Main Methods:

• Applied quasi-static (step-and-hold, low-frequency harmonic) stimuli to gelatin gels during creep and stress relaxation experiments.
• Conducted experiments in both confined and unconfined geometries.
• Analyzed continuous, bimodal distributions of respondance times.

Main Results:

• Gelatin exhibits solid-like or fluid-like behavior depending on stimulus magnitude within the linear response range.
• Unbiased imaging parameter estimates require creep data acquisition exceeding twice the highest retardance time and elimination of steady-state viscous response.
• Elastic strain and retardance time images offer optimal contrast and signal strength in gelatin.

Conclusions:

• Retardance times reflect fast fluid flow (1-10s) and slow matrix restructuring (50-400s) in response to mechanical stimuli.
• Gelatin's behavior statistically described by low-order rheological models forms the basis for viscoelastic imaging.
• Elasticity imaging provides unique insights into structural and biochemical features of connective tissues affected by disease, using gelatin as a model polymer.