Ultrasonic measurements of breast viscoelasticity

Abstract

In vivo measurements of the viscoelastic properties of breast tissue are described. Ultrasonic echo frames were recorded from volunteers at 5 fps while applying a uniaxial compressive force (1-20 N) within a 1 s ramp time and holding the force constant for up to 200 s. A time series of strain images was formed from the echo data, spatially averaged viscous creep curves were computed, and viscoelastic strain parameters were estimated by fitting creep curves to a second-order Voigt model. The useful strain bandwidth from this quasi-static ramp stimulus was 10(-2) < or = omega < or = 10(0) rad/s (0.0016-0.16 Hz). The stress-strain curves for normal glandular tissues are linear when the surface force applied is between 2 and 5 N. In this range, the creep response was characteristic of biphasic viscoelastic polymers, settling to a constant strain (arrheodictic) after 100 s. The average model-based retardance time constants for the viscoelastic response were 3.2 +/- 0.8 and 42.0 +/- 28 s. Also, the viscoelastic strain amplitude was approximately equal to that of the elastic strain. Above 5 N of applied force, however, the response of glandular tissue became increasingly nonlinear and rheodictic, i.e., tissue creep never reached a plateau. Contrasting in vivo breast measurements with those in gelatin hydrogels, preliminary ideas regarding the mechanisms for viscoelastic contrast are emerging.

Magnetomotive optical coherence elastography for microrheology of biological tissues

“…However, the damping in these tissue specimens is much faster than in tissue phantoms as only one (in the case of lung) or less (in the case of muscle) cycle of oscillation is observed. Moreover, the tissues undergo 33 It is apparent that muscle experiences a steeper creep than lung, while the amplitude of its underdamped oscillation is relatively smaller. Also, when the magnetic field is turned off and the MNPs (and thus the forces on the tissue) are released, the tissue does not revert to its initial position, and some residual strain is present, more so in muscle than in lung.…”

Material properties from acoustic radiation force step response

“…Gelatin hydrogels are structurally simpler, homogeneous, and able to mimic some properties of breast stroma as required for imaging system development. 12 However, hydrogels do not mimic cell-driven dynamic properties normally associated with malignant progression or responses to treatment; many of these features are assumed associated with tumor contrast. Rodent models of mammary cancer can accurately represent genomic, biochemical, metabolic, and some perfusion aspects of tumor physiology, 13 but are less representative of the macrostructures of human breast tumors that strongly influence mechanical behavior.…”

“…Quasi-static methods interrogate tissues at a very low applied-load frequency bandwidth that is bounded from above at approximately 1 Hz and from below at 0.01 Hz depending on the total acquisition time for the strain image recording sequence. 12 At the other load bandwidth extreme are acoustic radiation force imaging methods. 5 A focused push-pulse applies a weak impulse force deep in tissue for about 1 ms after which displacements are imaged in time as the tissue relaxes.…”

Hemodynamic signature of breast cancer under fractional mammographic compression using a dynamic diffuse optical tomography system

“…Such hemodynamic changes are governed by the interplay of biomechanical properties and metabolic activity. Both stiffness as well as oxygen consumption and blood flow [14,15] are known to be elevated in malignant tumors [16,17], motivating the development of a noninvasive imaging technique sensitive to these parameters. In two previous publications, we reported preliminary data in a group of healthy volunteers showing that tissue viscoelastic relaxation during compression modulates both blood volume and hemoglobin oxygen saturation.…”