Ultrasonic measurements of breast viscoelasticity.
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.
Sridhar
Mallika
M
Department of Biomedical Engineering, University of California, One Shields Avenue, Davis, California 95616, USA.
Insana
Michael F
MF
D000273:Adipose Tissue / Q000000981:diagnostic imaging; D001940:Breast / Q000166:cytology* / Q000502:physiology; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D016014:Linear Models; D017154:Stromal Cells / Q000000981:diagnostic imaging; D013997:Time Factors; D016217:Ultrasonography, Mammary