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Viscoelastic properties of normal rat liver measured by ultrasound elastography: Comparison with oscillatory rheometry.

BACKGROUND
Ultrasound elastography has been widely used to measure liver stiffness. However, the accuracy of liver viscoelasticity obtained by ultrasound elastography has not been well established.


OBJECTIVE
To assess the accuracy of ultrasound elastography for measuring liver viscoelasticity and compare to conventional rheometry methods. In addition, to determine if combining these two methods could delineate the rheological behavior of liver over a wide range of frequencies.


METHODS
The phase velocities of shear waves were measured in livers over a frequency range from 100 to 400 Hz using the ultrasound elastography method of shearwave dispersion ultrasound vibrometry (SDUV), while the complex shear moduli were obtained by rheometry over a frequency range of 1 to 30 Hz. Three rheological models, Maxwell, Voigt, and Zener, were fit to the measured data obtained from the two separate methods and from the combination of the two methods.


RESULTS
The elasticity measured by SDUV was in good agreement with that of rheometry. However, the viscosity measured by SDUV was significantly different from that of rheometry.


CONCLUSIONS
The results indicate that the high frequency components of the dispersive data play a much more important role in determining the dispersive pattern or the viscous value than the low frequency components. It was found that the Maxwell model is not as appropriate as the Voigt and Zener models for describing the rheological behavior of liver.