Viscoelastic effects in sonoelastography: impact on tumor detectability

The sonoelastographic theory of tumor detection predicts enhanced image contrast as vibration frequency increases. However, the opposite effect is observed when imaging liver lesions at frequencies (200-400 Hz) where strong viscoelastic effects dominate. Mechanical testing was performed and confirmed the viscoelasticity of liver tissue. The time dependence of the stress relaxation suggests a viscoelastic model with a complex modulus which increases monotonically with frequency. It is shown how this model explains the anomalous frequency effect.