A pulsed Doppler ultrasonic system design for measuring the viscoelasticity of soft tissue

The viscoelastic properties of biological tissue are critical to functional characteristics of each living organ and fundamental in the analytic modeling of tissue' biomechanical behavior. Recently sonoelasticity, that applies Doppler ultrasound to reflect internal tissue displacements resulting from an externally low-frequency vibration, has being developed to study the elastic modulus and coefficient of viscosity. The purpose of this research was to develop a pulsed Doppler ultrasound system for the quantification of elasticity and viscosity of soft tissue. The design consists of 3.5, 5 and 7.5MHz transducer array, low-frequency vibrator, signal generator, power and instrumentation amplifiers and PC. LabView is implemented to control the system on signal transmitting and receiving and processing data acquisition and analysis. The displacement and phase of vibrated tissues are derived from the spectrum and phase of Doppler signals through phase quadrature demodulation Elastic modulus and coefficient of viscosity are then calculated from these gradients. A feasibility study was conducted on gel phantom and pork experiments. The Doppler signal reflected from vibrated tissues demonstrates significant changes in the phase and displacement Further experiments and signal processing analysis are needed to quantify tissue viscoelasticity from the displacement and phase gradient of Doppler signals.