Abstract
Remote generation of shear waves in tissues by radiation force of focused ultrasound is the basis of shear wave elasticity imaging (SWEI), a new acoustic method of medical diagnostics. Feasibility of SWEI was previously demonstrated in the experiments with optical and NMR detection of ultrasonically induced shear waves [Sarvazyan et al., Ultrasound Med. Biol. 24, 1419 (1998)]. In the present study the SWEI system with ultrasonic pulsed Doppler detection of shear waves was designed and tested using a range of gelatin-based phantoms and muscle tissue. Radiation force was generated by a focusing transducer of 8 cm diameter and 7 cm focal length. The carrier frequency was 1 MHz with intensity 1.85 W/cm2 at the surface of the transducer. The Doppler detection transducer operating at 3.5 MHz was installed in the center of the pumping transducer. The developed procedures of tissue motion detection and Doppler signal-processing algorithms based on the autocorrelation method allowed estimation of the velocity with accuracy better than 0.2 mm/s. The waveforms of the shear wave at various distances from the pumping ultrasonic beam axis were measured and the shear wave velocities were evaluated. The oscillation character of relaxation process for some phantoms and muscle tissue was shown experimentally.
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