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Shear wave imaging of in vivo breast tissue by color Doppler shear wave elastography.

ABSTRACT

Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography (color Doppler shear wave imaging: CD SWI) for breast tissue. Continuous shear wave is produced by a small lightweight actuator which is attached to the tissue surface. Shear wave wavefront which propagates in tissue is reconstructed as a binary pattern which consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor high frame rate ultrasound imaging instrument are required to obtain the shear wave wavefront map. Although two conditions, those are shear wave displacement amplitude condition and shear wave frequency condition, are needed in order to obtain map. However, these conditions are not severe restrictions in breast imaging. It is because minimum displacement amplitude is 16 μm for the ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. Directional filter extracts shear wave which propagates in the forward direction. Several maps, such as shear wave phase, velocity and propagation maps, are reconstructed by CD SWI. Accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with ARFI method. Experimental results for breast tissue are shown for shear wave frequency of 296.6 Hz.