High-frame-rate limited-diffraction beam imaging

Limited-diffraction beams such as Bessel beam, X wave, and array beam are a class of beams that in theory do not spread as they propagate to infinite distance. When realized with a finite aperture, these beams have a large depth of field. In this paper, limited-diffraction beams and their applications to high-frame rate imaging are reviewed and further studied. Using a limited-diffraction beams (in either transmission or reception, or both, or with spatial Fourier transform of received signals), images can be reconstructed in Fourier domain. This significantly reduces the amount of computation in 3D imaging since FFT can be used. As the bandwidth of the transducer is increased, the image reconstructed can cover a larger field of view since a frequency in limited-diffraction beam corresponds to one angular direction of the beam (similar to the “frequency encoding” in the magnetic resonance imaging or MRI). Using the angular dependence with frequency, focused limited-diffraction beams can be used for high-frame-rate and high-resolution tissue property imaging. When limited-diffraction beams are used in transmissions, no time delay (only amplitude weighting) is needed, which simplifies imaging system hardware. Also, flow vector imaging can be obtained with limited-diffraction beams using sine and cosine (quadrature) aperture weighting.