2B-4 Square-Wave Aperture Weightings for Reception Beam Forming in High Frame Rate Imaging

Abstract

Recently, the high frame rate (HFR) imaging method was extended to include multiple transmission beams such as steered plane waves and limited-diffraction array beams to improve image quality. In addition, limited-diffraction array beam transmissions have been approximated with square-wave aperture weightings so that only one or two transmitters are needed for three-dimensional imaging with a fully populated two-dimensional array transducer, simplifying the transmission subsystem of an imager. In this paper, the square-wave aperture weightings are applied to reception beamforming to simplify the limited-diffraction array beam aperture weightings proposed previously, which allows the production of all spatial frequency components of analog echo signals in realtime over a transducer aperture by direct summation and subtraction of these signals for image reconstructions. This approach reduces the need of some high-speed digital circuits and can also be used as a realtime spatial spectrum analyzer to produce both amplitude and phase of the waves impinging on the surface of a receiver with simple electronics as long as the spatial Nyquist sampling criterion is satisfied. Both in vitro (on an ATS539 phantom) and in vivo (on the hearts and a kidney of volunteers) experiments were performed with a broadband phased array transducer of 2.5 MHz center frequency, 128 elements, and 0.15 mm pitch using a home-made general-purpose HFR imaging system. A one-cycle, 2.5 MHz sine wave pulse was used to excite the transducer with a pulse repetition period of about 187 microseconds. Results show that the quality of images reconstructed with the reception square-wave aperture weightings is very close to that of images reconstructed with the exact limited-diffraction array beam weightings or spatial Fourier transform on echo signals. The images reconstructed have over plusmn45 degree field of view and an image frame rate of about 486/s is achieved for a depth of 120 mm