New Adaptive Beamforming with Spatially-smoothed Coherence Factor: Simulation and Ex vivo Experiment Results

초록

In photoacoustic imaging, an adaptive beamforming method with coherence factor (ABF-CF) was previously introduced for improving spatial resolution and signal-to-noise ratio (SNR) over a conventional delay-and-sum beamforming method (DAS). However, the ABF-CF method is not suitable for being used in practical diagnosis since it is overly-sensitive for off-axis interferences and noises. In this paper, a new adaptive beamforming method with spatially-smoothed coherence factor (ABF-SSCF) is presented for ultrasound and photoacoustic combined imaging to enhance the contrast and spatial resolution while preserving the target information by applying a spatial-smoothing technique into CF coefficients from multiple sub-arrays within an array probe. To evaluate the ABF-SSCF method, computer simulation and ex vivo experiments were conducted. For the computer simulation, 64-channel radio-frequency (RF) data with one channel amplitude-varying off-axis interference was generated. Also, The ex vivo experiments were conducted where 128-channel pre-beamformed RF data were captured from a microcalcification-contained breast core specimen with a commercial ultrasound system equipped with a research package by using a 7-MHz linear array probe (SonixTouch, Ultrasonix Corp., BC, Canada) and an Nd:Yag laser excitation system (Surelite III-10 and Surelite OPO Plus, Continuum Inc., Santa Clara, CA, USA). From the simulation and ex vivo experiments, the proposed ABF-SSCF method provides better contrast and spatial resolutions comparable than the DAS method. Also, compared to the ABF-CF method, image information is clearly presented without being degraded by off-axis interferences. These results indicate that the proposed ABF-SSCF method can simultaneously enhance the image quality and efficacy of the ABF method for ultrasound and photoacoustic combined imaging.

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