Changhan Yoon, Yangmo Yoo, Tai-Kyong Song, and Jin Ho Chang
Photoacoustic imaging, sound speed estimation, beamforming, nonlinear anisotropic diffusion, microcalcification
Photoacoustic imaging (PAI) based on an array transducer involves a delay-and-sum beamforming (DAS-BF) method using an assumed fixed sound speed, e.g., 1540 m/s. However, true sound speed in soft tissues varies approximately 1450 m/s to 1600 m/s, leading to degradation of the PAI quality. In this paper, a method for estimating an optimal sound speed is proposed to enhance the quality of cross-sectional PAI. In the method, the modified nonlinear anisotropic diffusion (MNAD) is utilized to reduce the artifacts stemming from the defocusing of ultrasound waves and quality of PAI is quantified using the edge conspicuity (EC). In addition, a standard optimization method (e.g., golden section search) is employed for real-time operation of the proposed method. The performances of the method were evaluated with ex vivo experiments. The results demonstrated that improvement of PA image quality can be achieved when the optimal sound speed estimated by the proposed method is utilized.
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