23 February 2012 Signal-to-noise ratio scaled coherence weighting for photoacoustic array imaging
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Ultrasound array systems with conventional delay-and-sum beamformers are often adopted for high frame rate photoacoustic imaging. In this report, we propose a coherence factor (CF) based imaging approach to further improve the image contrast of such array systems by suppressing sidelobes of the acoustic diffraction pattern. Specifically, minimum variance based coherence factor (CFMVDR) is used. Furthermore, because CF-based weighting is susceptible to variations in signal-to-noise-ratio (SNR), we also adopt a Wiener filter approach to alleviate this problem so that the method can perform well under all SNR conditions. This is of particular interest as the SNR in photoacoustic imaging is typically low. To test this method, a human hair and a graphite phantom were used as test subjects. The imaging system consisted of a 523nm pulsed laser, and a 128-channel linear array (bandwidth from 5 to 10MHz) for photoacoustic signal detection. It is demonstrated that the beam widths (i.e., lateral resolution) can be effectively improved and the noise background is suppressed by 20 dB. The contrast improvement is also evident.
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Yu-Hsin Wang, Pai-Chi Li, "Signal-to-noise ratio scaled coherence weighting for photoacoustic array imaging", Proc. SPIE 8223, Photons Plus Ultrasound: Imaging and Sensing 2012, 822340 (23 February 2012); doi: 10.1117/12.909854; https://doi.org/10.1117/12.909854

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