3 March 2017 Effect of spatial filtering of ultrasound transducers on photoacoustic measurements
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It is intuitively conjectured that the geometrical shape of an ultrasound transducer as well as ultrasound transducer’s transfer function affect the characteristics of measured photoacoustic signals. Previously, we theoretically demonstrated that a photoacoustic spectrum measured by a spherically focused ultrasound transducer exhibits resonance frequency peaks by combining the virtual detector concept with a Green function approach. With experimental demonstrations for photoacoustic resonance peaks, it was discussed that the origin of the photoacoustic resonance is spatial filtering of a limited measurement field of view of a focused ultrasound transducer to generated photoacoustic waves. Also, it was analytically confirmed that a time-domain photoacoustic signal derived from the resonant photoacoustic spectrum shows a temporal bipolar nature. In this Proceeding, we investigate photoacoustic magnitude variation to an absorption coefficient considering photoacoustic resonant spectra and simulated ultrasound transducer transfer functions simultaneously. The results show that a photoacoustic signal magnitude decreases as an absorption coefficient of a photoacoustic object increases after reaching its maximum value. This phenomenon is totally distinct from the commonly accepted sense that a photoacoustic signal magnitude is saturated to an absorption coefficient increase. We analyze the origin of this phenomenon by investigating the relationship between a central frequency of an ultrasound transducer transfer function and photoacoustic resonance frequency.
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DongYel Kang, "Effect of spatial filtering of ultrasound transducers on photoacoustic measurements", Proc. SPIE 10064, Photons Plus Ultrasound: Imaging and Sensing 2017, 100645D (3 March 2017); doi: 10.1117/12.2248767; https://doi.org/10.1117/12.2248767

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