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3 March 2014 Combined photoacoustic and speed-of-sound imaging using integrating optical detection
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A setup that allows for the co-registration of photoacoustic (PA) and speed-of-sound (SOS) section images is presented. By means of ultrasound (US) transmission imaging the distribution of the acoustic speed within an object can be obtained. Our method uses the PA effect for the generation of the traversing US waves. Short near-infrared (NIR) laser pulses emitted by a Nd:YAG laser system are used to illuminate external optical absorbing targets at various distances in front of the sample. At the same time the object under investigation is illuminated by a part of the same frequency-doubled laser pulse. A free laser beam, which is part of a Mach-Zehnder interferometer, is used for the detection of the US signals coming from and passing through the sample. Due to a cascaded arrangement of absorbing targets for laser ultrasound (LUS) generation a single laser pulse yields information for a projection of the SOS distribution. The resolution is determined by the number and width of LUS sources. Separation of the signals arriving at the integrating detector is possible because of their different times of flight. After collection of the data reconstruction of a two-dimensional SOS map is accomplished by applying an inverse Radon transform to the projections. For PA section imaging a cylindrical acoustic reflector behind the detector yields an acoustic focus in the observed slice. To the data gathered by detecting the reflected PA signals also the inverse Radon transform is applied to obtain a reconstructed image of the illuminated section. In this paper a detailed description of the setup is given and the results of experiments on two- and three-dimensional phantoms are presented.
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Gerhild Wurzinger, Robert Nuster, Sibylle Gratt, and Günther Paltauf "Combined photoacoustic and speed-of-sound imaging using integrating optical detection", Proc. SPIE 8943, Photons Plus Ultrasound: Imaging and Sensing 2014, 89433L (3 March 2014);

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