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27 February 2019 Combination of an annular array with a conical acoustic lens for large depth of field photoacoustic macroscopy
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Photoacoustic macroscopy uses a focused detector scanned across the tissue surface to obtain two- or three-dimensional images. Single element transducers equipped with a spherical acoustic lens suffer from the trade-off between lateral resolution and depth of field (DOF). In order to achieve a large imaging depth with constant lateral resolution over a large depth range, we investigate combinations of concentric ring arrays and acoustic lenses. The ring arrays allow dynamic focusing to a large depth range along the ring axis, and the lenses increase the transducer sensitivity. A photoacoustic sensor array is demonstrated, which consists of piezoelectric ring elements, concentrically arranged relative to a conical acoustic lens. Polymethyl-methacrylate (PMMA) is used as the lens material. A planar polyvinylidene fluoride (PVDF) film with conducting layers on both sides and 110 μm thickness was attached to the PMMA lens. The conducting layer was electrically etched to create several ring electrodes with equal detection area. Laser pulses from a near infrared optical parametric oscillator illuminated the object through the center of the ring array. The properties of the sensor array and the image formation by dynamic focusing are simulated and compared to experimental results. As demonstrated in B-scans of several phantoms, it is possible to achieve a lateral resolution in the range of 300 μm over a depth range of about two centimeter.
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P. R. Torke, R. Nuster, and G. Paltauf "Combination of an annular array with a conical acoustic lens for large depth of field photoacoustic macroscopy", Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 1087853 (27 February 2019);

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