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Photoacoustic (PA) signals were used to detect and image optically absorbing structures in highly scattering media. Tissue phantoms were constructed from 10 μm diameter carbon fibres and nylon vessels containing blood or a variable dilution of Evens blue that were situated within a I% dilution oflntralipid A PVdF piezoelectric hydrophone with a bandwidth of 70 MHZ was used to detect the PA signals. A Q-switched frequency doubled Nd: Y AG laser provided 1 O ns pulses at 1 O Hz repetition rate and 532 nm wavelength. The sensitivity of the PA technique was demonstrated by the photoacoustic detection of single red blood cells that were situated on a glass plate in a PBS buffer. PA images of the samples were constructed from scanned array detection of the acoustic signals. The imaging algorithm is based on scanning synthetic delay-and-sum focus forming. The transducer directivity was simulated, verified and used to determine the weight factors of the algorithm. Threads and capillaries with various diameters situated at various depths have been imaged. The lateral resolution is limited by the diameter (200 μm) of the transducer. In the experimental images is shown that the depth resolution can be less than 10 μm. The accuracy of the source location reconstruction depends both on the method of signal processing and the PA signal duration. The PA images of larger blood vessels in phantom tissue show only the front and back side of these vessels due to the relatively low optical penetration depth in whole blood, acoustic interference and acoustic reflection at the walls of the vessels. The photoacoustic image of optically absorbing characters located at a depth of 1.8 mm and illuminated through 2 mm Intralipid dilution is presented. The results of this study are promising for the development ofphotoacoustic tomography. Keywords: Photoacoustics, imaging, phantom tissue, tomography, blood, piezoelectric detection.
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