A scanning optoacoustic transducer was used to generate images of biological tissue in vivo. The transducer consisted of an optical fiber for delivery of laser pulses and an annular piezoelectric film. Optoacoustic waves were generated by irradiating the tissue with 5 ns long pulses from an optical parametric oscillator (OPO) which was tuned between 500 and 600 nm. The motorized scanner allowed to generate a 200x200 pixel image within 20 seconds. In images of human skin in vivo, certain structures such as the epidermis, blood capillaries and deeper blood vessels could be localized and identified by their spectral characteristics. From the spectral dependence of blood containing structures the oxygenation level of hemoglobin could be estimated.
Optoacoustic pressure waves were generated by irradiating blood vessels embedded into calf cartilage with 5 ns long pulses from an optical parametric oscillator (OPO). A two dimensional pressure transducer consisting of a glass prism and a liquid layer was used to measure the laser-induced pressure waves. The pressure dependent changes of reflection at the prism-liquid interface were recorded with a time-gated CCD-camera. On the basis of the 2D pressure measurements the spatial distribution of the blood vessels was reconstructed using two different algorithms, one based on radial back projection and one using Fourier transformation. High lateral (100 micrometers ) and depth resolution (20 micrometers ) was achieved.
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