Spectral optoacoustic imaging using a scanning transducer

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.