Transparent ITO coated PVDF transducer for optoacoustic depth profiling

Abstract

In optoacoustic depth profiling, illumination of absorbing biological tissue with short laser pulses generates pressure transients that are recorded with an acoustic transducer. The time profile of these pressure transients mirrors the depth resolved light absorption in the tissue, a relevant parameter, for example for transcutaneous medication penetration or in diagnosis of portwine stain. We propose a novel piezoelectric polyvinylidene fluoride transducer with transparent indium tin oxide (ITO) electrodes. The possibility of laser illumination through the transducer allows backward mode optoacoustic detection, a prerequisite to all parts of the human body not accessible from two sides. The sensitivity of the ITO transducer is comparable to classical metal coated transducers. Its transparency allows direct placement on the skin and combined with homogeneous large area illumination a one-dimensional acoustic propagation model becomes valid. This eliminates the need for computational compensation of diffraction effects. The influence of illumination area was illustrated in a comparison of the two transducers with an absorbing methylene blue sample in forward and backward mode.