Abstract

A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200  nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry–Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50  mm diameter aperture in steps of 10  μm with an optically defined element size of 64  μm. Two sensors were used, one with a 22  μm thick polymer film spacer and the other with a 38  μm thick spacer providing 3  dB acoustic bandwidths of 39 and 22  MHz, respectively. The measured noise equivalent pressure of the 38  μm sensor was 0.21  kPa over a 20  MHz measurement bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15  μm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300  μm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.

© 2008 Optical Society of America

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Supplementary Material (6)

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