Optical-resolution photoacoustic imaging through thick tissue with a thin capillary as a dual optical-in acoustic-out waveguide

We demonstrate the ability to guide high-frequency photoacoustic waves through thick tissue with a water-filled silica-capillary (150 \mu m inner diameter and 30 mm long). An optical-resolution photoacoustic image of a 30 \mu m diameter absorbing nylon thread was obtained by guiding the acoustic waves in the capillary through a 3 cm thick fat layer. The transmission loss through the capillary was about -20 dB, much lower than the -120 dB acoustic attenuation through the fat layer. The overwhelming acoustic attenuation of high-frequency acoustic waves by biological tissue can therefore be avoided by the use of a small footprint capillary acoustic waveguide for remote detection. We finally demonstrate that the capillary can be used as a dual optical-in acoustic-out waveguide, paving the way for the development of minimally invasive optical-resolution photoacoustic endoscopes free of any acoustic or optical elements at their imaging tip.