We present a ultra-thin endoscopy system for optical resolution photoacoustic microscopy. The system is based on a silica capillary waveguide of two hundred microns of diameter. The silica tube acts as a multi-mode optical waveguide for the illumination, while the hollow core of the capillary carries a fiber-based optical hydrophone to detect the photoacoustic waves. Embedding the ultrasound detection within the device avoids the absorption of high-frequency ultrasound by the tissue and therefore removes any limitation on the insertion depth.
To control the illumination at the distal tip of the capillary, a digital micromirror device modulates the amplitude of the optical wavefront which is coupled into the capillary. The DMD allows for fast calibration approaches to reach calibration and measurement times of a few seconds, as compared with current approaches limited to hours. We obtain optical-diffraction-limited images with full field illumination recording the intensity of a series of various speckle patterns produced by different configurations of the DMD at the input, with no wavefront shaping. The intensity fluctuations from shot to shot codes for the position at which it is measured. Computational methods based on correlation, pseudo-inverse and compressed sensing approaches are investigated and compared with raster-scanning an optimized focus for image reconstruction. To best of our knowledge, our approach provides the thinest endoscope head capable of obtaining optical resolution photoacoustic images.
Antonio M. Caravaca-Aguirre, Florian Poisson, and Emmanuel Bossy, "A capillary waveguide as an ultrathin optical-resolution photoacoustic endoscope (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 1049413 (Presented at SPIE BiOS: January 29, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2287353.5752215454001.
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