Optical-resolution photoacoustic endomicroscopy (OR-PAE) allows going beyond the limited penetration depth of conventional optical-resolution photoacoustic systems. Recently, it has been shown that OR-PAE may be performed through minimally invasive multimode fibers, by raster scanning a focus spot with optical wavefront shaping . Here we introduce for the first time an approach to perform OR-PAE through a multimode fiber with a full-field illumination approach. By using multiple known speckle patterns, we show that it is possible to obtain optical-diffraction limited photoacoustic images, with the same resolution as that obtained by raster scanning a focus spot, i.e that of the speckle grain size. The fluctuations patterns of the photoacoustic amplitude at each pixel in the sample plane with the series of multiple speckle illumination were used to encode each pixel.
This approach with known speckle illumination requires an initial calibration stage, that consists in learn a set of fluctuation patterns pixel per pixel, which will encode patterns each pixel of the scanned area. A point-like absorber was scanned across the filed-of-view during the calibration stage to acquire the reference patterns. Image reconstruction may be carried out by cross-correlating the series of photoacoustic amplitude measured with the sample to the reference patterns obtained during the calibration stage.
In this work, the approach above was carried out both theoretically with Monte-carlo simulations and experimentally through a multi-mode fiber with samples made of absorbing spheres.
 Papadopoulos et al., " Optical-resolution photoacoustic microscopy by use of a multimode fiber", Appl. Phys. Lett., 102(21), 2013
Florian Poisson and Emmanuel Bossy, "Full-field illumination approach with multiple speckle for optical-resolution photoacoustic microscopy
(Conference Presentation)," Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97080H (Presented at SPIE BiOS: February 14, 2016; Published: 27 April 2016); https://doi.org/10.1117/12.2212561.4828179426001.
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