"The fellow has designed, built and optimized an experimental setup that is capable of imaging through capillary waveguides and multimode fibers using two different imaging modalities: fluorescence and photoacoustic imaging. Besides developing the experimental setup, the fellow had perform simulations for new imaging techniques using the granular speckle patterns produced at the output of the capilllary and the mulitmode fiber. After the simulations showed promising results, their experimental implementation with the setup matched the predicted viability of the proposed method. This novel imaging approach reduce the complexity of the experimental setup and reduce the number of measurements required to form an image at expenses of increasing the computational complexity in the image reconstruction.
Three types of proof-of-principle experiments were performed in this work, namely photoacoustic microscopy alone, fluorescence microscopy alone, and hybrid photoacoustic/fluorescence microscopy. Two types of samples were used to illustrate the photoacoustic imaging capability of the setup. As a well-controlled test sample, we used an absorbing micro-structure photoplotted on a polymer film shown on Fig. 1 a (""power-on"" logo). To further demonstrate the performance of the system on a more relevant biological sample, we used the same system to obtain photoacoustic images of red blood cell shown in Fig. 1c. Fig. 1b and Fig. 1d shown the reconstructed objects using the photoacoustic signals of each speckle pattern projected.
Two types of fluorescent samples were imaged with a similar experimental setup. Fig. 2 a shows a reference widefield fluorescent image of 4 µm orange beads. The image from fluorescence collected at the input/proximal side of fiber is shown in Fig. 2 b, where the complex distribution of beads is well-recovered while preserving the boundaries of both individual and clustered beads. We also performed imaging of red fluorescent retrobeads (0.05 - 0.2µm) from Lumafluor, microinjected into the dorsomedial striatum (DMS) of a mouse brain, which was then sliced and mounted on a microscope slide. As for the first sample, Fig. 2 c shows a reference widefield fluorescent image of the sample. Fig. 2 d shows the corresponding image reconstructed with our approach, and also clearly demonstrates the recovery of individual clusters of retrobeads in neurons.
Finally, we performed an experiment where we obtain both the photoacoustic and fluorescence images of the same sample. The same set of speckle patterns from a unique calibration procedure was used for both photoacoustic and fluorescent imaging. We used a diluted solution composed of red blood cells and 11μm diameter fluorescent particles (Nile red) in PBS. Figure 3a shows the widefield microscope image of the sample using incoherent illumination through the MMF where two fluorescence particles and one red blood cell can be identified. Figure 3b shows the false-color reconstructed photoacoustic image (red) and fluorescence image (green) from the set of signals corresponding to 2048 speckle patterns. The photoacoustic image clearly shows the ability to resolve single red blood cells and it does not have any spurious signal coming from the fluorescence particles as expected. In the fluorescence case, the signal recorded by the PMT only has contributions from the fluorescence particles.
The fellow has attended and presented the work in more than 10 international conferences, has given several invited seminars in 3 different universities and has participate in an outreach activity in a pub in Grenoble."
