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Laser line scanning illumination scheme for the enhancement of contrast and resolution for fluorescence reflectance imaging

Intraoperative fluorescence imaging in reflectance geometry is an attractive imaging modality as it allows to noninvasively monitor fluorescence targeted tumors located below the tissue surface. The drawbacks of this technique are the poor resolution in the axial and lateral directions due to multiple light scattering and background fluorescence decreasing the contrast. We propose a novel fluorescence imaging method based on laser line illumination in reflectance geometry. We scan the medium with the laser line and acquire images at each position of the line. We then detect only single stripes of each image located on the excitation line or farther from it. We can also subtract the surrounding signal to the detected stripe, the optimal detection scheme depending on the depth of the object of interest. This allows us to reduce the contribution of parasite signals such as background fluorescence or excitation leaks and also enhances the resolution. These operations on the images can either be digitally done in post-processing or can directly be hardware implemented, allowing our method to be integrated in a handheld device for real-time use. This technique has been validated with tissue-like liquid phantoms with different levels of background fluorescence. Fluorescent inclusions are observed in several configurations at depths ranging from 1 mm to 1 cm. Our results are compared to those obtained with a more classical wide-field detection scheme. Finally, we propose a setup to optically implement the masking detection that will dramatically fasten the detection scheme and optimize the fluorescence light throughput of the system.