Towards kidney histophysiology by using Fourier ptychography

Abstract

Tissue physiology and especially pathology need a cutting-edge microscopic technique capable of imaging tissue morphology and functioning over a wide view with high-resolution details. Fourier Ptychography (FP), a quantitative phase image (QPI) method, overcomes this trade-off relying on the synthetic numerical aperture (NA) principle. FP uses low NA microscope objectives for having huge FoV and multiple illumination angles to synthetize a big NA. Moreover, FP furnishes phase contrast images in a stain-free modality after applying phase retrieval algorithms. The retrieved phase maps allow the possibility of extracting quantitative information about the sample, e.g. refractive index variation, physical thickness and consequently the 3D profile. Here, we apply FP to the analysis of kidney tissues. Both stain-free and stained slides with different dyes and thicknesses are considered. FP phase images are obtained and compared to light-microscopy images of the same slides to discuss the capability of QPI in describing the morphology of kidney samples. Usually, haematoxylin and eosin (H&E) stain is considered a gold standard to make pathological inference on sick tissues because it marks cell nuclei. We propose a new way of observing renal inner structures such as glomeruli and tubules, which are clearly visible without staining. This work could lead physicians to use stainfree phase-contrast images, paving the way to extract FP diagnostic and prognostic biomarkers to enrich pathomic. We reach ~ 0.5 µm of resolution over an area of 3.3 mm2 for each sample up to 10 µm of tissue thickness.