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Abstract
The simple and compact optics of lensless microscopes and the associated computational algorithms allow for large fields of view and the refocusing of the captured images. However, existing lensless techniques cannot accurately reconstruct the typical low-contrast images of optically dense biological tissue. Here we show that lensless imaging of tissue in vivo can be achieved via an optical phase mask designed to create a point spread function consisting of high-contrast contours with a broad spectrum of spatial frequencies. We built a prototype lensless microscope incorporating the ‘contour’ phase mask and used it to image calcium dynamics in the cortex of live mice (over a field of view of about 16 mm2) and in freely moving Hydra vulgaris, as well as microvasculature in the oral mucosa of volunteers. The low cost, small form factor and computational refocusing capability of in vivo lensless microscopy may open it up to clinical uses, especially for imaging difficult-to-reach areas of the body.
Highlights
IntroductionComputational imaging algorithms, co-designed with optics and sensors, improve the design options for imaging systems[1–3]
The key feature of this phase mask is that it achieves a high-contrast and spatially localized sparse point spread function (PSF) that captures textural frequencies common in natural and biological samples (Fig. 1d)
When we compared the ROIs determined through Robust principal component analysis (RPCA) and K-means from Bio-FlatScope, we found close correspondence to bright individual neurons observed from epifluorescence microscopy (Fig. 4d)
Summary
Computational imaging algorithms, co-designed with optics and sensors, improve the design options for imaging systems[1–3]. Unlike lens-based imaging systems where the goal is to project a reproduction of a (potentially magnified) scene onto an image sensor, a lensless imaging system seeks to produce an invertible transfer function between the incident light field and the sensor measurements These measurements often may not resemble a traditional image[12–18], but contain sufficient information for a computational algorithm to reconstruct an image. The phase mask was designed to produce the target contour-based PSF using a near-field phase retrieval algorithm[3,27] We refer to this prototype device (Fig. 1a) as ‘Bio-FlatScope’ because it achieves a similar flat form factor as the previously reported ‘FlatScope’[10], yet the contour phase mask allows us to perform accurate lensless imaging of biological tissue in vivo
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