Portable lensless wide-field microscopy imaging platform based on digital inline holography and multi-frame pixel super-resolution

In this paper, an irregular displacement-based lensless wide-field microscopy imaging platform is presented by combining digital in-line holography and computational pixel super-resolution using multi-frame processing. The samples are illuminated by a nearly coherent illumination system, where the hologram shadows are projected into a complementary metal-oxide semiconductor-based imaging sensor. To increase the resolution, a multi-frame pixel resolution approach is employed to produce a single holographic image from multiple frame observations of the scene, with small planar displacements. Displacements are resolved by a hybrid approach: (i) alignment of the LR images by a fast feature-based registration method, and (ii) fine adjustment of the sub-pixel information using a continuous optimization approach designed to find the global optimum solution. Numerical method for phase-retrieval is applied to decode the signal and reconstruct the morphological details of the analyzed sample. The presented approach was evaluated with various biological samples including sperm and platelets, whose dimensions are in the order of a few microns. The obtained results demonstrate a spatial resolution of 1.55 μm on a field-of-view of ≈30 mm 2 . Diagnostic imaging: holograms on the go A lensless microscope capable of generating holograms of biotargets with micrometre-scale detail can potentially improve point-of-care medical testing. Digital holography systems that employ ‘shadow imaging’ – projection of 2D spatial signature of a sample onto an electronic detector – instead of lenses are simpler, smaller, and cheaper than conventional holography systems. Dr. Utkan Demirci from Stanford University School of Medicine and colleagues have used this technology to develop a portable bioimaging device through innovations in instrument design, computational image processing and interpretation. The team built a compact setup that records numerous low-resolution shadow images, and then, applied a feature-based registration method to register data onto the same planar domain. Further adjustment of sub-pixel data with a continuous optimization algorithm yielded ultrasharp images of biological samples, including sperm and platelets, at very wide fields of view.