Deep learning assisted variational Hilbert quantitative phase imaging

We propose a high-accuracy artifacts-free single-frame digital holographic phase demodulation scheme for relatively lowcarrier frequency holograms-deep learning assisted variational Hilbert quantitative phase imaging(DL-VHQPI).The method,incorporating a conventional deep neural network into a complete physical model utilizing the idea of residual compensation,reliably and robustly recovers the quantitative phase information of the test objects.It can significantly alleviate spectrum-overlapping-caused phase artifacts under the slightly off-axis digital holographic system.Compared to the conventional end-to-end networks(without a physical model),the proposed method can reduce the dataset size dramatically while maintaining the imaging quality and model generalization.The DL-VHQPI is quantitatively studied by numerical simulation.The live-cell experiment is designed to demonstrate the method's practicality in biological research.The proposed idea of the deep learning-assisted physical model might be extended to diverse computational imaging techniques.

Lens-free on-chip 3D microscopy based on wavelength-scanning Fourier ptychographic diffraction tomography

Lens-free on-chip microscopy is a powerful and promising high-throughput computational microscopy technique due to its unique advantage of creating high-resolution images across the full field-of-view(FOV)of the imaging sensor.Nevertheless,most current lens-free microscopy methods have been designed for imaging only two-dimensional thin samples.Lens-free on-chip tomography(LFOCT)with a uniform resolution across the entire FOV and at a subpixel level remains a critical challenge.In this paper,we demonstrated a new LFOCT technique and associated imaging platform based on wavelength scanning Fourier ptychographic diffraction tomography(wsFPDT).Instead of using angularlyvariable illuminations,in wsFPDT,the sample is illuminated by on-axis wavelength-variable illuminations,ranging from 430 to 1200 nm.The corresponding under-sampled diffraction patterns are recorded,and then an iterative ptychographic reconstruction procedure is applied to fill the spectrum of the three-dimensional(3D)scattering potential to recover the sample’s 3D refractive index(RI)distribution.The wavelength-scanning scheme not only eliminates the need for mechanical motion during image acquisition and precise registration of the raw images but secures a quasi-uniform,pixel-super-resolved imaging resolution across the entire imaging FOV.With wsFPDT,we demonstrate the high-throughput,billion-voxel 3D tomographic imaging results with a half-pitch lateral resolution of 775 nm and an axial resolution of 5.43μm across a large FOV of 29.85mm2 and an imaging depth of>200μm.The effectiveness of the proposed method was demonstrated by imaging various types of samples,including micropolystyrene beads,diatoms,and mouse mononuclear macrophage cells.The unique capability to reveal quantitative morphological properties,such as area,volume,and sphericity index of single cell over large cell populations makes wsFPDT a powerful quantitative and label-free tool for high-throughput biological applications.

Optimal illumination scheme for isotropic quantitative differential phase contrast microscopy

Differential phase contrast microscopy(DPC) provides high-resolution quantitative phase distribution of thin transparent samples under multi-axis asymmetric illuminations. Typically, illumination in DPC microscopic systems is designed with two-axis half-circle amplitude patterns, which, however, result in a non-isotropic phase contrast transfer function(PTF). Efforts have been made to achieve isotropic DPC by replacing the conventional half-circle illumination aperture with radially asymmetric patterns with three-axis illumination or gradient amplitude patterns with two-axis illumination. Nevertheless, the underlying theoretical mechanism of isotropic PTF has not been explored, and thus, the optimal illumination scheme cannot be determined. Furthermore, the frequency responses of the PTFs under these engineered illuminations have not been fully optimized, leading to suboptimal phase contrast and signal-to-noise ratio for phase reconstruction. In this paper, we provide a rigorous theoretical analysis about the necessary and sufficient conditions for DPC to achieve isotropic PTF. In addition,we derive the optimal illumination scheme to maximize the frequency response for both low and high frequencies(from 0 to 2 NAobj) and meanwhile achieve perfectly isotropic PTF with only two-axis intensity measurements.We present the derivation, implementation, simulation, and experimental results demonstrating the superiority of our method over existing illumination schemes in both the phase reconstruction accuracy and noise-robustness.

Transport of intensity diffraction tomography with non-interferometric synthetic aperture for three-dimensional label-free microscopy

We present a new label-free three-dimensional(3D)microscopy technique,termed transport of intensity diffraction tomography with non-interferometric synthetic aperture(TIDT-NSA).Without resorting to interferometric detection,TIDT-NSA retrieves the 3D refractive index(RI)distribution of biological specimens from 3D intensity-only measurements at various illumination angles,allowing incoherent-diffraction-limited quantitative 3D phase-contrast imaging.The unique combination of z-scanning the sample with illumination angle diversity in TIDT-NSA provides strong defocus phase contrast and better optical sectioning capabilities suitable for high-resolution tomography of thick biological samples.Based on an off-the-shelf bright-field microscope with a programmable light-emitting-diode(LED)illumination source,TIDT-NSA achieves an imaging resolution of 206 nm laterally and 520 nm axially with a high-NA oil immersion objective.We validate the 3D RI tomographic imaging performance on various unlabeled fixed and live samples,including human breast cancer cell lines MCF-7,human hepatocyte carcinoma cell lines HepG2,mouse macrophage cell lines RAW 264.7,Caenorhabditis elegans(C.elegans),and live Henrietta Lacks(HeLa)cells.These results establish TIDT-NSA as a new non-interferometric approach to optical diffraction tomography and 3D label-free microscopy,permitting quantitative characterization of cell morphology and time-dependent subcellular changes for widespread biological and medical applications.

Hybrid brightfield and darkfield transport of intensity approach for high-throughput quantitative phase microscopy

Transport of intensity equation(TIE)is a well-established non-interferometric phase retrieval approach that enables quantitative phase imaging(QPI)by simply measuring intensity images at multiple axially displaced planes.The advantage of a TIE-based QPI system is its compatibility with partially coherent illumination,which provides speckle-free imaging with resolution beyond the coherent diffraction limit.However,TIE is generally implemented with a brightfield(BF)configuration,and the maximum achievable imaging resolution is still limited to the incoherent diffraction limit(twice the coherent diffraction limit).It is desirable that TIE-related approaches can surpass this limit and achieve high-throughput[high-resolution and wide field of view(FOV)]QPI.We propose a hybrid BF and darkfield transport of intensity(HBDTI)approach for highthroughput quantitative phase microscopy.Two through-focus intensity stacks corresponding to BF and darkfield illuminations are acquired through a low-numerical-aperture(NA)objective lens.The high-resolution and large-FOV complex amplitude(both quantitative absorption and phase distributions)can then be synthesized based on an iterative phase retrieval algorithm taking the coherence model decomposition into account.The effectiveness of the proposed method is experimentally verified by the retrieval of the USAF resolution target and different types of biological cells.The experimental results demonstrate that the half-width imaging resolution can be improved from 1230 nm to 488 nm with 2.5×expansion across a 4×FOV of 7.19 mm2,corresponding to a 6.25×increase in space-bandwidth product from∼5 to∼30.2 megapixels.In contrast to conventional TIE-based QPI methods where only BF illumination is used,the synthetic aperture process of HBDTI further incorporates darkfield illuminations to expand the accessible object frequency,thereby significantly extending the maximum available resolution from 2NA to∼5NA with a∼5×promotion of the coherent diffraction limit.Given its capability for high-throughput QPI,the proposed HBDTI approach is expected to be adopted in biomedical fields,such as personalized genomics and cancer diagnostics.

Accurate quantitative phase imaging by differential phase contrast with partially coherent illumination:beyond weak object approximation

Quantitative phase imaging(QPI)by differential phase contrast(DPC)with partially coherent illumination provides speckle-free imaging and lateral resolution beyond the coherent diffraction limit,demonstrating great potential in biomedical imaging applications.Generally,DPC employs weak object approximation to linearize the phase-to-intensity image formation,simplifying the solution to the phase retrieval as a two-dimensional deconvolution with the corresponding phase transfer function.Despite its widespread adoption,weak object approximation still lacks a precise and clear definition,suggesting that the accuracy of the QPI results,especially for samples with large phase values,is yet to be verified.In this paper,we analyze the weak object approximation condition quantitatively and explicitly give its strict definition that is applicable to arbitrary samples and illumination apertures.Furthermore,an iterative deconvolution QPI technique based on pseudo-weak object approximation is proposed to overcome the difficulty of applying DPC to large-phase samples without additional data acquisition.Experiments with standard microlens arrays and MCF-7 cells demonstrated that the proposed method can effectively extend DPC beyond weak object approximation to high-precision three-dimensional morphological characterization of large-phase technical and biological samples.