Neural-field-assisted transport-of-intensity phase microscopy: partially coherent quantitative phase imaging under unknown defocus distance

The transport-of-intensity equation(TIE) enables quantitative phase imaging(QPI) under partially coherent illumination by measuring the through-focus intensities combined with a linearized inverse reconstruction algorithm. However, overcoming its sensitivity to imaging settings remains a challenging problem because of the difficulty in tuning the optical parameters of the imaging system accurately and because of the instability to long-time measurements. To address these limitations, we propose and experimentally validate a solution called neural-field-assisted transport-of-intensity phase microscopy(NFTPM) by introducing a tunable defocus parameter into neural field. Without weak object approximation, NFTPM incorporates the physical prior of partially coherent image formation to constrain the neural field and learns the continuous representation of phase object without the need for training. Simulation and experimental results of He La cells demonstrate that NFTPM can achieve accurate, partially coherent QPI under unknown defocus distances, providing new possibilities for extending applications in live cell biology.

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.

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.