Lensless polarimetric coded ptychography for high-resolution,high-throughput gigapixel birefringence imaging on a chip

Polarimetric imaging provides valuable insights into the polarization state of light interacting with a sample.It can infer crucial birefringence properties of specimens without using labels,thereby facilitating the diagnosis of diseases such as cancer and osteoarthritis.In this study,we present a novel polarimetric coded ptychography(pol-CP)approach that enables high-resolution,high-throughput gigapixel birefringence imaging on a chip.Our platform deviates from traditional lens-based systems by employing an integrated polarimetric coded sensor for lensless coherent diffraction imaging.Utilizing Jones calculus,we quantitatively determine the birefringence retardance and orientation information of biospecimens from the recovered images.Our portable pol-CP prototype can resolve the 435 nm linewidth on the resolution target,and the imaging field of view for a single acquisition is limited only by the detector size of 41 mm2.The prototype allows for the acquisition of gigapixel birefringence images with a 180 mm^(2) field of view in~3.5 min,a performance that rivals high-end whole slide scanner but at a small fraction of the cost.To demonstrate its biomedical applications,we perform high-throughput imaging of malaria-infected blood smears,locating parasites using birefringence contrast.We also generate birefringence maps of label-free thyroid smears to identify thyroid follicles.Notably,the recovered birefringence maps emphasize the same regions as autofluorescence images,underscoring the potential for rapid on-site evaluation of label-free biopsies.Our approach provides a turnkey and portable solution for lensless polarimetric analysis on a chip,with promising applications in disease diagnosis,crystal screening,and label-free chemical imaging,particularly in resource-constrained environments.

Complex-domain-enhancing neural network for large-scale coherent imaging

Large-scale computational imaging can provide remarkable space-bandwidth product that is beyond the limit of optical systems.In coherent imaging(CI),the joint reconstruction of amplitude and phase further expands the information throughput and sheds light on label-free observation of biological samples at micro-or even nano-levels.The existing large-scale CI techniques usually require scanning/modulation multiple times to guarantee measurement diversity and long exposure time to achieve a high signal-to-noise ratio.Such cumbersome procedures restrict clinical applications for rapid and lowphototoxicity cell imaging.In this work,a complex-domain-enhancing neural network for large-scale CI termed CI-CDNet is proposed for various large-scale CI modalities with satisfactory reconstruction quality and efficiency.CI-CDNet is able to exploit the latent coupling information between amplitude and phase(such as their same features),realizing multidimensional representations of the complex wavefront.The cross-field characterization framework empowers strong generalization and robustness for various coherent modalities,allowing high-quality and efficient imaging under extremely low exposure time and few data volume.We apply CI-CDNet in various large-scale CI modalities including Kramers–Kronigrelations holography,Fourier ptychographic microscopy,and lensless coded ptychography.A series of simulations and experiments validate that CI-CDNet can reduce exposure time and data volume by more than 1 order of magnitude.We further demonstrate that the high-quality reconstruction of CI-CDNet benefits the subsequent high-level semantic analysis.

Review of bio-optical imaging systems with a high space-bandwidth product

Optical imaging has served as a primary method to collect information about biosystems across scales—from functionalities of tissues to morphological structures of cells and even at biomolecular levels.However,to adequately characterize a complex biosystem,an imaging system with a number of resolvable points,referred to as a space-bandwidth product(SBP),in excess of one billion is typically needed.Since a gigapixel-scale far exceeds the capacity of current optical imagers,compromises must be made to obtain either a low spatial resolution or a narrow field-of-view(FOV).The problem originates from constituent refractive optics—the larger the aperture,the more challenging the correction of lens aberrations.Therefore,it is impractical for a conventional optical imaging system to achieve an SBP over hundreds of millions.To address this unmet need,a variety of high-SBP imagers have emerged over the past decade,enabling an unprecedented resolution and FOV beyond the limit of conventional optics.We provide a comprehensive survey of high-SBP imaging techniques,exploring their underlying principles and applications in bioimaging.

Synthetic aperture ptychography:coded sensor translation for joint spatial-Fourier bandwidth expansion

Conventional ptychography translates an object through a localized probe beam to widen the field of view in real space.Fourier ptychography translates the object spectrum through a pupil aperture to expand the Fourier bandwidth in reciprocal space.Here we report an imaging modality,termed synthetic aperture ptychography(SAP),to get the best of both techniques.In SAP,we illuminate a stationary object using an extended plane wave and translate a coded image sensor at the far field for data acquisition.The coded layer attached on the sensor modulates the object exit waves and serves as an effective ptychographic probe for phase retrieval.The sensor translation process in SAP synthesizes a large complex-valued wavefront at the intermediate aperture plane.By propagating this wavefront back to the object plane,we can widen the field of view in real space and expand the Fourier bandwidth in reciprocal space simultaneously.We validate the SAP approach with transmission targets and reflection silicon microchips.A 20-mm aperture was synthesized using a 5-mm sensor,achieving a fourfold gain in resolution and 16-fold gain in field of view for object recovery.In addition,the thin sample requirement in ptychography is no longer required in SAP.One can digitally propagate the recovered exit wave to any axial position for post-acquisition refocusing.The SAP scheme offers a solution for far-field sub-diffraction imaging without using lenses.It can be adopted in coherent diffraction imaging setups with radiation sources from visible light,extreme ultraviolet,and X-ray,to electron.

Rapid full-color Fourier ptychographic microscopy via spatially filtered color transfer

Full-color imaging is of critical importance in digital pathology for analyzing labeled tissue sections.In our previous cover story[Sci.China:Phys.,Mech.Astron.64,114211(2021)],a color transfer approach was implemented on Fourier ptychographic microscopy(FPM)for achieving high-throughput full-color whole slide imaging without mechanical scanning.The approach was able to reduce both acquisition and reconstruction time of FPM by three-fold with negligible trade-off on color accuracy.However,the method cannot properly stain samples with two or more dyes due to the lack of spatial constraints in the color transfer process.It also requires a high computation cost in histogram matching of individual patches.Here we report a modified full-color imaging algorithm for FPM,termed color-transfer filtering FPM(CFFPM).In CFFPM,we replace the original histogram matching process with a combination of block processing and trilateral spatial filtering.The former step reduces the search of the solution space for colorization,and the latter introduces spatial constraints that match the low-resolution measurement.We further adopt an iterative process to refine the results.We show that this method can perform accurate and fast color transfer for various specimens,including those with multiple stains.The statistical results of 26 samples show that the average root mean square error is only 1.26%higher than that of the red-green-blue sequential acquisition method.For some cases,CFFPM outperforms the sequential method because of the coherent artifacts introduced by dust particles.The reported CFFPM strategy provides a turnkey solution for digital pathology via computational optical imaging.

Incoherent Fourier ptychographic photography using structured light

Controlling photographic illumination in a structured fashion is a common practice in computational photography and image-based rendering. Here we introduce an incoherent photographic imaging approach, termed Fourier ptychographic photography, that uses nonuniform structured light for super-resolution imaging. In this approach,frequency mixing between the object and the structured light shifts the high-frequency object information to the passband of the photographic lens. Therefore, the recorded intensity images contain object information that is beyond the cutoff frequency of the collection optics. Based on multiple images acquired under different structured light patterns, we used the Fourier ptychographic algorithm to recover the super-resolution object image and the unknown illumination pattern. We demonstrated the reported approach by imaging various objects, including a resolution target, a quick response code, a dollar bill, an insect, and a color leaf. The reported approach may find applications in photographic imaging settings, remote sensing, and imaging radar. It may also provide new insights for high-resolution imaging by shifting the focus from the collection optics to the generation of structured light.

Light-field micro-endoscopy using a fiber bundle:a snapshot 3D epi-fluorescence endoscope

Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for in vivo observation of animals.A micro-endoscope that can realize 3D imaging at the camera framerate could benefit various clinical and biological applications.In this work,we report the development of a compact light-field micro-endoscope(LFME)that can obtain snapshot 3D fluorescence imaging,by jointly using a single-mode fiber bundle and a small-size light-field configuration.To demonstrate the real imaging performance of our method,we put a resolution chart in different z positions and capture the z-stack images successively for reconstruction,achieving 333-μm-diameter field of view,24μm optimal depth of field,and up to 3.91μm spatial resolution near the focal plane.We also test our method on a human skin tissue section and He La cells.Our LFME prototype provides epi-fluorescence imaging ability with a relatively small(2-mm-diameter)imaging probe,making it suitable for in vivo detection of brain activity and gastrointestinal diseases of animals.

Effective color transfer enables rapid computational microscopy for digital pathology

In most pathology labs,clinicians diagnose diseases by examining tissue slices using a light microscope.This process typically requires clinicians to move the microscope stage to different positions and identify areas of interest that can be further analyzed using a higher magnification objective lens.For proper focusing of the slide,the axial position needs to be constantly adjusted by manually rotating the focus knob.As a result,the reviewing process can be easily disrupted when the clinician bumps the slide to the objective lens or switches to a different objective lens for focusing again.Although it remains the gold standard in diagnosing almost all types of cancers,manual microscopic inspection is,in general,labor-intensive and does not form a streamlined workflow in clinical practice.Furthermore,it is largely based on subjective opinions of clinicians:different clinicians may arrive at different conclusions for the same slide and the same person may give different conclusions at different time points[1].

Ptycho-endoscopy on a lensless ultrathin fiber bundle tip

Synthetic aperture radar(SAR)utilizes an aircraft-carried antenna to emit electromagnetic pulses and detect the returning echoes.As the aircraft travels across a designated area,it synthesizes a large virtual aperture to improve image resolution.Inspired by SAR,we introduce synthetic aperture ptycho-endoscopy(SAPE)for micro-endoscopic imaging beyond the diffraction limit.SAPE operates by hand-holding a lensless fiber bundle tip to record coherent diffraction patterns from specimens.The fiber cores at the distal tip modulate the diffracted wavefield within a confined area,emulating the role of the‘airborne antenna’in SAR.The handheld operation introduces positional shifts to the tip,analogous to the aircraft’s movement.These shifts facilitate the acquisition of a ptychogram and synthesize a large virtual aperture extending beyond the bundle’s physical limit.We mitigate the influences of hand motion and fiber bending through a low-rank spatiotemporal decomposition of the bundle’s modulation profile.Our tests demonstrate the ability to resolve a 548-nm linewidth on a resolution target.The achieved space-bandwidth product is~1.1 million effective pixels,representing a 36-fold increase compared to that of the original fiber bundle.Furthermore,SAPE’s refocusing capability enables imaging over an extended depth of field exceeding 2 cm.The aperture synthesizing process in SAPE surpasses the diffraction limit set by the probe’s maximum collection angle,opening new opportunities for both fiber-based and distal-chip endoscopy in applications such as medical diagnostics and industrial inspection.