Nyquist-exceeding high voxel rate acquisition in mesoscopic multiphoton microscopy for full-field submicron resolution resolvability

Rapid digital pathology of H&E-stained fresh human brain specimens as an alternative to frozen biopsy

BACKGROUND

Hematoxylin and Eosin (H&E)-based frozen section (FS) pathology is presently the global standard for intraoperative tumor assessment (ITA). Preparation of frozen section is labor intensive, which might consume up-to 30 minutes, and is susceptible to freezing artifacts. An FS-alternative technique is thus necessary, which is sectioning-free, artifact-free, fast, accurate, and reliably deployable without machine learning and/or additional interpretation training.

METHODS

We develop a training-free true-H&E Rapid Fresh digital-Pathology (the-RFP) technique which is 4 times faster than the conventional preparation of frozen sections. The-RFP is assisted by a mesoscale Nonlinear Optical Gigascope (mNLOG) platform with a streamlined rapid artifact-compensated 2D large-field mosaic-stitching (rac2D-LMS) approach. A sub-6-minute True-H&E Rapid whole-mount-Soft-Tissue Staining (the-RSTS) protocol is introduced for soft/frangible fresh brain specimens. The mNLOG platform utilizes third harmonic generation (THG) and two-photon excitation fluorescence (TPEF) signals from H and E dyes, respectively, to yield the-RFP images.

RESULTS

We demonstrate the-RFP technique on fresh excised human brain specimens. The-RFP enables optically-sectioned high-resolution 2D scanning and digital display of a 1 cm² area in <120 seconds with 3.6 Gigapixels at a sustained effective throughput of >700 M bits/sec, with zero post-acquisition data/image processing. Training-free blind tests considering 50 normal and tumor-specific brain specimens obtained from 8 participants reveal 100% match to the respective formalin-fixed paraffin-embedded (FFPE)-biopsy outcomes.

CONCLUSIONS

We provide a digital ITA solution: the-RFP, which is potentially a fast and reliable alternative to FS-pathology. With H&E-compatibility, the-RFP eliminates color- and morphology-specific additional interpretation training for a pathologist, and the-RFP-assessed specimen can reliably undergo FFPE-biopsy confirmation.

Label-free photothermal optical coherence microscopy to locate desired regions of interest in multiphoton imaging of volumetric specimens

Biochip-based research is currently evolving into a three-dimensional and large-scale basis similar to the in vivo microenvironment. For the long-term live and high-resolution imaging in these specimens, nonlinear microscopy capable of label-free and multiscale imaging is becoming increasingly important. Combination with non-destructive contrast imaging will be useful for effectively locating regions of interest (ROI) in large specimens and consequently minimizing photodamage. In this study, a label-free photothermal optical coherence microscopy (OCM) serves as a new approach to locate the desired ROI within biological samples which are under investigation by multiphoton microscopy (MPM). The weak photothermal perturbation in sample by the MPM laser with reduced power was detected at the endogenous photothermal particles within the ROI using the highly sensitive phase-differentiated photothermal (PD-PT) OCM. By monitoring the temporal change of the photothermal response signal of the PD-PT OCM, the hotspot generated within the sample focused by the MPM laser was located on the ROI. Combined with automated sample movement in the x-y axis, the focal plane of MPM could be effectively navigated to the desired portion of a volumetric sample for high-resolution targeted MPM imaging. We demonstrated the feasibility of the proposed method in second harmonic generation microscopy using two phantom samples and a biological sample, a fixed insect on microscope slide, with dimensions of 4 mm wide, 4 mm long, and 1 mm thick.

Construction of a high-NFOM multiphoton microscope with large-angle resonant raster scanning

A resonant-scanning multiphoton optical microscope (MPM) with a millimeter-scale field-of-view (FOV) often encounters a poor Nyquist figure-of-merit (NFOM), leading to an aliasing effect owing to limited effective voxel-sampling rate. In this protocol, we provide a design guideline to enable high-NFOM MPM imaging while simultaneously securing a large FOV/digital-resolution ratio and a fast resonant raster-scanning speed. We further provide a free version of our custom acquisition software to assist with a smooth and easy construction process.

For complete details on the use and execution of this protocol, please refer to Borah et al. (2021).

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Critical guidelines to build a high-NFOM laser-scanning multiphoton optical microscope

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An optimized optical design for large-angle resonant-galvo raster scanning

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A simplified electronic design for high-speed raster scanning

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A free-version of C++ based control and acquisition software (LASERaster⁺)

A rapid denoised contrast enhancement method digitally mimicking an adaptive illumination in submicron-resolution neuronal imaging

Optical neuronal imaging often shows ultrafine structures, such as a nerve fiber, coexisting with ultrabright structures, such as a soma with a substantially higher fluorescence-protein concentration. Owing to experimental and environmental factors, a laser-scanning multiphoton optical microscope (MPM) often encounters a high-frequency background noise that might contaminate such weak-intensity ultrafine neuronal structures. A straightforward contrast enhancement often leads to the saturation of the brighter ones, and might further amplify the high-frequency background noise. We report a digital approach called rapid denoised contrast enhancement (DCE), which digitally mimics a hardware-based adaptive/controlled illumination technique by means of digitally optimizing the signal strengths and hence the visibility of such weak-intensity structures while mostly preventing the saturation of the brightest ones. With large field-of-view (FOV) two-photon excitation fluorescence (TPEF) neuronal imaging, we validate the effectiveness of DCE over state-of-the-art digital image processing algorithms. With compute-unified-device-architecture (CUDA)-acceleration, a real-time DCE is further enabled with a reduced time complexity.

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A real-time applicable CUDA-accelerated Noise-suppressed Contrast Enhancement method

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Digitally mimics a traditional hardware-based adaptive/controlled illumination

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Drastically improves the visibility of noise-contaminated ultrafine neuronal structures

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Applicable in large-field high-NFOM multiphoton optical microscopes