Scattering-Based Light-Sheet Microscopy Imaging of Human Papillomavirus-Associated Squamous Lesions of the Anal Canal: A Proof-of-Principle Study.

Demand for anal cancer screening is expected to rise following the recent publication of the Anal Cancer-HSIL Outcomes Research trial, which showed that treatment of high-grade squamous intraepithelial lesions significantly reduces the rate of progression to anal cancer. While screening for human papillomavirus-associated squamous lesions in the cervix is well established and effective, this is less true for other sites in the lower anogenital tract. Current anal cancer screening and prevention rely on high-resolution anoscopy with biopsies. This procedure has a steep learning curve for providers and may cause patient discomfort. Scattering-based light-sheet microscopy (sLSM) is a novel imaging modality with the potential to mitigate these challenges through real-time, microscopic visualization of disease-susceptible tissue. Here, we report a proof-of-principle study that establishes feasibility of dysplasia detection using an sLSM device. We imaged 110 anal biopsy specimens collected prospectively at our institution's dysplasia clinic (including 30 nondysplastic, 40 low-grade squamous intraepithelial lesion, and 40 high-grade squamous intraepithelial lesion specimens) and found that these optical images are highly interpretable and accurately recapitulate histopathologic features traditionally used for the diagnosis of human papillomavirus-associated squamous dysplasia. A reader study to assess diagnostic accuracy suggests that sLSM images are noninferior to hematoxylin and eosin images for the detection of anal dysplasia (sLSM accuracy = 0.87; hematoxylin and eosin accuracy = 0.80; P = .066). Given these results, we believe that sLSM technology holds great potential to enhance the efficacy of anal cancer screening by allowing accurate sampling of diagnostic tissue at the time of anoscopy. While the current imaging study was performed on ex vivo biopsy specimens, we are currently developing a handheld device for in vivo imaging that will provide immediate microscopic guidance to high-resolution anoscopy providers.

Handheld cross-polarised microscope for imaging individual pigmented cells in human skin in vivo.

We present the development of a simple, handheld cross-polarised microscope (CPM) and demonstration of imaging individual pigmented cells in human skin in vivo. In the CPM device, the cross-polarised detection approach is used to reduce the specular reflection from the skin surface and preferentially detect multiply-scattered light. The multiply-scattered light works as back illumination from within the tissue towards the skin surface, and superficial pigment such as intraepidermal melanin absorbs some spectral bands of the multiply-scattered light and cast coloured shadows. Since the light that interacted with the superficial pigment only needs to travel a short distance before it exits the skin surface, microscopic details of the pigment can be preserved. The CPM device uses a water-immersion objective lens with a high numerical aperture to image the microscopic details with minimal spherical aberrations and a small depth of focus. Preliminary results from a pilot study of imaging skin lesions in vivo showed that the CPM device could reveal three-dimensional distribution of pigmented cells and intracellular distribution of pigment. Co-registered CPM and reflectance confocal microscopy images showed good correspondence between dark, brown cells in CPM images and bright, melanin-containing cells in reflectance confocal microscopy images.

High-speed reflectance confocal microscopy of human skin at 1251-1342 nm.

OBJECTIVES: Reflectance confocal microscopy (RCM) is an imaging method that can noninvasively visualize microscopic features of the human skin. The utility of RCM can be further improved by increasing imaging speed. In this paper, we report high-speed RCM imaging of human skin with a frame rate that is over 10 times faster and an area imaging rate that is 6-9 times faster than those of commercially available RCM devices. METHODS: The higher imaging speed was achieved using a high-speed RCM technique, termed spectrally encoded confocal microscopy (SECM). SECM uses a diffraction grating and a high-speed, wavelength-swept source to conduct confocal imaging at a very high rate. We developed a handheld SECM probe using a scanned-grating approach. The SECM probe was used in conjunction with a wavelength-swept source with a spectral band of 1251-1342 nm. RESULTS: The SECM probe achieved high lateral resolution of 1.3-1.6 µm and an axial resolution of 3.5 µm. SECM images of the human skin (image size = 439 × 439 µm2 ) obtained at 100 frames/s clearly show previously reported RCM features of the human skin in vivo with adequate image quality. The fast imaging speed allowed for the rapid acquisiton of volumetric SECM image data (200 frames covering a depth range of 200 µm) within 2 s. The use of 1251-1342 nm provided sufficient signal level and contrast required to visualize key cellular morphologic features. CONCLUSIONS: These preliminary results demonstrate that high-speed SECM imaging of the human skin at 1251-1342 nm is feasible.

Imaging the dynamics and microstructure of fibrin clot polymerization in cardiac surgical patients using spectrally encoded confocal microscopy.

During cardiac surgery with cardiopulmonary bypass (CPB), altered hemostatic balance may disrupt fibrin assembly, predisposing patients to perioperative hemorrhage. We investigated the utility of a novel device termed spectrally-encoded confocal microscopy (SECM) for assessing fibrin clot polymerization following heparin and protamine administration in CPB patients. SECM is a novel, high-speed optical approach to visualize and quantify fibrin clot formation in three dimensions with high spatial resolution (1.0 µm) over a volumetric field-of-view (165 × 4000 × 36 µm). The measurement sensitivity of SECM was first determined using plasma samples from normal subjects spiked with heparin and protamine. Next, SECM was performed in plasma samples from patients on CPB to quantify the extent to which fibrin clot dynamics and microstructure were altered by CPB exposure. In spiked samples, prolonged fibrin time (4.4 ± 1.8 to 49.3 ± 16.8 min, p < 0.001) and diminished fibrin network density (0.079 ± 0.010 to 0.001 ± 0.002 A.U, p < 0.001) with increasing heparin concentration were reported by SECM. Furthermore, fibrin network density was not restored to baseline levels in protamine-treated samples. In CPB patients, SECM reported lower fibrin network density in protaminized samples (0.055 ± 0.01 A.U. [Arbitrary units]) vs baseline values (0.066 ± 0.009 A.U.) (p = 0.03) despite comparable fibrin time (baseline = 6.0 ± 1.3, protamine = 6.4 ± 1.6 min, p = 0.5). In these patients, additional metrics including fibrin heterogeneity, length and straightness were quantified. Note, SECM revealed that following protamine administration with CPB exposure, fibrin clots were more heterogeneous (baseline = 0.11 ± 0.02 A.U, protamine = 0.08 ± 0.01 A.U, p = 0.008) with straighter fibers (baseline = 0.918 ± 0.003A.U, protamine = 0.928 ± 0.0006A.U. p < 0.001). By providing the capability to rapidly visualize and quantify fibrin clot microstructure, SECM could furnish a new approach for assessing clot stability and hemostasis in cardiac surgical patients.

Deep Learning-Based Denoising in High-Speed Portable Reflectance Confocal Microscopy.

BACKGROUND AND OBJECTIVE: Portable confocal microscopy (PCM) is a low-cost reflectance confocal microscopy technique that can visualize cellular details of human skin in vivo. When PCM images are acquired with a short exposure time to reduce motion blur and enable real-time 3D imaging, the signal-to-noise ratio (SNR) is decreased significantly, which poses challenges in reliably analyzing cellular features. In this paper, we evaluated deep learning (DL)-based approach for reducing noise in PCM images acquired with a short exposure time. STUDY DESIGN/MATERIALS AND METHODS: Content-aware image restoration (CARE) network was trained with pairs of low-SNR input and high-SNR ground truth PCM images obtained from 309 distinctive regions of interest (ROIs). Low-SNR input images were acquired from human skin in vivo at the imaging speed of 180 frames/second. The high-SNR ground truth images were generated by registering 30 low-SNR input images obtained from the same ROI and summing them. The CARE network was trained using the Google Colaboratory Pro platform. The denoising performance of the trained CARE network was quantitatively and qualitatively evaluated by using image pairs from 45 unseen ROIs. RESULTS: CARE denoising improved the image quality significantly, increasing similarity with the ground truth image by 1.9 times, reducing noise by 2.35 times, and increasing SNR by 7.4 dB. Banding noise, prominent in input images, was significantly reduced in CARE denoised images. CARE denoising provided quantitatively and qualitatively better noise reduction than non-DL filtering methods. Qualitative image assessment by three confocal readers showed that CARE denoised images exhibited negligible noise more often than input images and non-DL filtered images. CONCLUSIONS: Results showed the potential of using a DL-based method for denoising PCM images obtained at a high imaging speed. The DL-based denoising method needs to be further trained and tested for PCM images obtained from disease-suspicious skin lesions.

Scattering-Based Light-Sheet Microscopy for Rapid Cellular Imaging of Fresh Tissue.

BACKGROUND AND OBJECTIVES: Light-sheet microscopy (LSM) is a novel imaging technology that has been used for imaging fluorescence contrast in basic life science research. In this paper, we have developed a scattering-based LSM (sLSM) for rapidly imaging the cellular morphology of fresh tissues without any exogenous fluorescent dyes. STUDY DESIGN/MATERIALS AND METHODS: In the sLSM device, a thin light sheet with the central wavelength of 834 nm was incident on the tissue obliquely, 45° relative to the tissue surface. The detection optics was configured to map the light sheet-illuminated area onto a two-dimensional imaging sensor. The illumination numerical aperture (NA) was set as 0.0625, and the detection NA 0.3. RESULTS: The sLSM device achieved a light sheet thickness of less than 6.7 µm over 284 µm along the illumination optical axis. The detection optics of the sLSM device had a resolution of 1.8 µm. The sLSM images of the swine kidney ex vivo visualized tubules with similar sizes and shapes to those observed in histopathologic images. The swine duodenum sLSM images revealed cell nuclei and villi architecture in superficial lesions and glands in deeper regions. CONCLUSIONS: The preliminary results suggest that sLSM may have the potential for rapidly examining the freshly-excised tissue ex vivo or intact tissue in vivo at microscopic resolution. Further optimization and performance evaluation of the sLSM technology will be needed in the future. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Speckle-free, near-infrared portable confocal microscope.

We have developed a portable confocal microscope (PCM) that uses an inexpensive near-infrared LED as the light source. Use of the spatially incoherent light source significantly reduced the speckle contrast. The PCM device was manufactured at the material cost of approximately $5000 and weighed only 1 kg. Lateral and axial resolutions were measured as 1.6 and 6.0 µm, respectively. Preliminary in vivo skin imaging experiment results showed that the PCM device could visualize characteristic cellular features of human skin extending from the stratum corneum to the superficial dermis. Dynamic imaging of blood flow in vivo was also demonstrated. The capability to visualize cellular features up to the superficial dermis is expected to facilitate evaluation and clinical adoption of this low-cost diagnostic imaging tool.

High-Resolution, Wide-Field, Forward-Viewing Spectrally Encoded Endoscope.

BACKGROUND AND OBJECTIVE: Spectrally encoded endoscopy (SEE) is an optical imaging technology that uses spatial wavelength multiplexing to conduct endoscopy in miniature, small diameter probes. Contrary to the previous side-viewing SEE devices, forward-viewing SEE probes are advantageous as they provide a look ahead that facilitates navigation and surveillance. The objective of this work was to develop a miniature forward-viewing SEE probe with a wide field of view and a high spatial resolution. MATERIALS AND METHODS: We designed and developed a forward-viewing SEE device with an overall total diameter of 1.27 mm, which consists of a monolithic illumination probe with a length of 3.87 mm and a diameter of 500 µm, 8 multimode detection fibers that were polished at a 17° angle, a rotational scanning mechanism, and a sheath. The SEE device was evaluated using a USAF resolution target and was used for preclinical imaging of a swine joint ex vivo. RESULTS: This design resulted in a high resolution probe (best spatial resolution of 20.3 µm), a wide total angular field of view of 100°, and an effective number of imaging elements of ~344,000 pixels. The SEE probe performance was compared to a commercial color chip-on-the-tip endoscope; while monochrome, results showed better spatial resolution and a wider field of view for the SEE device. CONCLUSION: These results demonstrate the potential of this forward-viewing SEE probe for visualization and navigation in medical imaging applications. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

A miniaturized, tethered, spectrally-encoded confocal endomicroscopy capsule.

BACKGROUND AND OBJECTIVE: The tethered spectrally-encoded confocal endomicroscopy (SECM) capsule is an imaging device that once swallowed by an unsedated patient can visualize cellular morphologic changes associated with gastrointestinal (GI) tract diseases in vivo. Recently, we demonstrated a tethered SECM capsule for counting esophageal eosinophils in patients with eosinophilic esophagitis (EoE) in vivo. Yet, the current tethered SECM capsule is far too long to be widely utilized for imaging pediatric patients, who constitute a major portion of the EoE patient population. In this paper, we present a new tethered SECM capsule that is 33% shorter, has an easier and repeatable fabrication process, and produces images with reduced speckle noise. MATERIALS AND METHODS: The smaller SECM capsule utilized a miniature condenser to increase the fiber numerical aperture and reduce the capsule length. A custom 3D-printed holder was developed to enable easy and repeatable device fabrication. A dual-clad fiber (DCF) was used to reduce speckle noise. RESULTS: The fabricated SECM capsule (length = 20 mm; diameter = 7 mm) had a similar size and shape to a pediatric dietary supplement pill. The new capsule achieved optical sectioning thickness of 13.2 µm with a small performance variation between devices of 1.7 µm. Confocal images of human esophagus obtained in vivo showed the capability of this new device to clearly resolve microstructural epithelial details with reduced speckle noise. CONCLUSIONS: We expect that the smaller size and better image performance of this new SECM capsule will greatly facilitate the clinical adoption of this technology in pediatric patients and will enable more accurate assessment of EoE-suspected tissues. Lasers Surg. Med. 51:452-458, 2019. © 2019 Wiley Periodicals, Inc.

Single-beam spectrally encoded color imaging.

We have developed, to the best of our knowledge, a new method of conducting spectrally encoded color imaging using a single light beam. In our method, a single broadband light beam was incident on a diffraction grating, where the overlapped third order of the red, fourth order of the green, and fifth order of the blue spectral bands were focused on a line illuminating tissue. This configuration enabled each point on the line to be illuminated by three distinctive wavelengths, corresponding to red, green, and blue. A custom grating was designed and fabricated to achieve high diffraction efficiencies for the wavelengths and diffraction orders used for color spectrally encoded imaging. A bench system was built to test the new spectrally encoded color imaging method. For a beam diameter of 174 µm, the bench system achieved 89,000 effective pixels over a 70° circular field. Spectrally encoded color images of excised swine tissue revealed blood vessels with a similar color appearance to those obtained via a conventional color camera. The results suggest that this single-beam spectrally encoded color method is feasible and can potentially simplify color spectrally encoded endoscopy probe designs.

Large-area spectrally encoded confocal endomicroscopy of the human esophagus in vivo.

BACKGROUND AND OBJECTIVE: Diagnosis of esophageal diseases is often hampered by sampling errors that are inherent in endoscopic biopsy, the standard of care. Spectrally encoded confocal microscopy (SECM) is a high-speed reflectance confocal endomicroscopy technology that has the potential to visualize cellular features from large regions of the esophagus, greatly decreasing the likelihood of sampling error. In this paper, we report results from a pilot clinical study imaging the human esophagus in vivo with a prototype SECM endoscopic probe. MATERIALS AND METHODS: In this pilot clinical study, six patients undergoing esophagogastroduodenoscopy (EGD) for surveillance of Barrett's esophagus (BE) were imaged with the SECM endoscopic probe. The device had a diameter of 7 mm, a length of 2 m, and a rapid-exchange guide wire provision for esophageal placement. During EGD, the distal portion of the esophagus of each patient was sprayed with 2.5% acetic acid to enhance nuclear contrast. The SECM endoscopic probe was then introduced over the guide wire to the distal esophagus and large-area confocal images were obtained by helically scanning the optics within the SECM probe. RESULTS: Large area confocal images of the distal esophagus (image length = 4.3-10 cm; image width = 2.2 cm) were rapidly acquired at a rate of ∼9 mm2 /second, resulting in short procedural times (1.8-4 minutes). SECM enabled the visualization of clinically relevant architectural and cellular features of the proximal stomach and normal and diseased esophagus, including squamous cell nuclei, BE glands, and goblet cells. CONCLUSIONS: This study demonstrates that comprehensive spectrally encoded confocal endomicroscopy is feasible and can be used to visualize architectural and cellular microscopic features from large segments of the distal esophagus at the gastroesophageal junction. By providing microscopic images that are less subject to sampling error, this technology may find utility in guiding biopsy and planning and assessing endoscopic therapy. Lasers Surg. Med. 49:233-239, 2017. © 2016 Wiley Periodicals, Inc.

Spectrally encoded confocal microscopy for diagnosing breast cancer in excision and margin specimens.

A large percentage of breast cancer patients treated with breast conserving surgery need to undergo multiple surgeries due to positive margins found during post-operative margin assessment. Carcinomas could be removed completely during the initial surgery and additional surgery avoided if positive margins can be determined intraoperatively. Spectrally encoded confocal microscopy (SECM) is a high-speed reflectance confocal microscopy technology that has a potential to rapidly image the entire surgical margin at subcellular resolution and accurately determine margin status intraoperatively. In this study, in order to test the feasibility of using SECM for intraoperative margin assessment, we have evaluated the diagnostic accuracy of SECM for detecting various types of breast cancers. Forty-six surgically removed breast specimens were imaged with an SECM system. Side-by-side comparison between SECM and histologic images showed that SECM images can visualize key histomorphologic patterns of normal/benign and malignant breast tissues. Small (500 µm × 500 µm) spatially registered SECM and histologic images (n=124 for each) were diagnosed independently by three pathologists with expertise in breast pathology. Diagnostic accuracy of SECM for determining malignant tissues was high, average sensitivity of 0.91, specificity of 0.93, positive predictive value of 0.95, and negative predictive value of 0.87. Intra-observer agreement and inter-observer agreement for SECM were also high, 0.87 and 0.84, respectively. Results from this study suggest that SECM may be developed into an intraoperative margin assessment tool for guiding breast cancer excisions.

Laser Dynamic Control of the Thermal Emissivity of a Planar Cavity Structure Based on a Phase-Change Material.

Tailoring the thermal emission of a material in the long-wave infrared (IR) range of 8-13 µm is crucial for many IR-adaptive applications, including personal thermal management, IR camouflage, and radiative cooling. Although various materials and surface structures have been proposed for these purposes, space-selective and dynamic control of their emissivity is challenging. In this study, we present a planar surface cavity structure consisting of a Ge2Sb2Te5 (GST) film on top of a thin metal reflector to modulate its emissivity by using an ultraviolet laser beam. A laser-induced phase change in GST allowed for the local control of emissivity. The average emissivity in the long-wave IR range was tunable from 0.15 to 0.77 simply by changing the laser energy deposited on the GST film. This enabled the laser printing of high-contrast emissivity patterns, which were erasable by subsequent thermal annealing. Emissivity-modulated GST cavities could be fabricated on not only rigid substrates but also flexible plastic substrates such as polyimide. The GST surface cavity was highly flexible and remained stable upon repeated bending to a curvature radius of 0.5 cm. This study provides a promising route for realizing scalable and flexible thermal emitters with tunable surface emissivity.

Multispectral Imaging with a Planar Cavity-Type Metasurface for Optical Security.

Multispectral imaging refers to capturing images in different wavelength ranges across the electromagnetic spectrum. Despite the potential impact of multispectral imaging, its widespread use has been limited by the poor spectral selectivity of naturally occurring materials beyond the visible range. In this study, we present a multilayered planar cavity structure to simultaneously record mutually independent visible and infrared (IR) images on solid surfaces. The structure consists of a color control unit (CCU) and an emission control unit (ECU). The visible color of the cavity is controlled by varying the thickness of the CCU, whereas its IR emission is spatially tuned by the laser-induced phase change of a Ge2Sb2Te5 layer embedded in the ECU. Because the CCU comprises only IR lossless layers, its thickness variation has negligible influence on the emission profile. This enables different color and thermal images to be printed in a single structure. The cavity structure can be fabricated on flexible substrates (plastic and paper) as well as rigid bodies. Furthermore, the printed images remain stable against bending. This study shows that the proposed multispectral metasurface is highly promising for use in the field of optical security, such as identification, authentication, and anti-counterfeiting.

Titanium oxide nanomaterials as an electron-selective contact in silicon solar cells for photovoltaic devices.

To obtain high conversion efficiency, various carrier-selective contact structures are being applied to the silicon solar cell, and many related studies are being conducted. We conducted research on TiO2 to create an electron-selective contact structure that does not require a high-temperature process. Titanium metal was deposited using a thermal evaporator, and an additional oxidation process was conducted to form titanium oxide. The chemical compositions and phases of the titanium dioxide layers were analyzed by X-ray diffraction. The passivation effects of each titanium oxide layer were measured using the quasi-steady-state photoconductance. In this study, the layer properties were analyzed when TiO2 had a passivation effect on the silicon surface. The charge and interface defect densities of the layer were analyzed through CV measurements, and the passivation characteristics according to the TiO2 phase change were investigated. As a result, by applying optimized TiO2 layer thickness and annealing temperature conditions through the experiment for passivation to the cell-like structure, which is the structure before metal and electrode formation, an implied open-circuit voltage (iVoc) of 630 mV and an emitter saturation current density (J0) value of 60.4 fA/cm2 were confirmed.