This plenary presentation is titled Photonic lanterns: shedding new light on OCT, presented at SPIE Photonics West 2023.

We have developed a new self-propelled OCT imaging technology called retrograde Tethered Capsule Endomicroscopy (R-TCE) for colonic disease screening. We successfully demonstrated that the R-TCE device can be advanced over 1 meter in 5 swine colons in vivo. R-TCE with balloon pullback imaging enabled full circumferential OCT visualization of 95.94 % ± 0.13% of the colon wall. 3D reconstructed colon OCT images and 3D rendered flythroughs showed that R-TCE is feasible for OCT microscopic imaging of the entire colon in vivo. When translated to humans, this R-TCE technology may provide a less invasive and more efficient alternative to colonoscopy.

3D micro-printing enables the formation of complex shapes at a print resolution of tens of nanometers using two-photon lithography. Our team have explored the use of 3D micro-printing to fabricate complex optical geometries directly on the end of a fiber. In this work, we have developed a lens-in-lens design that enables in-vivo high-sensitivity fluorescence and OCT imaging through a single-fiber-based probe, with a diameter <550 microns including a protective catheter sheath. In a parallel work, we have also fabricated a side-facing OCT fiber probe (<300 microns diameter) creating an elongated Bessel beam and simultaneously correct for aberrations.

Despite the emerging market in fractional-pixel CO2 lasers to treat Genitourinary Syndrome of Menopause (GSM) in menopausal women, the effect of the laser treatment on vaginal tissue remains poorly understood. We developed an intravaginal OCT endoscope that simultaneously obtains structural and vascular information during the vaginal laser procedure. Based on the monitoring and statistical analysis of the Vaginal Epithelial Thickness (VET) and Blood Vessel Density (BVD) along with the treatment for months, laser treatment shows a positive impact on vaginal health. This system can serve as a noninvasive biopsy tool in gynecological studies.

The ability to monitor disease progression over time is critical to inform patient care and prognosis, especially in usual interstitial pneumonia (UIP), the histopathological pattern seen in idiopathic pulmonary fibrosis (IPF). HRCT is limited in resolution to detect disease changes on a microscopic level, and surgical lung biopsy (SLB) has high risk of morbidity and mortality precluding its use to assess progression. Endobronchial optical coherence tomography (EB-OCT) is a bronchoscopic, minimally-invasive, high-resolution imaging method that accurately detects microscopic ILD features and is repeatable. Here, we evaluate the utility of repeat EB-OCT for monitoring microscopic disease progression in UIP/IPF.

We demonstrated the long coherence 1.0-μm stretched-pulse mode locking wavelength-swept source based on a precise dispersion compensation using chirped fiber Bragg grating (CFBG). In the optical pulse width of 72 ps, the optical bandwidth was 97 nm, and the coherence length was 5.0 mm. We also obtained ultra-high speed in-vivo human retinal optical coherence tomography images with a 5-MHz A-line rate. Because the dispersion profile of CFBG was designed to be linear in wavenumber, the wavenumber linearity of this laser is 0.9999997 (R2), which avoided the use of interpolation during real-time imaging.

Optoretinography (ORG) is an emerging effort to noninvasively measure the functional responses of retinal neurons. We and other groups have previously shown that cellular-resolution coherent imaging of photoreceptors can reveal microscopic stimulus-evoked changes in the shape of photoreceptors. Such methods track the position of cellular features using phase differences among them. Here we present a novel method using low-cost OCT hardware that monitors the phase velocity of these features instead. The primary advantage of this system is elimination of the need to resolve and track single cells using costly and complicated optical and computational methods. This system may permit rapid, high-throughput measurement of retinal function healthy volunteers and patients.

Ophthalmic optical coherence tomography (OCT) has achieved remarkable clinical success but remains sequestered in ophthalmology specialty offices. Recently introduced robotic OCT systems seek to expand patient access but fall short of their full potential due to significant imaging workspace and motion planning restrictions. Here, we present a next-generation robotic OCT system capable of imaging in any configuration that is mechanically reachable. This system overcomes prior restrictions by eliminating fixed-base tracking components, extending robot reach, and planning alignment in six degrees of freedom. With this robotic system, we show repeatable subject imaging independent of posture under widely varying head orientations.

Phase-sensitive optoretiography is an emerging contrast method to assess the functional activity of retinal neurons in living humans. So far, functional signals were mostly observed in the photoreceptors. However, using full-field swept-source optical coherence tomography, additional signals were measured in the inner plexiform layer (IPL), which are linked to higher neuronal activity. Here, we investigated optoretinography signals for 6 different subjects and analyzed the influence of eye motionand the stability of two phase-evaluation algorithms. Thereby, photorceptor signals were observed in all and IPL signals in 85% of the measurements, with matching basic time courses and spatial signal-distribution for all subjects.

Visible light OCT requires light sources with high spatial brightness and broad spectral range. Typical solutions are based on supercontinuum generation from a short pulse. Here, we demonstrate visible light superluminescent diodes (SLDs) for OCT imaging of the human retina. SLDs are about an order-of-magnitude less costly than supercontinuum sources and have lower intrinsic excess noise, enabling imaging closer to the shot noise limit. We show that while SLDs lack continuous broadband spectra, they can provide concentrated power at specific wavelengths. Our approach enables us to image near the shot noise limit in vivo and provides novel chromophore information.

Full-field OCT systems and the use of adaptive optics have enabled high resolution, functional OCT imaging of photoreceptor cells. However, currently the technologies are limited to experimental systems. For clinical translation, clinical grade devices are needed with sufficient resolution as well as phase stability. In this talk it is shown that a slightly modified Spectralis OCT can resolve single photoreceptor cells. Furthermore, algorithms for the correction of motion induced artifacts will be introduced and discussed, as well as approaches for correcting for the respective phase errors in scanning OCT.

We present the first dynamic full field optical coherence tomography (D-FFOCT) independent module which can be easily integrated into any commercial microscope. Combining the whole setup with a commercial incubator,, we demonstrate three-dimensional live imaging experiments over time periods of minutes to hours to days keeping the sample in healthy conditions. We show timelapse high resolution live images of retinal explants and organoids in disease modeling applications.

Optical coherence tomography (OCT) revolutionized diagnostics in ophthalmology. Traditional OCT assumes static subjects and produces artifacts during motion. Robotically-aligned OCT mitigates these artifacts via hardware motion compensation. However, hardware imperfections result in residual motion error. Here we present a digital motion correction approach where we utilize synchronized sensing of the pupil and scanner components to measure the state of the imaging process over time. We subsequently map each A-scan to its corresponding location in the volume given sensor data during its acquisition. We demonstrate our correction in human imaging and observed 68% reduction in maximum residual axial error.

Retinal capillary blood flow speeds quantification may provide biomarkers for retinal diseases. While OCTA visualizes the retinal vasculature, it provides limited information about the blood flow speeds. We present an OCTA-based method for measuring quantitative surrogate markers for blood flow speeds in retinal capillaries using a temporal autocorrelation decay model, by acquiring multiple OCT B-scan repeats and compiling OCTA measurements both spatially and temporally. A 600 kHz swept light source enabled short and multiple interscan times with fine A-scan spacing. We show blood flow speed differences among retinal vascular plexuses in healthy eyes and alterations in eyes with diabetic retinopathy.

Here, we demonstrate the visual evoked blood flow change in trilaminar retinal vasculature in rodents using OCT capillary velocimetry. A custom-built spectral-domain optical coherence tomography operates on 800 nm region performed all the imaging. In-vivo measurements were conducted on dark-adapted Brown Norway rats. The retinal blood flow velocity was calculated using a modified dynamic light scattering (DLS) – OCT method. As a result, the blood flow velocity in arterioles, venules, and capillaries in the retinal vasculature can be resolved. Flicker stimulation triggered heterogeneous responses – reduced flow velocity in large vessels vs. increased flow velocity in capillaries.

While Doppler OCT is effective at measuring axial velocities, OCT autocorrelation was introduced to measure flow in all directions. However, accuracy is limited as several factors other than particle velocity including diffusion, blood-cell tumbling, and axial velocity gradient affect signal decorrelation. Here, we show that the use of the ratio of autocorrelation from few-mode optical coherence tomography (FM-OCT) improves the accuracy of transverse flow velocity measurements. To validate our approach, we showed that milk velocity pumped through a circular tube at constant speed was accurately retrieved.

Aging and myopia are associated with changes in the biomechanical properties of vitreous, inducing fibrous liquefaction. Characterizing vitreous dynamics (rheology) during eye movements can provide a better understanding of biophysical changes in vitreous with disease, as well as provide a quantifiable clinical index of changes from both aging and myopia. Highly sensitive detection of the scattered light intensity in the eye and micrometer image resolution represent advantages of SS-OCT over other technologies to image vitreous. This investigation aims to characterize vitreous dynamics during eye movement. Specifically, we describe a technique for in vivo measurement of vitreous movement tracked over time using high-speed SS-OCT imaging. We also introduce velocimetry analysis of volumetric OCT data sets, enabling the characterization of velocity distributions of vitreous opacities in emmetropic and myopic eyes during horizontal saccades. In vivo imaging was performed with a prototype SS-OCT instrument. We use a manual tracking analysis method to extract velocimetry information on vitreous movement from in vivo data. The velocity of floaters in the vitreous was established by tracking their movement over time, resulting in the hypothesis that the vitreous is more liquid due to the age at which the floaters move faster.

A framework presented in this study demonstrates the ability of pressure sensors to aid in acquiring reliable OCT/OCTA images. A handheld OCT probe combined with a disposable attachment with built-in force sensors was developed and its potential for skin imaging was demonstrated. With the real-time pressure monitoring, an operator can easily determine whether the pressure applied to the skin is below the threshold of affecting OCT imaging and uniform so as to obtain repeatable OCTA images.

Hereditary Hemorrhagic Telangiectasia (HHT) is an inherited, autosomal dominant, vascular disorder that affects an estimated 1 in 5,000 individuals (approximately 1.5M globally and 62,000 in the USA. It is characterized by the presence of multiple arteriovenous malformations (AVMs). An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels connecting arteries and veins, disrupting normal blood flow and oxygen circulation. This study proposes a high-resolution, non-invasive multifunctional imaging system that combines 1.7um D-OCT/OCTA to accurately interrogate HHT skin lesions, including hands, chest, and tongue. Integrated OCTA and Doppler OCT imaging can provide information on lesion architecture and microvasculature. We use this methodology to interrogate individual lesion morphology, compare mucosal and skin lesions, and ultimately, evaluate the vascular effects of anti-VEGF treatment.

A 32-channel CR-OCT system was developed to facilitate a data-efficient acquisition of three-dimensional imaging data in laparoscopy. The system consists of a frequency comb source, a high-power doped-fiber optical amplifier, an all fiber-based, 32-channel interferometer, a 32-beam MEMs-based forward-looking 2D laparoscopic probe, and 32-channel detection channels. A novel phase and polarization modulation circuit was included to allow complex and polarization-resolved fringe detection. The system operated at an effective A-line of 10 MHz. We demonstrate video-rate volumetric CR-OCT imaging of a patterned sample and polarization-sensitive imaging of ex vivo tissues.

Optical coherence tomography (OCT) has wide application in medicine, particularly ophthalmology. In the anterior chamber of the eye, OCT can potentially image blood cells to monitor cellular response to injury or inflammation. However, low volumetric refresh rates limit OCT in applications that require the tracking of individual, moving cells. Therefore, we propose an efficient 3D cell tracking using adaptive scanning OCT. Adaptive scanning prioritizes capturing regions of interest that change from volume to volume. Using depth information from OCT A-scans, our cell tracking method successfully localized simulated cells across multiple OCT volumes.

Digital refocusing of optical coherence tomography (OCT) restores the spatial resolution degraded by defocusing. To apply this to imaging of biological tissue with point-scan Fourier domain OCT (FD-OCT), fast volume acquisition is needed to prevent motion disturbance. This study demonstrates the Lissajous-cycle-wise (LCW) digital refocusing algorithm applied to in vivo imaging at acquisition rates typical of FD-OCT. Blurring along and perpendicular to the scanning direction are compensated by inverse filtering and compositing A-lines of different scanning directions after motion correction, respectively. Ex vivo and in vivo biological sample experiments are applied for the proof of concept. The blurred images due to defocusing are sharpened by the LCW digital refocus algorithm.

Conventional optical lenses are usually used in OCT systems to perform high lateral resolution imaging. However, the Gaussian beam profile typically used in OCT links the depth of focus (DOF) to the lateral resolution. We have experimentally shown that using a cascade system of an ultrasonic virtual tunable optical waveguide (UVTOW) and a short focal-length lens can provide a large DOF without severely compromising the lateral resolution compared to an external lens with the same effective focal length. We demonstrate the tunability of the focal length that this system offers without any need for mechanical perturbation to the imaging setup.

In our study, we simulate aberration-diverse optical coherence tomography (AD-OCT) by coherently averaging astigmatic beams of different angles to investigate its capacity to improve imaging performance at large depths relative to a Gaussian control beam. We find that AD-OCT provides the greatest improvement for small numerical apertures (NA = 0.10) but only marginal improvement for larger numerical apertures (NA = 0.25). Optimal astigmatic foci separation was found to decrease as NA increased, and less than 10 states were required to see maximal improvement. These results suggest that AD-OCT improves imaging quality over conventional Gaussian-beam OCT for low NA systems after averaging just a few states.

Full-field swept-source optical coherence tomography (FF-SS-OCT) presents promising capabilities, particularly for ophthalmic imaging. One current limitation is that the extent of the field of view is limited by safety considerations due to the laser focused in front of the eye. Another limitation is that speckle-noise decreases the quality of images. We here used a diffuser that serves the dual purpose of increasing the size of the laser hot spot and reducing speckle-noise. We show that speckle-noise in OCT images can be reduced when moving the diffuser and averaging multiple volumes.

Traditionally, line scan OCT (LS-OCT) systems use a cylindrical lens to generate a line-shaped beam with Gaussian intensity illumination along the line, which leads to spatially-dependent signal-to-noise ratio (SNR) distribution of the OCT system along the B-scan direction. A novel, Powell lens-based LS-OCT (PL-LS-OCT) system was designed for uniform intensity illumination along the B-scan direction. The PL-LS-OCT can generate images with ~ 2 μm × 1.7 μm (lateral × axial) resolution in free space at image acquisition rate of and 4,500 fps. Images of biological tissues were acquired with the PL-LS-OCT system.

Time-stepped optical frequency comb (TSOFC) sources have extended the imaging capabilities of optical coherence tomography (OCT). However, existing TSOFC laser architectures have significant limitations in cost, complexity, and performance. A recently developed active integrated photonic circuit platform – lithium niobate-on-insulator (LNOI) – has the potential to address these limitations. We designed and fabricated custom LNOI integrated photonic circuits and demonstrated LNOI-based TSOFC sources for OCT. The fabricated LNOI photonic chips support optical frequency switching at the 1 ns time-scale, although the current laser prototypes are limited by the driving electronics to switching times of several hundred nanoseconds.

This study’s goal is to apply Denoising Predictive Coding (DN-PC), a novel compressed sensing (CS) algorithm for reconstruction of optical coherence tomography (OCT) images of breast tissue. We have assembled an image bank of representative OCT samples of normal breast and breast cancer tissue. We apply DN-PC for compression at decreasing a-line sampling rates to evaluate a relation between reconstruction behavior and image features of breast tissue as well as compare to classic downsampling and interpolation-based methods.

Functional extensions of Optical Coherence Tomography (OCT) stand to enhance the value of structural imaging for clinical applications. Polarization sensitive (PS-) OCT and attenuation coefficient imaging provide complementary information useful for interrogating complex tissue microenvironments such as atherosclerotic plaques. However, additional hardware for generating two input polarization states, and enabling angular-diverse measurements, is necessary to fully exploit these two respective techniques. We present a platform for simultaneous, depth-multiplexed acquisition of PS- and angular diverse data, expanding prior methods for fiber-based PS-OCT and aperture-based numerical aperture (NA) multiplexing, and demonstrate its utility in discriminating plaque components in human coronary arteries.

Phase-sensitive optical coherence tomography (OCT) enables label-free imaging of structural dynamics with nanoscopic sensitivity. However, the inevitable bulk tissue motions degrade the signal stability and introduce extra phase error. To suppress the motion-induced phase error, we propose a phase-restoring subpixel motion correction method for post-hoc motion correction in Fourier domain OCT, which enables translational shifts of complex-valued OCT images by arbitrary distance. Phantom and in-vivo rodent optoretinogram imaging experiments were conducted to demonstrate the advantages of the proposed method over conventional pixel-level method and the Fourier transform based method.

A multimodal approach for margin assessment combines fast, cross-sectional imaging using 1050 nm spectral-domain optical coherence tomography (SD-OCT), offering sensitivity to highly-scattering malignant tissues, with complementary sub-cellular resolution and molecular specificity provided by ultraviolet photoacoustic remote sensing virtual histology. The interferometric synthetic aperture microscopy (ISAM) extension to OCT was implemented to achieve spatially-invariant lateral resolution, reducing the resolution disparity between each modality by avoiding numerical aperture trade-offs. System validation included carbon fiber and TiO2 particle phantom imaging, and ex vivo biological imaging was demonstrated in fresh, thick murine tissues, and benign and malignant human breast samples.

In this work, we developed a methodology to non-invasively quantify total hemoglobin [tHb] concentrations in the microcirculation of the skin with visible-light spectroscopic optical coherence tomography (vis-sOCT). Our approach is based on the spatial distribution of [tHb] inside a vis-sOCT scan. Local [tHb] are retrieved by analyzing the optical density at each point of the tomogram. We show that the [tHb] distribution map, termed hemogram, presents blood vessel distributions comparable to that of optical coherence tomography angiography. In addition, we obtain a clinically useful measurement of the average [tHb] by analyzing the [tHb] across the hemogram. For a healthy volunteer, this average [tHb] of 11.62 g/dL falls within the expected clinical range and is consistent between eight independent measurement locations on the skin with a standard deviation of 0.88 g/dL.

Optical coherence tomography (OCT) has been a powerful 3D optical imaging tool in the last decade while it lacks molecular information. In this work, we integrate the mid-infrared photothermal microscopy with the OCT approach to demonstrate a bond-selective full-field optical coherence tomography (BS-FF-OCT), in which a pulsed mid-infrared laser is used to modulate the full-field OCT signal through the photothermal effect. This method achieves label-free volumetric infrared spectroscopic imaging at 1-μm isotropic resolution, demonstrated by a variety of samples, including 1 μm PMMA beads embedded in agarose gel, polypropylene fiber mattress, myelinated nerve bundle in mouse brain tissue, Caenorhabditis elegans, and cancer cell spheroids.

OCT is a non-contact interferometric imaging modality, which allows, next to visualization, quantification of tissue optical properties, yielding desired information about structure and organization of tissue. To date, no rigorous and standardized means for computing the precision of OCT-derived optical tissue properties has been proposed. Here, in our investigation, we develop a theoretical framework providing the lower bound for the precision of OCT-derived attenuation coefficients. Furthermore, in order to ensure clinical relevance of our framework, we derive and validate an analytical equation for this lower bound, providing a fast, rigorous and easy-to-use approach for commonly used OCT systems.

A new deep-learning-based scatterer density estimator (SDE) is demonstrated. The SDE is trained by pairs of numerically simulated OCT images and its background parameters including the scatterer density, resolutions, and signal-to-noise ratio. For this simulation, we introduced a new noise model that accurately accounts for the spatial properties of three noise types: shot, relative-intensity, and detector noise. This SDE was experimentally validated by phantom and in-vitro tumor spheroid measurements. Significantly improved accuracy was found in comparison to our old SDE being trained with a naïve noise model that does not account for the spatial noise property.

Asthma is a chronic inflammatory disease associated with thickening of the airway smooth muscle (ASM). Currently, there is no imaging modality available to assess ASM mass in vivo, other than invasive biopsies. Polarization Sensitive Optical Coherence Tomography (PS-OCT) might enable minimally invasive in vivo quantification of ASM mass, by providing birefringent tissue-specific contrast. We performed in vivo PS-OCT in three asthma patients who underwent bronchial thermoplasty (BT), an endoscopic treatment which induces ASM reduction. We found an excellent correlation between ASM content in PS-OCT images and biopsies. Moreover, PS-OCT was able to detect a reduction in the ASM content after BT.

Birefringence of the retinal nerve fiber has the potential as a useful biomarker for the study of neurodegenerative diseases such as multiple sclerosis. To realize this potential and assist in the development of diagnostic tools and therapies for neurodegenerative diseases, high-resolution retinal polarimetry suitable for humans and rodent models is needed. However, conventional polarization-sensitive optical coherence tomography (PS-OCT) processing generally imposes a resolution penalty by spatially filtering incoherent Stokes vectors, or the underlying coherent Jones-based OCT measurements. Here, we demonstrate the possibility to resolve polarimetric parameters of individual axonal bundles in-vivo with our probabilistic non-local means processing for Stokes-based PS-OCT.

Endobronchial polarization sensitive optical coherence tomography (PS-OCT) provides high-resolution images and can detect tissue birefringence. Using collagen birefringent properties, we postulated that PS-OCT can detect and quantify pulmonary fibrosis in interstitial lung disease (ILD) patients. In this study, we demonstrated PS-OCT in 19 patients (16 ILD and 3 non-fibrotic controls). In-vivo PS-OCT was performed by advancing a distal scanning endoscope through the working channel of a bronchoscope to the lung periphery of the patients. Results show that PS-OCT is feasible, safe, and can quantify pulmonary fibrosis, thereby has potential as minimally invasive diagnostic tool to detect fibrotic progression in ILD.

Despite promise in early pilot studies, clinical translation of intravascular PS-OCT has been limited by the complexity of incorporating polarization modulation. We present a signal processing pipeline which uses maximum-likelihood estimation to reconstruct the polarization properties of tissue measured with a single input polarization state (SIPS-OCT), enabling polarization-sensitivity with existing intravascular OCT devices. SIPS-OCT estimates both the depth resolved birefringence and optic axis orientation, with excellent qualitative and quantitative comparisons to conventional dual-input state PS-OCT. These results present an encouraging step towards removing barriers to PS-OCT adoption by enabling polarization-sensitivity in existing intravascular OCT systems.

Polarization-sensitive OCT (PS-OCT) derives image contrast from tissue birefringence. Here, we introduced triple-input polarization sensitive optical coherence tomography (TRIPS-OCT), a new polarimetric modulation and reconstruction strategy for depth-resolved tomographic birefringence imaging in-vivo. We modulated the polarization states between three repeated frames and enabled the reconstruction of the Mueller matrix at each location within the triple-measured frames. We demonstrated a 2-fold reduction of the birefringence noise floor compared to the conventional dual-input reconstruction method, and a 3-fold reduction of the measurement error of optic axis orientation in retinal imaging with the compensation of corneal retardance and diattenuation.

Quantitative micro-elastography (QME) is a compression-based optical coherence elastography technique that visualizes micro-scale tissue stiffness. Current benchtop QME shows great potential for identifying cancer in excised breast tissue (96% diagnostic accuracy), but cannot image cancer directly in the patients. We present the development of a handheld QME probe to directly image the surgical cavity in vivo during breast-conserving surgery (BCS) and a preliminary clinical demonstration. The results from 21 patients indicate that in vivo QME can identify residual cancer based on the elevated stiffness by directly imaging the surgical cavity, potentially contributing to a more complete cancer excision during BCS.

Existing conventional OCT systems lack the ability to robustly measure biomechanical contrast. While many wave-based elastography methods have been developed for imaging stiffness, they also have limitations that make adaptation to imaging in vivo infeasible. While passive elastography doesn’t require coherence, we also cannot derive quantitative mechanical properties without it. Similarly, it been assumed that reverberant elastography also requires coherence. However, through benchtop raster-scanning and balloon catheter radially-scanning OCT, we demonstrate that it is possible to adapt reverberant elastography for unsynchronized, free-running excitation to obtain cross-sectional shear wave elastography at speeds compatible with in vivo applications.

Strain retrieval from maps of displacement due to mechanical loading is central to optical coherence elsatography. However, displacement data is usually highly oscillatory since it is derived from the phase difference between OCT images. Oscillations limit sensitivity and signal to noise ratio of retrieved strain. We present an alternative approach to strain retrieval that does not use phase difference, but determines the unique spectral domain transformation that maps the unloaded A-scan to the loaded A-scan, exactly, for regions of constant strain. Our novel method of strain retrieval has a higher sensitivity and signal to noise ratio than existing approaches.

Full-field optical coherence tomography (FF-OCT) enables high-resolution 3D imaging. FF-OCT is a noninvasive and label-free imaging technique that produces high-resolution microscopy images of scattering biological samples. During the last decade, FF-OCT has become invaluable for many biomedical applications. It requires the extraction of the amplitude and phase components from the interference signal, for which a phase-shifting algorithm is usually used. However, this algorithm is not well adapted for real-time observation of in-vivo samples, therefore limiting the use of FF-OCT for ¬in-vivo imaging and clinical transfer. We propose in this study a new approach in FF-OCT that enables single-shot acquisitions using off-axis digital holography principle with low spatially and temporally coherent source.

Optical coherence tomography (OCT) reveals microstructure of biological tissue by measuring the pathlength difference of backscattered light at micron-scale resolution and millimeter-scale depth of penetration. Speckle grains, with a size corresponding to the spatial resolution of the OCT system, complicate the identification of tissue morphology and obscure subtle differences in tissue scattering properties. There is a need for a physics-based approach to generate standardized ground truth for OCT speckle suppression processing algorithms. Here we demonstrate an angular compounding system using sample tilting in combination with a model-based affine transformations to generate physically derived speckle suppressed ground truth data.

Recently, time-domain full-field OCT (TD-FF-OCT) evolved into the tool for in vivo eye exploration. Particular benefits of TD-FF-OCT include cellular resolution, rapid en face imaging without scanning artifacts, reduced sensitivity to optical aberrations, and non-contact performance. One limitation of TD-FF-OCT is related to its ’time-domain’ nature – tomographic image is reconstructed from several consecutive (in time) camera frames. The sample should stay static, otherwise the signal is reduced. In this work we present TD-FF-OCT that can capture in vivo human corneal images in a single camera shot. This became possible by using a combination of optical/image processing and deep learning techniques.

In this work, we propose to utilize an end-to-end deep learning approach for the reconstruction of structural OCT images based on the rich information contained in raw OCT data alone instead of performing signal processing with manual tuning of the associated system parameters. The proposed deep learning approach already yields promising results on a small training data set of widefield OCT images. Qualitative results suggest that the neural network is able to implicitly learn the full signal processing pipeline and its inherent system parameters but is strongly impacted by the data variability seen during training.

Mechanical properties of cells and extracellular matrix play important roles in the regulation of various biological processes such as gene expression, adhesion, and migration of cells. However, it is challenging to map three-dimensional (3D) elasticity on the micro-scale using existing techniques. We propose subcellular mechano-microscopy, a variant of compression-based optical coherence elastography, for 3D elastography of cell spheroids with isotropic elasticity resolution of 10 µm, over large fields of view covering multiple spheroids. We use the proposed technique to scan multicellular non-metastatic breast cancer cell spheroids embedded in gelatin methacryloyl (GelMA) hydrogels and co-register the micro-elastograms with fluorescence microscopy images.

We demonstrate high-resolution (3.8-µm axial and 4.8-µm lateral) three-dimensional dynamic (D-) OCT imaging by 840-nm spectral domain OCT, and compare it with a low-resolution 1.3-µm D-OCT. The D-OCT images are obtained by logarithmic-intensity-variance method, which is sensitive to the magnitude of signal fluctuation. Human-induced-pluripotent-stem-cell derived alveolar (lung) organoids and human breast cancer (MCF-7) spheroids were examined. The high-resolution D-OCT revealed the tessellation of high and low dynamics at the matured alveolar epithelium. It is also found that such matured alveolar epithelium exhibits ragged inner surface. For the spheroids, high-scattering spots with low dynamics were observed only in the high-resolution image.

We present interface self-referencing D-FF-OCT (iSR-D-FF-OCT), a new dynamic full-field optical coherence tomography (D-FF-OCT) imaging technique, which is self-referenced, vibration-insensitive and overcomes D-FF-OCT fringe artefact limitations near specular surfaces. iSR-(D)-FF-OCT complements and is easily implemented on existing D-FF-OCT set-ups to cover a zero to several hundred micrometer depth range. iSR-(D)-FF-OCT has a homogeneous contrast across the imaging field enabling flawless mosaicking. In fibroblasts, retinal organoids, and corneal explants, we demonstrate imaging in the vicinity of reflective interfaces without fringe artefacts, in a live, label-free, non-invasive manner with sub-diffraction limited sectioning capacity within 3D samples.

Longitudinal imaging of live organisms is essential to life science research aiming to understand biological processes. Recently, the imaging system has been housed for longitudinal imaging by mounting the optical imaging system in an incubator, while facing the limitations of single-modality and low throughput. Here, we proposed the OCToScope, a multi-modal, high-throughput and compact platform that is compatible with commercial incubators. OCToScope incorporates Optical Coherence Tomography(OCT) to achieve non-invasive three-dimensional imaging, and fluorescent imaging that retrieves cell-specific information. OCToScope also supports automatic scanning of mass samples quantity with motorized x-y-z stage and perform high time-resolution imaging for long-term studies. we used OCToScope to provide a systematic and comprehensive characterization of human heart organoids for over 30 days without any interference.

For this study, we developed a multi-modal functional retinal imaging system for small animal models to investigate representative AMD mice models. The system can simultaneously acquire information on melanin concentration, lipofuscin accumulation, and choriocapillaris. The newly developed system is expected to provide multilateral perspectives for further studies in AMD, enabling vision scientists to investigate the correlations between melanin, lipofuscin, and choriocapillaris for the root cause of the disease.

Tissue metabolism is an inter-and intra-cellular process, which is essential to maintain the living state of tissue. Functional abnormality of such cellular processes initiates several metabolic diseases including non-alcoholic-fatty-liver-disease (NAFLD), liver fibrosis, cancer, chronic kidney disease, and so on. To understand the metabolic processes and how tissue metabolism changes from healthy to diseased conditions, it is required to investigate tissue metabolic activity in animal models in a label-free manner. Since the metabolic structures in animal organs extend into the deep region, deep tissue metabolism imaging is necessary. In this paper, we demonstrate the investigation of ex vivo animal organ models’ metabolism including mouse liver and kidney tissues using OCT-based dynamics imaging method. The dynamics imaging method is based on logarithmic intensity variance (LIV) analysis that enables volumetric metabolic imaging with a 50-kHz swept-source OCT system. NAFLD model mouse livers and obstructed mouse kidney model were investigated ex vivo. In the normal liver, highly dynamic vessel-like structures were observed and they might correspond to high metabolic activity in the periportal/perivenous zones. In the 1-week NAFLD model, a macroscopic, ring-shaped dynamic structure was observed which may indicate highly-motile lipid droplets. In the 2-week NAFLD model, highly-dynamic fragmented vessel-like structures were observed, which are believed to correspond to inflammatory cells around large vessels. In the normal mouse kidney, superficial pipe-like metabolic structures were observed that may correspond to the kidney renal tubules. The pipe-like structures did not appear in the obstructed kidney model.

We construct a universal image formation theory that generalized individual optical imaging systems including OCT by stepping up to the four-dimensional (4-D) coordinate system. We show how the unified image formation theory is formulated by applying the modern physics to imaging systems. A bird’s-eye view from the four dimensions brightens up the perspective of the image formations in almost all optical systems simultaneously, even though different types of imaging systems seem entirely distinct and unrelated. We define a 4-D aperture in the 4-D frequency domain as an instrumental function that indicates a spatial-temporal resolution, which allows for the comparison of 4-D optical resolution in all imaging systems that includes a time response stemming from the light-matter interaction. In virtue of a strict definition of a 4-D frequency cutoff, the optical resolution can be evaluated and compared to other imaging systems in the frequency domain more clearly than in the real-space domain. The unification of individual imaging systems has been achieved with the 4-D aperture. It can easily be visualized how the 4-D aperture captures a certain region in an object frequency, and how the image formation is performed with the captured 4-D frequency region by stepping down to the 3-D frequency domain. We will show that some types exist in terms of the image formation, which means that how to drop one dimension to form the 3-D image depends on the optical system. We will find that our new framework can explain each individual existing approach.

Cancers is one of the most fatal diseases threatening the survival rate of humans. The recent advances in the cell culture methods allow cultivation of human-derived tumor cells as a 3-D culture, so-called tumor spheroid, which closely emulates the in vivo solid tumors. Hence, it can be used for anti-cancer drug testing, where the efficacy of anti-cancer drugs is evaluated by the drug-induced morphological and viability alterations of the spheroids. The morphological and tissue viability alterations can be evaluated by using staining histology, bright field microscopy, and fluorescence microscopy. However, these methods have several limitations. First, most of them use chemical labeling and/or tissue slicing, and hence, they are invasive. Second, they are 2-D methods. And hence, volumetric morphology, such as alteration of spheroid volume, cannot be evaluated. Third, their penetration-depth is limited to a few hundred microns. It prevents the imaging of thick tissues, such as spheroid. To overcome the above mentioned limitations, we developed a completely label-free 3-D dynamic optical coherence tomography (D-OCT) method for intracellular motility evaluation of tumor spheroid. To validate the utility of our D-OCT method, we organized several studies, including time-course and drug-response evaluations of human breast cancer (MCF-7 cell-line) spheroids. The 3-D morphological and cell viability alterations of MCF-7 spheroid during time-course and under the application of several anti-cancer drugs have been successfully visualized and quantified using D-OCT. The results suggest that D-OCT might be a useful for tumor spheroid-based drug testing and it might be a useful tool for precision medicine research.

Differential interference microscopy (DIC) is a method to obtain the refractive index distribution of a sample as contrast. It is suitable for biological cells, however, DIC can only obtain 2D images from thin samples. Therefore, we introduce a new imaging method, volumetric differential contrast (VDC) imaging using optical coherence tomography (OCT). This method enables getting 3D differential contrast of thick samples. VDC was designed based on the disperse scatterer model (DSM), a new theoretical model of OCT, and obtains differential contrast by complex numerical processing of OCT signal. DSM represents the sample as a spatially distributed refractive index with dispersed random scatterers, and OCT signal was formulated from this model. VDC uses two complex OCT signals, s1 and s2 at two laterally slightly distant positions, and the final image is defined as Im[s1 s2. This signal forms a spatially differential image of the product of the refractive index distribution and the scatterer density. According to the formulation, the size of the differentiation kernel, corresponding to the shear amount of DIC, is proportional to the defocus of the probe beam and the separation between s1 and s2. This method was validated by an in vitro spheroid sample and an in vivo zebrafish sample, measured by spectral domain OCT with a center wavelength of 830 nm. VDC images were obtained from refocused and defocused signals.

This paper aims at introducing a speculative (philosophical) framework to comprehend modern metrology. In classical sense, measurement measures physically existing quantities, such as length, mass, and time. In contrary, modern measurement measures a wide spectrum of objects-to-be-measured, such as imaging biomarker, which is user-defined patterns. Artificial-intelligence (AI-) based diagnosis is another example. If we regard an optical coherence tomography (OCT) device equipped with the diagnostic AI as a comprehensive “measurement system,” the object being measured by this system is a “disease,” which is not a physical quantity but a concept. To comprehend the wide range of modern measurements, we introduce a speculative (philosophical and theoretical) model, so-called “epistemological-metrology model.” In this model, the act of measurement is described as a cascading encoding and decoding processes. In the encoding processes, three types of objects-to-be measured are considered. They include the substance, existence, and concept. The acts of measurements are then classified into “sensing,” “understanding,” and “reasoning,” which measure to the substance, existence, and the concept, respectively. We point out that, the measurements in the understanding and reasoning classes are constructive. Namely, they proactively define the quantity-to-be-measured by the measurement modalities themselves. A speculative method to warrant the relevance of such constructive measurements is presented. Several modern OCT-related measurements, including AI-based diagnosis, some types of polarization sensitive OCT, and attenuation coefficient imaging are investigated by using this this theoretical framework.

Optical biometers are routinely used to measure intraocular distances in ophthalmic applications such as cataract surgery planning. However, due to their high cost and reduced transportability, access to them is still limited in low-resource and remote settings, where the prevalence of cataract is higher. To increase patients’ access to optical biometry we propose a novel low-cost frequency-domain optical delay line (FDODL) based on a stepper motor spinning a tilted mirror, integrated into a time-domain (TD) optical coherence tomography (OCT) system. Optical simulations of the low-cost FDODL demonstrated its capability of axially scanning different ranges simply by selecting different tilt angles of the spinning mirror with respect to the motor shaft direction, without any changes to the motor itself. Considering off-the-shelf components up to 2-inch in aperture and a tilt of 5 mechanical degrees, the optical pathlength range could reach up to 26.63 mm. A prototype of the low-cost FDODL with a 1.5-degree tilt angle and an A-scan frequency of 10 Hz was experimentally implemented and combined with a TD-OCT system. The scanning capability of the system was characterized to be 7.31 mm, in good agreement with the results of the simulation. The TD-OCT sample arm featured a fixed delay unit with two orthogonally polarized sample beams, focusing on the anterior segment and on the retina, respectively. The intraocular distances of a model eye were measured with the proposed low-cost biometer and found in agreement with the manufacturer’s specs, validating our novel design.

We present a novel mouse eye imaging system based on the Spatio-Temporal Optical Coherence Tomography (STOC-T) technique capable of acquiring structural image of a mouse retina at a volumetric rate of 112 Hz. A fundus camera and white light illumination aid the alignment of the mouse and the adjustment of the focal plane in the mouse retina for the STOC-T image. The fundus camera is calibrated so that when the white-light image of the mouse eye fundus appears in focus after the appropriate gel thickness is selected for a given mouse and bi-concave lens, the corresponding near infrared STOC-T image of the photoreceptor layer is also in focus, albeit with minor shifts. We present images of retinal and choroidal tissue from a B6 albino wild type mouse after the focal plane adjustment with richness of details.