This PDF file contains the front matter associated with SPIE Proceedings Volume 11948, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Thinning of the outer nuclear layer (ONL) is an important pathological feature and possible biomarker of age-related macular degeneration (AMD). The demarcation of the ONL and Henle’s fiber layer (HFL) is visually unattainable with standard optical coherence tomography (OCT) imaging. In this work, we built a volumetric directional OCT prototype which constitutes two optical scanners in the sample arm that synchronously scan the imaging beam on the pupil and retina. The imaging beam’s entry positions and incident angles on the pupil and retina respectively are precisely controlled and optimally maintained to generate sufficient contrast of the HFL over the entire macular volume.

Optical coherence tomography (OCT) is a medical imaging modality that can be used to quantify microstructural parameters of human kidneys in the cross-sectional view for kidney transplant surgeries to identify the organ’s health status. Existing desktop OCT devices suffer from limited scan area; therefore, it is difficult to evaluate the entire kidney. We explore the feasibility of combining the OCT system with a 7 degree-of-freedom robotic manipulator to leverage the robot’s large workspace and high localization accuracy for wider scan area and precise tracking of the OCT probe. With the proposed robotic-OCT procedure, the tissue sample can be detected using an RGB-depth camera for OCT scan path generation and scanned with online probe height optimization. A feasibility study was carried out by scanning an ex-vivo porcine kidney with the robotic-OCT system. Results show that over 38% of the tissue can be scanned. The tissue surface anatomy can be correctly reflected in 3D OCT image stitching; The online probe height optimization is able to maintain a constant distance between the probe and the tissue surface.

Optical coherence tomography (OCT) is a high-resolution imaging technique that provides wide field and high-speed imaging of three-dimensional volume. Stretched-pulse mode-locked (SPML) wavelength-swept laser has recently emerged as a promising ultrahigh-speed wavelength-swept laser that provides an A-line rate up to tens of MHz. The SPML laser utilizes chromatic dispersion to generate the wavelength-swept output with repetition rates from a few megahertz to over 10 MHz without using any mechanical wavelength scanning filter. For a simple and compact SPML laser design, utilization of a few meter-long chirped fiber Bragg grating (CFBG) as the intra-cavity dispersion element is recently demonstrated. In this work, we present SPML wavelength-swept laser using intra- and extra-cavity CFBG for the ultrahigh-speed OCT. We investigated the performance of the SPML laser as a light source for the ultrahigh-speed OCT by utilizing a combination of intra and extra-cavity stretching. We present that the noise performance and the coherence length performance of the laser can be adjusted and optimized through a proper combination of the intra and the extra cavity stretching in the SPML laser.

Optical coherence tomography (OCT) has evolved into a powerful imaging technique that allows high-resolution visualization of biological tissues. However, most in vivo OCT systems for real-time volumetric (3D) imaging suffer from image distortion due to motion artifacts induced by involuntary and physiological movements of the living tissue, such as the eye that is constantly in motion.While several methods have been proposed to account for and remove motion artifacts during OCT imaging of the retina, fewer works have focused on motion-compensated OCT-based measurements of the cornea. Here, we propose an OCT system for volumetric imaging of the cornea, capable of compensating both axial and lateral motion with micron-scale accuracy and millisecond-scale time consumption based on higher-order regression. System performance was evaluated during volumetric imaging of corneal phantom and bovine (ex vivo) samples that were positioned in the palm of a hand to simulate involuntary 3D motion. An overall motion-artifact error of less than 4.61 μm and processing time of about 3.40 ms for each B-scan was achieved.

Line-field confocal optical coherence tomography (LC-OCT) is an imaging technique based on a combination of confocal microscopy and OCT, allowing three-dimensional cellular-resolution imaging of the skin in vivo. We present the latest advances in LC-OCT to facilitate the use of the technique by dermatologists and improve the diagnosis and analysis of skin lesions. A video camera was incorporated into a handheld probe to acquire dermoscopic images in parallel with LCOCT images. A confocal Raman spectrometer was associated with a LC-OCT device to record morphological images of the skin in which points of interest can be subjected to molecular characterization.

We demonstrate ultra-large field of view OCT scanning using standard optics, a X-Y-galvanometer scanner and a synchronously driven motorized XYZ-positioning stage. The integration of a movable stage into our self-built 3.3 MHz- OCT system allows acquiring coherent ultra-large area images, fully leveraging the high speed potential of our system. For fast OCT-angiography, one galvanometer axis scanner is driven in a repetitive sawtooth pattern, fully synchronized to the movement of the linear stage, to obtain multiple measurements at each position. This technique requires exact synchronization, precise repositioning, and uniform movements with low tolerances to ensure a minimum revisitation error. We analyze error and performance of our setup and demonstrate angiographic imaging.

Radiation therapy remains an essential component of cancer treatment, with nearly 50% of cancer patients receiving radiation therapy at some point during the course of their illness. Of those, as many as 90-95% may experience some form of acute radiation dermatitis (ARD) or radiation-induced skin injury. ARD results in significant discomfort, restriction of daily activities, overall decrease in the quality of life and even cessation of the necessary radiation therapy with detrimental survival effects. Unfortunately, research into the causes and possible management strategies for ARD is hindered by the lack of biomarkers for the quantitative assessment of the early changes associated with the condition. This study provides the basis to yield such novel biomarkers using Optical Coherence Tomography (OCT) images with the extraction of conventional image intensity and novel features. Patients were imaged twice each week over the six-week course of their radiation treatment. The severity of the cases was graded by an expert oncologist. Preliminary results, separating normal skin from early ARD, were very promising, yielding an accuracy of 88.3%.

OCT has been exploited extensively in studies of cochlear mechanics due to its ability to non-invasively measure vibrations of various cochlear structures. A key limitation has been the ability to measure only in one dimension, along the optical axis. However, recent evidence suggests the organ of Corti has complex, three-dimensional vibratory micromechanics. Therefore, a 3D-OCT vibrometry system has been developed to measure the vector of motion within the cochlea and hopefully shed light on the underlying mechanics that lead to cochlear amplification and the exquisite sensitivity and frequency selectivity of mammalian hearing. The system uses three independent sample arms (channels) with a single reference arm to acquire vibrations, exploiting the long coherence length of the laser to depth encode the three channels. The system was first validated using a piezoelectric actuator. This yielded an RMS error of ≤0.3° in both polar angles with expected sensitivity to vibrational amplitude. Preliminary measurements in the cochlea of a live mouse demonstrate direction-dependent differences in vibratory responses.

We present a 3-D non-invasive OCT-based tissue dynamics imaging method to evaluate the tumor spheroid drug response. Our method depends on newly developed 3-D scanning protocol, which acquires the volumetric tomography in 52.4 s. The scanning protocol repeats raster scanning 32 times at each location in the tissue in 6.55 s. The tissue sub-cellular motion/viability is quantified by analyzing the OCT time sequence using our developed algorithms including “logarithmic intensity variance algorithm (LIV)” and “late OCT correlation decay speed (OCDS_l)”. The capability of our method has been investigated by evaluating the response of the human originated breast cancer (MCF-7) and colon cancer (HT-29) spheroids to anti-cancer drugs. The tissue viability alterations induced by the drug applications have been successfully visualized and quantified.

We present an ultra-fast single-shot line-field optical coherence elastography (LFOCE) technique based on a parallel line-field spectral domain optical coherence tomography system. The system was based on a Michelson-type interferometer, a supercontinuum broadband light source, and an ultra-fast 2D spectrometer. The peak sensitivity was ~102 dB, and the sensitivity roll-off was ~37 dB over 0.8 mm. The 1/e length along the line beam as measured by the signal to noise ratio (SNR) from an image of a mirror was 3.1 mm. The 1/e width across the line beam was measured by the knife-edge technique and was ~9.7 μm. The displacement stability as measured by standard deviation over 20 ms of a glass coverslip in common-path mode was 0.52 nm at an OCT SNR of 41 dB. The camera operated at a framerate of 25 kHz with 460 lateral pixels, resulting in an A-scan rate of 11.5 MHz. Validation was performed in gelatin phantoms of various concentrations, and the results corroborated well with mechanical testing. After validation in the phantoms, OCE measurements were performed in rabbit corneas in situ in the whole eye-globe configuration. The eyes were cannulated for artificial intraocular pressure (IOP) control. The elastic wave speeds in the cornea at 10, 15, and 20 mmHg were 3.03±0.05, 4.66±0.03, and 8.85±0.08 m/s, respectively. OCE measurements were also performed in an in vivo anesthetized rabbit, and the wave propagation was successfully captured. These results show the ability of the ultra-fast OCE system to measure changes in stiffness as well performing live measurements.

Transient-mode photothermal optical coherence tomography (TM-PT-OCT) is introduced as a high-speed and video rate implementation of PT-OCT. Here, the transient thermal response of samples to a low power PT laser pulsed excitation is interrogated through temperature-induced variations in the OCT phase signals. Results suggest that the proposed method enhances the PT-OCT imaging speed by more than two orders of magnitude compared to conventional PT-OCT with lockin detection. This enhancement not only enables video rate visualization of molecules of interest (MOI), but also opens the door for use of multiple PT lasers to perform spectroscopic PT-OCT for detection and differentiation of multiple MOI’s with distinct absorption spectra. To demonstrate feasibility, experimental results on detection and differentiation of lipid and collagen are presented and discussed.

The zebrafish is an essential animal model in pre-clinical research, especially in the field of cancer investigations. A polarization sensitive Jones matrix OCT (JM-OCT) prototype operating at 1310 nm was utilized to investigate adult control and tumor zebrafish models. Various anatomical features were characterized based on their inherent scattering and polarization properties. A motorized translation stage in combination with the prototype enabled large field-of-view imaging to investigate whole adult zebrafish non-destructively. The reflectivity, the attenuation coefficient and local polarization parameters such as the birefringence and the degree of polarization uniformity were analyzed to quantify differences in tumor versus control regions.

Accurate and robust estimation the scatterer size from Optical Coherence Tomography (OCT) images has the potential to provide a diagnostically useful biomarker of disease. In the past, Mie Theory with curve fitting, the autocorrelation of the spectrum and the bandwidth of the correlation of the derivative (COD) have been explored for this purpose. However, these approaches are very challenging to apply to scatterer sizes below 4 μm due to their inherent lack of accuracy or, in the case of COD, the limitations imposed by Mie Theory itself. On the other hand, the Fractal Dimension (FD) has been used in the analysis of OCT images to examine the structural variations of biological tissues. In this study, we propose the use of fractal analysis to robustly and accurately estimate the size of scatterers as small as 0.1 μm in diameter. The box counting method was used to define the statistical characteristics of the FD, first calculated for individual neighborhoods and, subsequently, for the entire image. Using a prudently selected subset of these features, the scatterer size of microsphere phantoms was estimated with a mean error of 32.8 %. The proposed method will, of course, have to be tested further both on an expanded phantom set but also on human normal and disease tissue. However, given the preliminary results presented in this study, this approach has the potential to be further developed and to perform in vivo scatterer size estimation.

Post-signal-processing techniques of refocusing and digital aberration correction of optical coherence tomography (OCT) restore the spatial resolution deteriorated by optical aberrations. In the case of in vivo biological tissues with Fourierdomain OCT, an ultrafast volumetric acquisition is required to avoid motion distortion. In point-scanning OCT, a fast scan is required, and the bulk phase shifts among surrounding A-lines should be corrected. A low duty cycle might be necessary to obtain the consistent en face image with a high-speed raster scan. Recently, we have demonstrated a Lissajous-patternbased probe beam scanning and motion correction algorithm. In this study, we demonstrate a Lissajous-cycle-wise (LCW) digital refocus algorithm. The algorithm of LCW digital refocus is based on a convolution operation with an inverse filter. The complex OCT signals sampled with a Lissajous cycle are going to be convolved with an inverse filter of defocus. The reconstruction from Lissajous data to the Cartesian coordinate assigns a Cartesian grid to each A-line. By merging A-lines of different cycles, blurring due to defocus perpendicular to the scanning trajectory is mitigated by other cycle data. The phantom experiment is applied for the proof of concept. A prototype 1-μm spectral-domain OCT system is used for experiments. The A-line rate is 92 kHz. The blurred image of a phantom by defocusing is sharpened by the LCW digital refocus process along with all directions in the en face plane. Although the restored resolution does not reach the diffraction limit, an ultrafast volumetric acquisition is not required when one Lissajous cycle is significantly faster than sample motion.

Line-field confocal optical coherence tomography (LC-OCT) is a high-resolution imaging technique based on a combination of time-domain optical coherence tomography and confocal optical microscopy, with line illumination using a spatially coherent broadband light source and line detection using a line camera. We present a LC-OCT device based on a Mirau interferometer consisting of an immersion microscope objective incorporating a miniature interferometer. The device can acquire 17 B-scans per second, which is the fastest acquisition rate reported to date in LC-OCT. By stacking multiple adjacent B-scans, a 3D image with a lateral field of view of 940 μm × 600 μm over a depth of 350 μm can be acquired. Compared to the conventional LC-OCT devices based on a Linnik interferometer, this Mirau-based device has advantages in terms of compactness, weight, and B-scan acquisition speed. Imaging of skin tissue with near-isotropic resolution of ~1.5 micron is demonstrated in vivo.

Skin cancer is one of the most prevalent types of cancer in the world, with a steadily increasing incidence rate and associated health burden [1, 2]. While it is generally treatable when detected, survival rates decrease dramatically as the disease progresses – highlighting the importance of early detection [3]. Unfortunately, the current gold standard in diagnosing skin cancers involves taking biopsies followed by histopathology, which is invasive and time consuming. Some studies have shown that the majority of biopsies ordered by primary care providers were found to be benign, meaning that biopsies are often performed when there is no cancer present [4]. Given this, there is a great interest in developing noninvasive diagnostic tools for skin imaging. Optical coherence tomography (OCT) is an imaging modality that is particularly well suited for this area, owing to its ability to provide high-resolution (3-15 μm) volumetric data at a penetration depth of up to 1.5 mm [5]. In a manner analogous to ultrasound, it provides cross-sectional images which can be comparable to histology slides [6]. However, conventional intensity-based OCT only provides structural information with no functional contrast, and as a result it has encountered difficulty in diagnosing specific cancers such as melanoma [7]. Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT which can characterize polarization properties such as the birefringence of tissue samples – birefringence specifically occurs in fibrous structures such as collagen [8]. Several groups have investigated birefringence in skin tissue using PS-OCT, but little work has been done with the more recently defined degree of polarization uniformity (DOPU) contrast. The functional contrast provided by DOPU PS-OCT imaging can provide localized, depth-resolved information on the polarization scrambling properties of samples. A specific example of this is in ophthalmic imaging, where DOPU contrast in PS-OCT imaging demonstrated the ability to segment the retinal pigment epithelium – a layer otherwise hard to differentiate in intensity-based OCT imaging [9]. To our knowledge, very few if any groups have investigated PS-OCT imaging with DOPU contrast in understanding the layered-structure of skin. We have recently investigated the DOPU in skin tissue phantoms and reported that DOPU is sensitive to surface roughness – an important factor in differentiating skin cancers from benign lesions. Our group has a previously reported PS-OCT system that can simultaneously acquire reflectance, phase retardation (birefringence), and DOPU images that we aim to use in this study to expand on our previous work and further investigate polarization properties in skin in vivo [10].

In the biological and pharmaceutical research, there is a certain demand for label-free three-dimensional (3D) imaging of tissue function. Dynamic optical coherence tomography (OCT) has been demonstrated to fill this demand, but a very high-speed system is required for a volume acquisition of dynamic OCT. Here we demonstrate two new frame acquisition protocols which potentially enable the volumetric dynamic OCT by standard-speed OCT device with a reasonably short measurement time. One of the protocols takes multiple frames at a single location with a few hundred milliseconds interval. The other sequentially takes four frames at a single location, and then repeats this burst four-frame acquisition eight times with a few hundred milliseconds interval. These protocols were validated with in vitro and ex vivo samples. Both protocols gave reasonable dynamic OCT images.

3D cell models indicate stronger similarities in vivo than monolayer cell culture, and thus is raising awareness as an important tool for evaluating biological phenomena, drug action, and mechanism of diseases. This paper compared two imaging systems for accurate measurements of the morphological structure and volume quantification of 3D tumor spheroids. The two imaging systems are OCT using a scan lens and EDOF-OCM, which uses a Bessel beam to expand the depth of field. Human hepatoma cells were used for spheroid formation. To compare the effectiveness of the imaging system, we measured the spheroid structure according to cell number per spheroid and growth per day. Although both systems were able to acquire the morphological structure and quantify volume of 3D tumor spheroids the OCM using the Bessel beam was able to more accurately measure the overall structure of the spheroid without surface reflection.

Time-stretch dispersive Fourier transform is an all-optical processing method for real-time Fourier transformation of ultrafast optical signals that allows for the implementation of Optical Coherence Tomography (OCT) at tens of MHz Ascan rates. In this work we propose and demonstrate a Time-Stretch OCT (TS-OCT) method that supports multiple probes with minimal increase in complexity and cost of the system. The new method can be employed to expand the scannable area of TS-OCT system without sacrificing the x-y spatial resolution. The proposed method is based on using a Wavelength Division Multiplexer (WDM) device in the signal arm of the TS-OCT system connected to multiple independent imaging probes. The signal path in majority of the system is common for all the probe signals including the interferometer, highly dispersive element, optical amplifier, photo receiver, and digitizer channel. Different probe spectra interference signals are separated digitally in digital post processing on the computer. This method allows to have the benefit of multi-probe systems in TS-OCT systems with minimal increase in the system complexity and cost.

In this work we configure Haralick's texture parameter contrast to match the dimensions of characteristic structural features in ex vivo samples from glioblastoma (GBM) resection imaged with optical coherence tomography (OCT). The aim is to find and tune different texture features in a way that they enable the best possible basis for tissue classification using support vector machines (SVM). We used a sample collective including 18 tissue samples comprising 9 samples with at least 90% vital tumor and no healthy tissue, as well as 9 samples with 100% healthy tissue. All samples were imaged ex vivo immediately after resection. As a reference all samples were then examined professionally in the department of histopathology to determine tissue percentages. Based on the acquired 3D OCT images, texture features were extracted and optimized supported by the knowledge of medical professionals. Relations between the size of characteristic structures in healthy tissue as well as in GBM and different texture features were examined and evaluated. We focused on texture parameters as proposed by Haralick, relying on gray-level co-occurrence matrices (GLCMs). The displacement vector for the determination of those GLCMs was matched with size and direction of the characteristic structural tissue features of healthy and tumorous tissue. The results serve as a starting point to optimize the classification process of GBM against healthy tissue using SVM.

We propose a new multi-focus average method for optical coherence tomography, to reduce the multiple scattering signals and improve the visibility of the sample structure in the deep region. It combines computational refocusing, complex averaging, and multiple acquisitions with focal shifting. A scattering phantom was measured to validate the suppression of multiple scattering signals and the contrast improvement at the deep region.

Deep learning-based models have been extensively used in computer vision and image analysis to automatically segment the region of interest (ROI) in an image. Optical coherence tomography (OCT) is used to obtain the images of the kidney’s proximal convoluted tubules (PCTs), which can be used to quantify the morphometric parameters such as tubular density and diameter. However, the large image dataset and patient movement during the scan made the pattern recognition and deep learning task to be difficult. Another challenge is a large number of non-ROIs compared to ROI pixels which caused data imbalanced and low network performance. This paper aims at developing a soft Attention-based UNET model for automatic segmentation of tubule lumen kidney images. Attention-UNET can extract features based on the ground truth structure and hence the irrelevant feature maps are not contributed during training. The performance of the soft-Attention-UNET is compared with standard UNET, Residual UNET (Res-UNET), and fully convolutional neural network (FCN). The original dataset contains 14403 OCT images from 169 transplant kidneys for training and testing. The results have shown that soft-Attention-UNET can achieve the dice score of 0.78±0.08 and intersection over union (IOU) of 0.83 which was as accurate as the manual segmentation results (dice score = 0.835±0.05) and the best segmentation scores among Res-UNET, regular UNET, and FCN networks. The results show that CLAHE contrast enhancement can improve the segmentation metrics of all models significantly (p < 0.05). Experimental results of this paper have proven that the soft Attention-based UNET is highly powerful for tubule lumen identification and localization and can improve clinical decision-making on a new transplant kidney as fast and accurately as possible.

Owing to the fast-acquisition times and long-imaging ranges provided by swept-source optical coherence tomography (SSOCT), it has seen widespread commercial success in a wide range of real world applications. However, the high-cost and bulky size of swept-source lasers limits the potential application range of the technology. Here, a SS-OCT system utilizing a low-cost and compact wavelength-tunable laser designed for telecommunications is presented. The limited tuning range and discontinuous tuning of the telecommunications laser, is overcome through the use of compressed sensing, enabling the acquisition of OCT scans with enhanced resolutions and signal-to-noise ratios.

We describe the optimization and application of a multi-window approach for improved resolution, side-lobe suppression, and phase sensitivity. Using the Hann window as a reference, we show that 10 windows are sufficient to achieve 42% resolution improvement, -31 dB side-lobe intensity, and a 20% improvement in phase sensitivity. We explored the benefits of this windowing technique for OCT imaging using a prototype narrow-band laser, OCT vibrometry, and Doppler OCT for angiography. Experimental data are in good agreement with simulation. We believe it will be possible using this optimized approach to achieve real-time processing and display, despite the added computational load.

In Intensity Correlation Optical Coherence Tomography (ICA-OCT), an OCT spectrum is processed into a two-dimensional signal incorporating elements which do not correspond to the structure of the imaged object. These elements, called artefacts, display a very well-defined behaviour in the presence of uncompensated chromatic dispersion. More importantly, their behaviour reflects only the dispersion of the layer which the artefacts uniquely correspond to. We show preliminary results indicating that a neural network can interpret this layer-specific behaviour and output corresponding Group Velocity Dispersion values, thus creating a depth-resolved dispersion profile of the object.

Infrared (IR) lasers have recently been tested as an alternative to electrosurgical and ultrasonic laparoscopic devices for optical sealing of blood vessels. IR laser technology previously demonstrated faster sealing times, reduced thermal spread, and lower device temperatures during experimental studies. However, current commercial laparoscopic devices incorporate electrical impedance and/or temperature sensors as real-time, closed-loop, feedback to indicate successful blood vessel seals. This preliminary study explores an infrared laser system for sealing and optical coherence tomography (OCT) as a potential feedback system for successful vessel seal verification. A 1470-nm diode laser delivered an incident power of 30 W for an irradiation time of 5 s using an 8 x 2 mm linear beam, for creating strong seals in porcine renal blood vessels under compression. After sealing the blood vessels, OCT was performed on unsealed and sealed vessel regions for comparison. Standard vessel burst pressure (BP) measurements confirmed successful seals after OCT. Integrated reflectance intensity in OCT A-scans decreased by an average of 20 ± 6% in sealed versus native vessels of 2.4 ± 0.4 mm diameter. Vessel BP measured 532 ± 239 mmHg, with all vessels (n = 25) recording a successful BP < 180 mmHg (hypertensive blood pressure). Unsealed vessels demonstrated significantly deeper imaging marked by a continuous decay in reflected intensity, while sealed vessels showed subsurface reflectance intensity peaks, immediately followed by a rapid decay in reflectance intensity. These markers are consistent with increased light scattering and decreased optical penetration depth upon thermal coagulation of tissues. A-line OCT data consistently differentiated between sealed and unsealed blood vessel regions. Future work will involve OCT integration into the laparoscopic device for real-time optical feedback during IR laser sealing.

Skin and subcutaneous tumors are widespread in dogs and cats. Current tumor diagnostics (e.g., biopsy, fineneedle cytology) is invasive and labor-consuming. In this work, we studied ex vivo the most common canine and feline tumor OCT images using sliding window analysis and linear SVC classification, and we compared different sliding window sizes to determine the most optimal window sizes when differentiating between skin, mast cell tumours and soft tissue sarcomas. Sensitivities and specificities of all tissue classes saw an increase with increasing window size at small window size values and plateaued at around 60-80 μm, indicating the most significant tissue structures for differentiation via SWA likely lay here. Our work is the first veterinary OCT study on multiple canine and feline skin tumors to optimize the sliding window size for image pattern analysis.