This PDF file contains the front matter associated with SPIE Proceedings Volume 11078, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

We implemented a real-time video-rate 4D-OCT system with virtual reality display. To achieve the required low latencies we optimized the dataflow path and the placement of the necessary synchronization points. Employing temporal reprojection enables to perform volume rendering at 1/3 of the display refresh rate, yet maintaining smooth updates to the HMD; thus we achieve display updates at 90Hz, volume rendering at 30Hz and C-scan acquisition at <15Hz. By mounting of a tracking accessory to the scanning head we can render the OCT volume in virtual space in the position of the actual imaging volume.

In Fourier-domain optical coherence tomography, finite acquisition bandwidths can limit the achievable imaging range, axial resolution, and/or imaging speed. Circular ranging (CR) methods were recently demonstrated to overcome these barriers [1,2,3]. By using optical frequency combs (FC), the depth space of the interferometric signal is folded such that extended imaging ranges are compressed into a reduced RF bandwidth. To avoid overlap of artefacts, this folding is performed in a circular manner through the combination of a frequency comb optical source and the use of complex demodulation, i.e., the detection of in-phase (I) and quadrature fringe signals (Q) that resolve the sign of the measured delay. Complex demodulation methods have been explored in Fourier-domain OCT to extend the imaging range by a factor of two through use of the positive and negative delay spaces. Passive methods based on optical quadrature circuits and active methods based on dynamic phase modulation have been demonstrated. In prior CR OCT demonstrations, a passive method was employed [1]. While this provided the required performance, there may be advantages in active methods that reduce digitizer channel counts and avoid the need for environment stability. In this work, we describe the extension of active demodulation schemes to CR OCT systems. In this, we highlight CR-specific alterations that overcome these limitations. We demonstrate the active demodulation methods using a stretched pulse active mode locked (SPML) FC laser at 1.3 μm for the first time.

"Full-wave" models of OCT imaging systems based on Maxwell's Equations are beginning to emerge as feasible alternatives to well established approximate models. These models are however computationally taxing when dealing with large samples. Here, in an effort to reduce the computational burden, we present a means of synthesizing full-wave scanning-mode OCT image formation using only a single simulation of a plane wave incident on a given sample medium. The method involves an angular spectrum approach which synthesizes the signal for arbitrary scan positions, and arbitrary illumination conditions. This is demonstrated to reduce the required simulation time by an order of magnitude when synthesizing OCT B-scans, as compared to previous methods which require a separate simulation for each scan position.

Full-field swept-source optical coherence tomography (FF-SS-OCT) achieves high resolution imaging with wide-field illumination and parallel Fourier-domain detection. However, FF-SS-OCT is strongly susceptible to the cross-talk-generated noise from spatially coherent lasers. Here, we demonstrate how to overcome this problem with spatiotemporal optical coherence (STOC) manipulation. In STOC the time-varying inhomogeneous phase masks modulate the incident light. We show that by properly adjusting these phase masks, the spatial coherence can be reduced. As a result, the imaging system becomes spatially incoherent. Thus, the cross-talk-generated noise as well as the low-order geometrical aberrations can be suppressed. STOC approach is validated by imaging 1951 USAF resolution test chart covered by diffuser, scattering phantom and the rat skin ex vivo.

We derive a physically accurate and computationally efficient Monte Carlo algorithm that can be used to evaluate the complex statistics of speckle fields in scattering media. This allows evaluating and studying second-order speckle statistics, such as the memory effect, for a large variety of material and imaging parameters, including turbid materials. This helps bridge the gap between analytical formulas, derived under restrictive assumptions such as diffusion, and empirical lab measurements. It also opens up the possibility for discovering new types of correlation effects, and using those to improve our ability to see through and focus into random media.

MHz-OCT systems based on FDML swept laser sources combined with the massive parallel processing capabilities of modern computer hardware enable volumetric imaging, processing and stereoscopic display at video rates. The increasing image quality and speed might enable new fields of application where the volumetric OCT completely replaces stereoscopic microscopes instead of being a mere supplement. Aside from the depth resolving capability, a particular advantage is the ability to display a whole image volume from arbitrary points of view without the need to move the actual microscope or to rotate the patient’s eye. Purely digital microscopy is already offered as alternative to traditional through-an-eyepiece surgical microscope. We explore the use of virtual reality to present digital OCT microscopy images to a trained surgeon, carrying out a series of surgical procedures ex-vivo on a porcine eye model.

A principal tool for the visual inspection of the middle ear in the hearing clinic is the surgical stereo-microscope. We have developed a compact accessory for the surgical microscope that enables volumetric optical coherence tomography (OCT) imaging of the middle ear as well as functional vibratory imaging with subnanometer sensitivity. The sensitivity to vibration is achieved by careful engineering of the microscope attachment and frequency-domain processing. The microscope attachment integrates the entire OCT interferometer onto a custom aluminum base that mounts directly to the accessory area at the foot of most surgical microscopes. This approach is effective at removing high-frequency phase-noise, thus enabling near shot-noise limited sensitivity above ~2 kHz even though the OCT system is suspended above the patient by a boom arm. We analyze the vibratory response in the frequency domain, hence our ability to measure vibrations in the tympanic membrane and ossicles is near the shot-noise limit. As a demonstration of this system we have recorded in vivo volumetric images of a healthy human patient as well as the vibratory response at the tympanic membrane down to the hearing threshold. We also show that it is possible to use time averaging to drive the noise floor down below 2 pm which allowed us to make the first measure of distortion product otoacoustic emissions (DPOAE) using OCT. Finally, the system can easily be taken on and off of the surgical microscope and when in use does not impinge on the normal view through the surgical microscope.

Vascular anastomosis, connecting two vessel ends together, is the foundation of plastic and reconstructive surgery. Every living tissue transplantation requires vascular anastomosis. While optical coherence tomography (OCT) imaging can provide objective information for intraoperative evaluation, currently it suffers from limited imaging penetration depth for relative large vessels, which will result in information loss at the bottom region of vessel. In this work, we designed a multi-view scanning scheme for the vessel imaging to increase the FOV effectively. To push the clinical translation, we used MEMS mirror to steer the beam and made a miniature handheld probe for testing. Preliminary results on IR sensing card, multilayer scotch tape, and plastic tube imaging showed the performance of our probe.

Over the last two decades optical coherence tomography (OCT) has become a clinical gold standard in diagnostic and management of many retinal diseases. Following that success, OCT is now becoming a standard tool in studies of animal models of human retinal diseases allowing longitudinal evaluation of disease progression and responses to therapeutic intervention in the single animal. Recent progress in OCT data acquisition and processing allowed successful cellular resolution detection of outer and inner retina functional response to light stimulation both in humans and experimental animals. In this manuscript, we will describe our latest effort of improving cellular contrast in mouse functional retinal imaging by application of volumetric registration and speckle contrast reduction by temporal averaging of volumetric data sets: i.e., temporal Super Averaging. As an example, the current configuration of our multimodal Scanning Light Ophthalmoscopy / Optical Coherence Tomography (SLO/OCT) mice retinal imaging system, as well as data acquisition and processing schemes, will be presented. Experimental results will be discussed in the context of improved morphological and functional probing of mice retinas at cellular resolution. Finally, current limitations and future directions of instrument development with a focus on improved probing of the retinal function will be discussed as well.

A post-processing pipeline was created for white light optical coherence tomography, resulting in depth-resolved hyperspectral imaging. This method was tested on both melanin phantoms and in the RPE of rodent eyes, showing that due to its granular nature, melanin can be detected in this manner.

Sensorless Adaptive Optics (SAO) allows easy integration of adaptive optics in retina imaging systems, however the iterative nature of the SAO optimization process requires long time to perform aberration correction and the inevitable subject motion during the optimization could compromise the AO correction. Here we present a multi-modal SAO retina imaging system that includes Optical Coherence Tomography (OCT), OCT-Angiography, confocal Scanning Laser Ophthalmoscopy (cSLO), and fluorescence detection. To mitigate the motion artifact and increase the SAO performance, we developed volumetric image tracking to extract merit function of SAO only within the region of interests.

Malignant melanoma is by far the most dangerous type of skin cancer. Currently, the gold standard to diagnose melanoma in the clinic is excisional biopsy and histopathologic analysis. Approximately 15-30 benign lesions are biopsied to diagnose each melanoma. Additionally, biopsies are invasive and result in pain, anxiety, scarring and disfigurement of patients, and they can be a financial burden to the health care system. Among several imaging techniques developed to enhance melanoma diagnosis, optical coherence tomography (OCT) with its high-resolution and intermediate penetration depth can potentially provide required diagnostic information, noninvasively. We propose an image analysis algorithm, ‘optical properties extraction (OPE)’ that drastically improves the specificity and sensitivity of OCT by identifying unique optical radiomic signatures pertinent to melanoma detection. We evaluate the performance of the algorithm using several tissue-mimicking phantoms. We then test the OPE algorithm with sixty-nine human subjects and demonstrate that melanoma can be differentiated from benign nevi with 97% sensitivity, and 98% specificity.

While dental caries represents the major chronic disease of humans, visual and tactile inspection are the methods of choice in daily dental practice. Several optical technologies have been developed in recent years for the purpose of dental examination, including near-infrared light transillumination as a promising tool for the supplementation and partial replacement of radiography. In case of occlusal alterations, the incidence of surface discolorations impedes the visual assessment, whereas tactile inspection appears to yield little diagnostic information or might be detrimental. Optical coherence tomography (OCT) facilitates depth-resolved imaging with μm resolution, utilizing near-infrared light, and has already shown its potential for various dental applications. We have recently demonstrated that depolarization imaging utilizing the degree of polarization uniformity (DOPU) extends those abilities by the detection of early carious lesions, as it provides an unambiguous demineralization contrast. Here, we show that this approach also enables the assessment of occlusal enamel lesions in the presence of stains, and compare PS-OCT cross sections with polarized light microscopy (PLM) images of thin sections. For tooth samples with discoloration or demineralization, respectively, PS-OCT and PLM results are in good agreement.

Our study targets improved and accelerated diagnostics of bladder cancer with optical coherence tomography (OCT) and Raman spectroscopy (RS) ex vivo. OCT provides structural information on the penetration depth of the lesion, whereas RS complements this information with molecular characteristics regarding the likelihood of growth and spreading. Hence, the diagnostic findings include the determination of stage and grade of a tumor. The bladder specimens were scanned with OCT to detect suspicious lesions. Thereby, OCT was used as a red-flag technology to examine the bladder wall for abnormal tissue. Malignant bladder wall could be discriminated from healthy tissue. Upon identification of a cancerous lesion, RS added diagnostic information with molecular characteristics of the tumor regarding the grade. Texture analysis of OCT tomograms followed by k-nearest neighbour classification determined the stage of the lesion. Principal component analysis (PCA) of Raman spectra allowed for dimension reduction which was also fed into a knearest neighbour classifier allowing for classification of low-grade and high-grade tumors. We obtained an accuracy of 71% and 93% for staging and grading, respectively.

The preliminary results of the project devoted to the use of optical coherence tomography technique to evaluate the middle ear effusion condition are presented. The method of estimation of the middle ear effusion viscosity using the Fourier analysis of the OCT data is proposed. The method provides the possibility to distinguish areas filled by water and effusion in situ. The data on use of the especially-developed SD OCT system is reported.

Optical coherence tomography (OCT) applications like ultra-widefield and full eye-length imaging are of high interest for various diagnostic purposes. In swept-source OCT these techniques require a swept light source, which is coherent over the whole imaging depth. We present a zero roll-off 1060 nm Fourier Domain Mode Locked-Laser (FDML-Laser) for retinal OCT imaging at 1.7 MHz A-scan rate and first long-range imaging results with it. Several steps such as improved dispersion compensation and frequency regulation were performed and will be discussed. Besides virtually no loss in OCT signal over the maximum depth range of 4.6 mm and very good dynamic range was observed. Roll-off measurements show no decrease of the point-spread function (PSF), while maintaining a high dynamic range.

The optical coherence tomography (OCT), typically used in the visible wavelength range, due to relatively long wavelength is limited by the axial resolution to approximately a few hundreds of nanometers to a micron. Visible light is also incapable of resolving multilayered structures of tens of nanometers periods. Thus, the extension of the OCT to shorter wavelengths, such as the extreme ultraviolet (EUV) and soft X-ray (SXR), in the so-called X-ray coherence tomography (XCT), allows mitigating those problems. We present a nanometer resolution XCT using broadband SXR radiation with 2 nm axial resolution using a compact laser plasma soft X-ray source. The laser-produced Kr/He plasma was formed by the interaction of nanosecond laser pulses with a gaseous target in a double stream gas puff target approach, emitting 2 to 5 nm wavelength broadband radiation. The coherence parameters of the SXR radiation allowed for the OCT measurements of a bulk multilayer structure composed of Mo/Si multilayers with 10 nm period, with an axial resolution of about 2 nm, the interface position accuracy of sub-nm and detection of multilayer interfaces up to a depth of about 100 nm. The experimental data were compared to the OCT simulations.

A swept source optical coherence tomography (SS-OCT) system with the interferometer engine being a photonic integrated circuit (PIC) has been developed. Furthermore, an Arrayed Waveguide Grating (AWG), representing a grating on a PIC, for spectral domain OCT (SD-OCT) has been integrated in a fiber-based OCT system. With measured sensitivities of ~87 dB (SS-OCT) and ~80 dB (SD-OCT), scattering tissue imaging becomes feasible for OCT-on-chip systems. In this study, we present two OCT-on-chip systems and first results of biological tissue imaging in-vivo and exvivo.

We demonstrate an 840-nm broadband and compact light source with 140 nm FWHM optical bandwidth and 8 mW of output power, realized with three superluminescent diodes (SLEDs) that are, to our knowledge for the first time, integrated on a free-space, micro-optical bench in a standard 14-pin butterfly package. The three SLED chips at 790 nm, 840 nm and 880 nm are mounted on a ceramic baseplate that is temperature-stabilized by a thermo-electric cooler. The light output of the SLEDs is collimated by micro-optical collimation lenses, spectrally combined through free-space dielectric edge filters and focused into a HI-780 single-mode fiber. The combined broadband spectrum corresponds to a coherence length of 2.9 μm in air, suitable for ultra-high-resolution OCT systems.

An automated heterodyne method is proposed to characterize sampled grating distributed Bragg reflector (SG-DBR) lasers in terms of their lasing output wavelength, side-mode suppression ratio (SMSR) and output power. Such lasers are the core of akinetic all-semiconductor based swept sources for Optical Coherence Tomography (OCT) systems. The purpose of the paper is to demonstrate the technique and obtain a broader optical and electrical understanding in DC and AC operation. A JDSU Agile SG-DBR laser was characterized and found to have a tuning range ≈ 60 nm, a center wavelength λ_c = 1540 nm and average lasing power of 10 mW. The result of the AC characterization is a ‘tuning dictionary' that contains 379 tuning points (10 μs per tuning point).

We demonstrate a preliminary setup of a combined MHz-OCT and RGB narrowband reflection microscope and investigate the performance of the new RGB branch and different display modes of colored OCT data sets.

Development of noninvasive diagnostic techniques in clinical practice, especially sufficiently fast methods suitable for intraoperative use, remains a topical and challenging problem in modern medicine. Compressional Optical Coherence Elastography (OCE) that has a high potential to be intraoperatively applied. This study reports preliminary results on application of compressional OCE for identification of tumor margins and even differentiation of breast cancer types with low- and high- histological grades, i.e., a step towards creation of a kind of OCE-based optical biopsy. The reported variant of OCE utilized B-scans with scales ~2-4 mm comparable with typical scales of histological samples. The approach is based on the ability of OCE to quantitatively visualize distribution of the Young modulus (stiffness) in studied tissue samples, which then is used to perform "elasto-spectroscopy" generically resembling the massspectroscopy procedures. The procedures of the OCE examination do not require any special preparation of tissue samples and thus can be applied intraoperatively on time intervals ~ a few minutes with immediately available results. In the reported study, the samples after OCE examinations were subjected to histological studies and classification made by an experienced histopathologist. Comparison between the OCE results and histological data made it possible not only to distinguish between normal tissue and tumor (for determining resection boundary), but also to formulate OCE-based criteria allowing for differentiation between carcinomas of low grades and fairly good treatment prognosis and highgrade invasive tumors with poor prognosis. Similarly, identification of not only invasive breast tumors, but also benign breast lesions, intermediate between norm and malignant tumors can be made.

Previously, we have demonstrated two fiber optic catheter implementations of dual-beam manually-actuated distortion-corrected imaging (DMDI) that employ rotationally-scanning micromotors that are potentially suitable for endoscopic imaging applications. These catheters are able to correct for both axial (push/pull) and azimuthal (catheter rotation) manual actuation. We presented a multiplexed dual beam micromotor catheter (mDBMC), an OCT-specific design that depth-multiplexes both imaging channels within a single optical fiber and a dual-fiber parallel DBMC (pDBMC) design that is suitable for any point-scanning modality such as OCT, fluorescence, or reflectance imaging. As the mDBMC has a relatively simple scan pattern, we developed a straightforward automated method for distortion correction based on image frame cross-correlation. Due to the complicated scan pattern of the pDBMC, we initially co-registered image features for the pDMBC in a time-consuming manual process. In this work, we describe our efforts to develop an automated distortion correction method for the pDMBC. We demonstrate initial success in automated correction along the pullback dimension.

Optical coherence tomography (OCT) with microscopic resolution is suited for the investigation of dynamic processes on cellular level. Most existing setups for microscopic OCT (mOCT) are able to acquire A-Scans at 100 kHz, hence they are suitable for displaying only B-Scans in real-time. We present an mOCT setup with a new high-speed spectrometer, which is capable of acquiring up to 600.000 A-scans/s. Customized software allows to image mOCT volumes with micrometer resolution at video rate. Therefore, we are able to visualize functional processes on a cellular level in three dimensions over time. Here, we present 2D and 4D data of ex vivo human lung. Recording tens of high-resolution OCT volumes per seconds becomes possible faster than previous setup for OCT with microscopic resolution.

Optical Coherence Tomography (OCT) is nowadays being widely employed as a diagnostic tool for skin cancer. It can produce feedback on tissue morphology alterations produced by different pathologies. OCT images are mainly produced by differences in refractive index and attenuation coefficient, providing in-depth information. Intensity OCT images display the effect of tissue alterations on backscattered light, but it does not represent real physical magnitude. In a number of occasions, morphology alteration events within the same tissue type, produce intensity variations in OCT images that can be misclassified as different tissue component. The estimation of depth-resolved attenuation coefficient improves tissue contrast, helping to identify tissue identity and isolating the effect of disordered structures of the same tissue. The proposed methodology shows that melanoma and Basal Cell Carcinoma (BCC) pathologies exhibit different optical parameters in depth. This enhances the identification of subsurface skin features.

Optical coherence tomography (OCT), a non-invasive label-free depth resolved imaging technique, facilitates cellular level structural and functional imaging of living animal and human tissues, but the structural sensitivity and resolution are fundamentally limited to microscale. Detection of structural changes in biological samples at nanoscale poses a significant challenge to both researchers and healthcare professionals. Furthermore, when considering physiological processes, it is desirable to be able to resolve these structural changes both spatially and temporally. Here, we present a novel method for detecting nanoscale structural changes non-invasively. This technique is based on adaptation of the correlation mapping approach to nano-sensitive optical coherence tomography (nsOCT). Our work describes the principles of this technique and demonstrates the feasibility of correlation mapping nano-sensitive optical coherence tomography (cm-nsOCT) by monitoring internal structural changes within different objects, including human skin in vivo. Structural changes can be visualized at each point in the sample over space or time. The experimental results show new possibilities for the study of structural changes, without the need for biomarkers or labels. Thus, cm-nsOCT could potentially offer exciting and far-reaching opportunities for early disease diagnosis, as well as myriad applications for researchers.

Noise in speckle-prone optical coherence tomography tends to obfuscate important details necessary for medical diagnosis. In this paper, a denoising approach that preserves disease characteristics on retinal optical coherence tomography images in ophthalmology is presented. We propose semantic denoising autoencoders, which combine a convolutional denoising autoencoder with a priorly trained ResNet image classifier as regularizer during training. This promotes the perceptibility of delicate details in the denoised images that are important for diagnosis and filters out only informationless background noise. With our approach, higher peak signal-to-noise ratios with PSNR = 31.0 dB and higher classification performance of F₁ = 0.92 can be achieved for denoised images compared to state-of-the-art denoising. It is shown that semantically regularized autoencoders are capable of denoising retinal OCT images without blurring details of diseases.

5-aminolevulinic acid positive brain tumor samples were investigated with a multimodal visible light optical coherence microscope (OCM) and fluorescence imaging (FI) setup. Tumor specific contrast was achieved by the FI part while the three-dimensional tissue morphology was assessed by the OCM part of the setup.

Optical coherence tomography (OCT) is a non-invasive imaging technique which is currently investigated for intraoperative detection of residual tumor during resection of human gliomas. Three different OCT systems were used for imaging of human glioblastoma in vivo (830nm spectral domain (SD) OCT integrated into a surgical microscope) and ex vivo (940nm SD-OCT and 1310nm swept-source MHz-OCT using a Fourier domain mode locked (FDML) laser). Before clinical data acquisition, the systems were characterized using a three-dimensional point-spread function phantom. To distinguish tumor from healthy brain tissue later on, attenuation coefficients of each pixel in OCT depth profiles are calculated. First examples from a clinical study show that the pixel-resolved calculation of the attenuation coefficient provides a good image contrast and confirm that white matter shows a higher signal and more homogeneous signal structure than tumorous tissue.

The choriocappilaris layer is considered to be one of the first retinal layers affected in age related macular degeneration and other retinal diseases [1]. Imaging this fine vascular layer below the retinal pigment epithelium (RPE) with optical coherence tomography angiography (OCTA) has been very challenging due to the high scattering and absorption of the RPE. In OCTA higher inter B-scan times increase the sensitivity for slow motion and hence improve the contrast of fine vessels. However, it was demonstrated that for the choriocappilaris the opposite is the case [2]. Novel swept source laser technology enables acquiring images at A-scan-rates of 1.7 million A-scans per second, which is approx. 17 times faster than the fastest commercially available OCT devices [3, 4]. OCTA images of the human macula with different inter B-scan times were acquired and compared. The same prototype system was also used to acquire single shot wide-field OCTA images with up to 60 degree field of view.

Adaptive optics optical coherence tomography (AO-OCT) provides depth resolved images of the retina with cellular resolution [1, 2]. So far, various cell types have been visualized with this technique including rod photoreceptors [3], retinal pigment epithelium cells [3, 4] or Ganglion cells [5, 6]. However, a translation of this technology into clinical settings remains challenging as AOOCT systems are quite bulky and complex to operate. In addition, the clinical benefit of AO-OCT imaging has not yet been demonstrated as especially elderly patients are difficult to image. This presentation gives an overview over the performance of AO-OCT technology in a clinical setting.

Optical coherence tomography angiography (OCT-A) is a non-invasive imaging modality allowing researchers and clinicians to view the retina in micrometer-scale detail. Acquired OCT-A volumes are three-dimensional, allowing the visualization of the superficial capillary plexus (SCP) and the deep capillary plexus (DCP). This provides valuable information towards the identification of pathologies such as diabetic retinopathy (DR). However, because an OCT-A volume is acquired over several seconds, motion artifacts caused by rapid movements of the subject’s eye (also known as micro-saccadic motion) can greatly reduce the quality, and subsequently the clinical utility, of the resulting volumes. Hardware motion tracking aims to reduce the effect of motion, but non-rigid registration is still often required for averaging sequentially acquired images. Furthermore, not all prototype OCT-A systems have tracking capabilities, particularly adaptive optics (AO) systems. Because of this, image registration is essential for the elimination of motion artifacts in OCT-A volumes, increasing their clinical diagnostic value. To further improve the clinical utility of these OCT-A images, segmentation is essential as it allows for the quantitative analysis of the microvasculature, which include the identification of the foveal avascular zone (FAZ) and areas of capillary non-perfusion (CNP), two biomarkers for the progression of DR.

Two-Photon Excited Fluorescence (TPEF) is a common modality for volumetric imaging within a biological sample. The molecule-specific contrast of TPEF imaging of the retina enables novel in vivo studies of disease and retina physiology. Furthermore, retinal studies can be aided by imaging the relevant cells, which can be fluorescently labelled with fluorophores such as GFP. The multiphoton absorption suppresses the out-of-focus background signal and improves with the axial sectioning without a confocal aperture in the optical detection path. Imaging the retina with near infrared (NIR) light is ideal since the retina contain visual pigments that are sensitive to visible wavelengths and NIR light has less scattering within biological tissue than shorter wavelengths. However, high pulse energy is required to generate the TPEF, yet minimizing the incident exposure energy is required for non-invasive imaging. TPEF signal intensity increases quartically with the spot size, which leads to high sensitivity to aberrations that distribute the energy deposition of the focused light¹. For retinal imaging, decreasing the spot size requires the imaging beam to fill a larger area of the eye, which corresponds to an increase in the aberration amplitudes and often results in low TPEF. Recent research has demonstrated improvements to the TPEF signal for retinal imaging using AO for aberrations correction^2,3,4.

Theoretically, the numerical aperture through the pupil of the mouse eye permits sub-micrometer imaging of the retina. However, optical aberrations introduced by the tear film, cornea and intraocular lens reduce the actual resolution. In order to approach diffraction limited imaging, these aberrations can be corrected with Adaptive Optics (AO) using a wavefront corrector such as Deformable Mirror (DM). The traditional approach to AO is to use a Wavefront Sensor (WFS) to measure the ocular aberrations directly. Performing accurate wavefront measurements for WFS AO imaging in a small animal eye requires a high system complexity due to the short length of the eye creating an optically thick sample with multiple scattering surfaces. Alternatively, Sensorless AO (SAO) has the potential to overcome the limitations of the SH-WFS. SAO does not require direct measurement of the optical wavefront but instead uses an image-based approach. SAO methods have the ability to provide depth resolved aberration correction by performing the aberration correction at different layers within the retina.

Our imaging system provides volumetric TPEF imaging in the retina using SAO-OCT for depth-specific aberration correction, using same light source to generate the OCT and TPEF. Here, we present our progress since our previous report4 with improvements to the light delivery, aberration correction, and TPEF detection.

Artificial test eyes have been developed for a multimodal ophthalmic imaging platform. The test eyes can be used for alignment of different imaging modalities and for fluorescence channel performance testing. Different scattering and absorption characteristics can be realized in the artificial retina.

Destructuring of the extracellular matrix has been identified as a key factor in the initial stages of cartilage degeneration. The disruption and reorganisation of the collagen network leads to alterations in the materials intrinsic birefringent properties. A recent study showed that healthy bovine cartilage, that has been compressed and fixed, exhibits stronger birefringence than cartilage with early signs of degeneration. In this summary, we use polarization-sensitive optical coherence tomography (PS-OCT) to dynamically extract such optical properties, in real-time, during an established creep loading protocol. Preliminary results provide an insight into the physiological response of collagen fibers which indicate that the observed birefringence is likely due to the middle and deep zone fiber alignment becoming non-parallel with respect to the propagating light. This finding not only helps explain many of the contradictory findings presented in previous studies but also demonstrates that PS-OCT offers a non-destructive and non-invasive method to gain insight into the complex physiology behind cartilage degeneration in a real-time manner.

In recent years, an emerging group of therapeutic methods, which can be considered as intermediate between photobiomodulation and coagulative methods, is non-surgical thermo-mechanical reshaping of avascular collagenous biological tissues. It is based on moderate laser-produced heating (below 50-70°C) combined with auxiliary mechanical action on the tissue. For duly chosen parameters, such moderate heating can be biologically non-destructive, so that this technique of laser-assisted modification of collagenous tissues is emerging in clinic for various applications. For example, using such an approach, planar cartilaginous plates can be transformed into annulus-shape implants for otolaryngological operations. Similar microstructural changes occurring in moderately heated cornea open the possibility to modify eye-cornea shape and, consequently, eye refraction, which can be used for non-surgical correction of vision problems. Such applications obviously require detailed understanding of the background thermo-mechanical properties and possibility to precisely control the laser-produced heating and the resultant deformations of the tissue. Recently, progress in the development of optical coherence elastography (OCE), in particular the possibility to obtain high-resolution maps of "instantaneous" and cumulative strains suggests that OCE can be successfully used as a control mean in the novel applications of laser-assisted tissue reshaping. This study reports results on application of phase-sensitive optical coherence elastography for mapping transient thermomechanically-produced strain fields in such biological tissues, as cartilages and cornea subjected to pulse-periodic irradiation with infrared Gaussian laser beam. The developed OCE technique made it possible to demonstrate complex character of the thermo-mechanically produced strains, which is attributed to non-trivial interplay between the spatially non-coinciding temperature increase and thermal stresses.

We present a novel phase imaging system based on a non-interferometric approach to obtain the complex amplitude of a wavefront. We sample the wavefront with a high-speed spatial light modulator. Then, a single lens forms a time-dependent light distribution on its focal plane, where a position detector is placed. This simple setup, with the aid of computational techniques, provides high spatial resolution, power efficiency, high dynamic range, and allows to work in spectral regions outside the VIS range. The validity of the technique is demonstrated by measuring both optical aberrations and phase distributions of transparent samples.

Brain tumor is resulting from the development of abnormal cells in the brain, probably leading to headache, vision or mental problems. Currently, surgery is the most effective solution to remove the tumor cells as possible. However, it is difficult to determine the safe margin during brain surgery. In this study, we implement optical coherence tomography (OCT) and OCT angiography (OCTA) to in vivo observe the growth of brain tumor and to evaluate the difference between normal and cancerous brain tissue. A swept-source OCT (SS-OCT) with a center wavelength of 1060 nm was developed for the study of brain tumor on the animal model and the angiographic algorithm was also demonstrated for simultaneously acquiring brain microcirculation. From the results, the change in the morphology of brain tissue during tumor growth can be identified. Moreover, the angiogenesis resulting from tumor growth can be observed. Moreover, the texture of OCT images and the angiogenesis are quantitatively evaluated. It can be noted that OCT/OCTA could be a potential tool for in vivo identification of brain tumor during brain surgery or treatments.

Tattoos can be used in forensic human identification as a secondary means of identification (other means being, but not limited to, personal descriptions and artefacts) allowing the identification procedure to be strengthened in this way. Despite this, the decomposition of tattoos is a topic not extensively studied in taphonomic research (study of how organisms decay). In this communication, we assess optical coherence tomography (OCT) as a method to reliably identify tattoos before and after decomposition, by imaging tattooed porcine samples. OCT was able to penetrate up to 3mm below the surface and visualize parts of tattoos after 16 days of decomposition, which were no longer visible and recognizable using conventional photography-based methods. We believe this imaging modality has the potential to increase the reliability of tattoos in forensic human identification.

The key quality parameters of meat that determine our eating experience are the percentage of intramuscular fat (IMF), the tenderness and the pH of meat. Existing methods to determine the quality of meat are chemical or mechanical which are often slow, destructive and have huge sampling errors. Polarisation sensitive Optical coherence tomography (PS-OCT) is a new fast, non-contact and non-destructive technique with a few microns resolution up to a few millimeters deep in tissues as opaque as meat. We use PS-OCT to measure the attenuation and birefringence of meat samples to determine their IMF content and tenderness. The attenuation of light in fat and muscle was studied to find that the attenuation coefficient in fat is ≈ 9 times greater than in muscle, which provides a way to study and predict the IMF content in meat samples. Also the phase image tells about the changes in the polarisation of light due to the birefringence of muscle, which varies with tenderness and can be analysed to predict the tenderness of meat. To make make prediction models, the OCT results are compared to gas chromatography ame ionization detection (GC-FID) fat estimate and Warner-Bratzler tenderness estimate results.

images. We propose to use 2D Fourier filters in different transform domains including Fourier, wavelet, and nonsubsampled contourlet domains to eliminate this kind of noise. We used image entropy and vessel density as the metrics to evaluate their performance on noise elimination, we found that filtering after the nonsubsampled contourlet transform (NSCT) was the best choice among these approaches. For vessel preservation, the wavelet-domain filtering has the advantage of keeping signal-to-noise ratio while the NSCT filtering can preserve structure similarity to the most extent.

For performance testing of high-resolution label-free optical coherence tomography (OCT) systems, durable test standards with optical properties similar to native biological tissues are highly desirable. Therefore, we explored the establishment of ex-vivo 3D samples from dissected mouse retina. To achieve high stability, dissected tissue parts were embedded in EPON resin. Results from comparative investigations with OCT on murine retina in agarose demonstrate that by utilization of appropriate EPON embedding protocols durable samples with adequate refractive index properties can be created in which even tiny structures near the OCT resolution limits can be detected.

We demonstrate dual-band wavelength-comb-swept laser for solving the aliasing interferometer signal in displacement measurement. Wavelength-comb-swept laser with etalon filter has longer coherence length and narrower linewidth than conventional wavelength-swept laser. On the other hand, aliasing of interferometer signal in displacement measurement is induced because of discrete distribution of comb spectra in wavelength domain. By using the dual-band wavelength-comb-swept-laser which has two different free spectral range (FSR) comb in each band, aliasing interferometer signal can be solved.

We present two versatile and reliable methods of determination of the corneal limbi localization from OCT images. These methods are fully automatic and are based on the purely geometrical dependencies of corneal shape, backgrounded by anatomical structure of the corneoscleral area. The first method enables to estimate the position of the point of corneoscleral junction (CSJ) at the anterior surface of the cornea. The second method can be used for automatic retrieval of the limbal point at the posterior surface of the cornea, which plays an important role in quantification of the irido-corneal angle.

Colonization of microorganisms in removable prosthesis is a recurrent problem, affecting almost the totality of prosthetic patients. In the present study, optical coherence tomography (OCT) was employed to evaluate in vitro the biofilm formation in complete dental prostheses. Four acrylic resins (Coe-Comfort, Soft-Confort, VipiCril Plus and Lucitone 550) were divided into four groups (n = 10), polymerized and polished according to their respective manufacturers’ guidelines. OCT scanning was performed for all samples before and 96 h after inoculation with Candida albicans and Staphylococcus aureus. The employed OCT system (Callisto SD-OCT, Thorlabs Inc.) operates in the Spectral Domain with central wavelength at 930 nm, 100 nm of spectral bandwidth, maximum output power of 5 mW, axial resolution of 7 / 5.3 μm in water / air, respectively, lateral resolution of 8 μm and depth of light penetration of 1.6 mm inside the sample. The biofilm evaluation was carried out in a qualitative/quantitative way through 2D optical images. The formed biofilm was clearly visualized and its thickness measured, besides observation of porosity according to the material employed. The results of the present study suggest that OCT is a viable technique to visualize the biofilm in all types of acrylic resin studied, besides allowing a view of the internal structure of the material and providing porosity data. It has the potential for clinical use in prostheses being used by patients, which are removed for evaluation.

We developed an eye phantom that mimic retinal layers and blood vessels to evaluation of retinal OCT-angiography and fundus angiography. The phantom was made of polydimethylsiloxane and titanium dioxide using spin coater and microelectromechanical system (MEMS) technology.

It is known that Nd:YAG laser radiation on dental structure can increase enamel resistance to demineralization; however, few studies report its impact in orthodontics. This study aimed to verify the interaction of Nd:YAG laser and aluminum oxide sandblasting (Al₂O₃) as preconditioning treatment of lingual brackets bonding to quantify the shear bond strength (SBS) and to characterize the enamel after different surface preconditioning techniques. Thirty-five bovines’ incisors were divided in 5 groups (n=7), according to the preconditioning. All groups had the lingual brackets bonded with Transbond XT adhesive according to manufacturer’ protocol, and shear bonded after 72h. Samples were analyzed by Optical Coherence Tomography (OCT) and Scanning Eletronic Microscope (SEM) to verify enamel alterations. Optical attenuation coefficient (α) was measured before any preconditioning (T0) and after preconditioning surface (T1) for each group. Statistics analysis ANOVA-test was used, followed by Post Hoc Tukey for shear bond strength data, and Kruskal Wallis and post hoc Dunn test for α data. SEM and OCT qualitative analysis showed the melting effect with laser irradiation and enamel crystal surface disorganization with sandblasting in T1 and after shear bond. All groups were adequate for SBS and the statistical differences (p=0.0034) among groups showed better results for groups with techniques association (laser and Al2O3 used in this or in reverse order) and the highest SBS when laser was used after. The Al2O3 removes part of melting effect. The α had statistical difference (p= 0.0124) among groups, increasing with laser and Al2O3 isolated and decrease with techniques association.

We report fabrication and performance of the three-dimensional intraoral scanner based on optical coherence tomography (OCT) that enables three-dimensional structure images of tooth and diagnosis of the tooth through OCT images. The OCT system was configured the swept source OCT (SS-OCT), that is based on the swept source with center wavelength of 1310 nm, the scanner was built using MEMs mirror and optical collimator. The implemented SS-OCT based on MEMs scanner show axial resolution of 10 μm, scan length of 10 mm. With OCT system, OCT 2D images of the human tooth obtained by intraoral scanner based on OCT system. 3D OCT image of the human tooth was obtained by combining the 500 2D OCT images and also included internal information and structure of the human tooth. 3D images of a human tooth obtained were sequentially stitching using the iterative closet point (ICP). By equipping the implemented SS-OCT system with MEMs probe and using ICP algorithm, the intraoral scanner based on OCT system was constructed and used to demonstrate the feasibility of intraoral scanner, that is able to acquire the structure and function images of the human tooth, for intraoral scanner 3D image in dentistry.

An efficient technique for constructing the achromatic phase shift in the reference arm of spectral-domain OCT is presented. The technique is based on a wavelength-dependent optical delay line using a diffractive grating as a dispersive element. The high value of mirror artifact decreasing is demonstrated in common OCT setup.

Wavefront shaping techniques allow one to focus light inside and through turbid media. In order to gain a better understanding how light evolves inside a scattering random medium while shaping the incident wavefront, it is beneficial to know the electromagnetic field within the entire medium, which is difficult to achieve in experiments. Here we investigate wavefront shaping techniques with numerical simulations based on Maxwell's equations to examine various effects of wave propagation in randomly scattering media. First, we calculate numerically monochromatic plane wave solutions for a given scattering medium for different incident k-vectors. With these plane wave solutions we are able to simulate complex-shaped incident wavefronts impinging on the scattering medium. This enables us to scan and tilt the incident complex wavefront after solving Maxwell's equations and to examine the electromagnetic field inside the medium. Due to the fact that we have access to the electromagnetic field of the plane wave illumination from different angles, it is easy to phase-optimize an incident wavefront by conjugating the known phase at a certain location. Because of the separate calculation of the plane wave solutions and the possibility to simulate different incident wavefronts by superimposing these plane wave solutions, our method is very dynamic and versatile. In summary, our simulation approach contributes to the understanding of light propagation in strongly scattering media such as biological tissue and to the improvement of medical imaging techniques.

The present study is concerned with wavefront shaping algorithms and their performance in noisy environments. Simple sequential algorithms has quite low initial enhancement rate which makes it hard to overcome strong noise. As a result, more complex algorithms which use multiple spatial light modulator pixels were developed. It made it possible to overcome noise at the initial stage faster. One of such algorithms is the partitioning algorithm. The maximum length sequence algorithm considered in this paper is proposed as an improvement of the partitioning algorithm. Both algorithms have similar initial enhancement rates but the proposed one keeps higher rate also at later stages.

Optical coherence tomography (OCT) technology can be used to obtain high resolution cross sectional image of living biological tissues. Early study suggested that some tissue optical properties could also be measured using OCT. In this study, OCT was used to measure the total attenuation coefficient of living kidney of rat and dog models. Results suggested that the total attenuation coefficient of the superficial cortex layer could by derived from a single scattering model. The total attenuation coefficient could be affected by ischemia.

An intraoperative diagnosis of brain tumors is one of the most urgent and challenging problem of the modern neurosurgery. The most important measure of the effectiveness of treatment is the complete tumor resection. The existing methods of the intraoperative neurodiagnosis of tumors are plagued with limited sensitivity, especially for low-grade gliomas, and, furthermore, can remain rather expensive. The recently reported results of optical coherence tomography (OCT) application for finding differences between healthy and malignant tissues make it become one of the promising label-free diagnostic instruments. Nevertheless, the wide use of OCT in clinical practice is limited by the lack of complete study of its opportunities in neurosurgery, which leads to a huge scientific interest. Our research, aimed at the study of the ability of OCT for the intraoperative diagnosis of brain gliomas of different grades, has the goal to observe the differences between OCT signals obtained for ex vivo samples of various types of human brain glioma and intact brain tissue. We propose a 3D-feature based data analysis that demonstrates promising results in differentiation of tissue classes.

We study experimentally the operating conditions of a semiconductor laser diode subjected to different amounts of optical feedback in order to find a stable and cost-efficient solution for speckle reduction in double-pass retinal imaging.