Apoptosis- and necrosis-induced changes in light attenuation measured by optical coherence tomography

Line-field dynamic optical coherence tomography platform for volumetric assessment of biological tissues

Dynamic optical coherence tomography (dOCT) utilizes time-dependent signal intensity fluctuations to enhance contrast in OCT images and indirectly probe physiological processes in cells. Majority of the dOCT studies published so far are based on acquisition of 2D images (B-scans or C-scans) by utilizing point-scanning Fourier domain (spectral or swept-source) OCT or full-field OCT respectively, primarily due to limitations in the image acquisition rate. Here we introduce a novel, high-speed spectral domain line-field dOCT (SD-LF-dOCT) system and image acquisition protocols designed for fast, volumetric dOCT imaging of biological tissues. The imaging probe is based on an exchangeable afocal lens pair that enables selection of combinations of transverse resolution (from 1.1 µm to 6.4 µm) and FOV (from 250 × 250 µm2 to 1.4 × 1.4 mm2), suitable for different biomedical applications. The system offers axial resolution of ∼ 1.9 µm in biological tissue, assuming an average refractive index of 1.38. Maximum sensitivity of 90.5 dB is achieved for 3.5 mW optical imaging power at the tissue surface and maximum camera acquisition rate of 2,000 fps. Volumetric dOCT images acquired with the SD-LF-dOCT system from plant tissue (cucumber), animal tissue (mouse liver) and human prostate carcinoma spheroids allow for volumetric visualization of the tissues' cellular and sub-cellular structures and assessment of cellular motility.

Towards non-invasive tissue hydration measurements with optical coherence tomography

The attenuation coefficient ( μ OCT ) measured by optical coherence tomography (OCT) has been used to determine tissue hydration. Previous dual-wavelength OCT systems could not attain the needed precision, which we attribute to the absence of wavelength-dependent scattering of tissue in the underlying model. Assuming that scattering can be described using two parameters, we propose a triple/quadrupole-OCT system to achieve clinically relevant precision in water volume fraction. In this study, we conduct a quantitative analysis to determine the necessary precision of μ OCT measurements and compare it with numerical simulation. Our findings emphasize that achieving a clinically relevant assessment of a 2% water fraction requires determining the attenuation coefficient with a remarkable precision of 0.01 m m - 1 . This precision threshold is influenced by the chosen wavelength for attenuation measurement and can be enhanced through the inclusion of a fourth wavelength range.

Theoretical and experimental determination of the confocal function of OCT systems for accurate calculation of sample optical properties

The attenuation coefficient of biological tissue could serve as an indicator of structural and functional changes related to the onset or progression of disease. Optical coherence tomography (OCT) provides cross sectional images of tissue up to a depth of a few millimeters, based on the local backscatter properties. The OCT intensity also depends on the confocal function, which needs to be characterised to determine correctly the exponential decay of the intensity based on Lambert-Beer. We present a model for the confocal function in scattering media based on the illumination with a Gaussian beam and the power transfer into a single mode fibre (SMF) of the backscattered light for an incoherently back scattered Gaussian beam using the Huygens-Fresnel principle and compare that model with the reflection from a mirror. We find that, contrary to previous literature, the confocal functions characterised by the Rayleigh range in the two models are identical. Extensive OCT focus series measurements on a mirror, Spectralon and Intralipid dilutions confirm our model, and show that for highly scattering samples the confocal function characterised by the Rayleigh range becomes depth dependent. From the diluted Intralipid measurements the attenuation coefficients are extracted using a singly scatter model that includes the previously established confocal function. The extracted attenuation coefficients were in good agreement for weakly scattering samples (μ s  < 2 mm-1).

Phytotoxicity and cytogenotoxicity of pesticide mixtures: analysis of the effects of environmentally relevant concentrations on the aquatic environment

In this study, we investigate the toxicity of commercial formulations based on glyphosate, 2,4-D, imidacloprid, and iprodione, in isolation and mixed, on Allium cepa. The mixtures consisted of combinations in the lowest (M1), intermediate (M2), and highest concentrations (M3) of each pesticide. We measured physiological (germination rate, germination speed, and radicular length) and cyto-genotoxic (mitotic index and frequency of aberrant cells) parameters. In addition, we analyzed the cell cycle progression and cell death induction by flow cytometry. When applied in isolation, the pesticides changed the parameters evaluated. M1 and M2 inhibited root length and increased the frequency of aberrant cells. Their genotoxic effect was equivalent to that of pesticides applied in isolation. Furthermore, M1 and M2 caused cell death and M2 changed the cell cycle progression. M3 had the greatest deleterious effect on A. cepa. This mixture inhibited root length and promoted an additive or synergistic effect on the mitotic index. In addition, M3 changed all parameters analyzed by flow cytometry. This research clearly demonstrates that the pesticides tested, and their mixtures, may pose a risk to non-target organisms.

Dynamic optical coherence tomography for cell analysis [Invited]

Label-free live optical imaging of dynamic cellular and subcellular features has been made possible in recent years thanks to the advances made in optical imaging techniques, including dynamic optical coherence tomography (D-OCT) methods. These techniques analyze the temporal fluctuations of an optical signal associated with the active movements of intracellular organelles to obtain an ensemble metric recapitulating the motility and metabolic state of cells. They hence enable visualization of cells within compact, static environments and evaluate their physiology. These emerging microscopies show promise, in particular for the three-dimensional evaluation of live tissue samples such as freshly excised biopsies and 3D cell cultures. In this review, we compare the various techniques used for dynamic OCT. We give an overview of the range of applications currently being explored and discuss the future outlook and opportunities for the field.

The impacts of resveratrol on the retinal degeneration in a rat model of retinitis pigmentosa induced by alkylation: an in-vivo study

Upregulation of Sirtuin Type 1 (SIRT1), a nicotinamide adeninedinucleotide (NAD⁺)-dependent deacetylase, has been proved to protect against ample ocular diseases, while its effect on retinitis pigmentosa (RP) has not been illustrated. The study was aimed to explore the impacts of resveratrol (RSV), a SIRT1 activator, on the photoreceptor degeneration in a rat model of RP induced by N-methyl-N-nitrosourea (MNU), an alkylation. The rats were induced RP phenotypes via the intraperitoneal injection of MNU. The electroretinogram was conducted and revealed that RSV could not prevent the decline of retinal function in the RP rats. The optical coherence tomography (OCT) and the retinal histological examination were performed and showed that the reduced thickness of the outer nuclear layer (ONL) was not preserved by RSV intervention. The immunostaining technique was applied. Afther the MNU administration, the number of the apoptotic photoreceptors in the ONL throughout the retinasand the number of microglia cells present among the outer part throughout the retinas were not significantly reduced by RSV. Western blotting was also performed. The data showed that the level of SIRT1 protein was decreased after MNU administration, while RSV was not able to obviously alleviate the downregulation. Our data together indicated that RSV was not able to rescue the photoreceptor degeneration in the MNU-induced RP rats, which might be due to the MNU-induced consumption of the NAD⁺.

Multiparametric Quantitative Analysis of Photodamage to Skin Using Optical Coherence Tomography

Ultraviolet (UV) irradiation causes 90% of photodamage to skin and long-term exposure to UV irradiation is the largest threat to skin health. To study the mechanism of UV-induced photodamage and the repair of sunburnt skin, the key problem to solve is how to non-destructively and continuously evaluate UV-induced photodamage to skin. In this study, a method to quantitatively analyze the structural and tissue optical parameters of artificial skin (AS) using optical coherence tomography (OCT) was proposed as a way to non-destructively and continuously evaluate the effect of photodamage. AS surface roughness was achieved based on the characteristic peaks of the intensity signal of the OCT images, and this was the basis for quantifying AS cuticle thickness using Dijkstra's algorithm. Local texture features within the AS were obtained through the gray-level co-occurrence matrix method. A modified depth-resolved algorithm was used to quantify the 3D scattering coefficient distribution within AS based on a single-scattering model. A multiparameter assessment of AS photodamage was carried out, and the results were compared with the MTT experiment results and H&E staining. The results of the UV photodamage experiments showed that the cuticle of the photodamaged model was thicker (56.5%) and had greater surface roughness (14.4%) compared with the normal cultured AS. The angular second moment was greater and the correlation was smaller, which was in agreement with the results of the H&E staining microscopy. The angular second moment and correlation showed a good linear relationship with the UV irradiation dose, illustrating the potential of OCT in measuring internal structural damage. The tissue scattering coefficient of AS correlated well with the MTT results, which can be used to quantify the damage to the bioactivity. The experimental results also demonstrate the anti-photodamage efficacy of the vitamin C factor. Quantitative analysis of structural and tissue optical parameters of AS by OCT enables the non-destructive and continuous detection of AS photodamage in multiple dimensions.

Deep learning-based optical coherence tomography image analysis of human brain cancer

Real-time intraoperative delineation of cancer and non-cancer brain tissues, especially in the eloquent cortex, is critical for thorough cancer resection, lengthening survival, and improving quality of life. Prior studies have established that thresholding optical attenuation values reveals cancer regions with high sensitivity and specificity. However, threshold of a single value disregards local information important to making more robust predictions. Hence, we propose deep convolutional neural networks (CNNs) trained on labeled OCT images and co-occurrence matrix features extracted from these images to synergize attenuation characteristics and texture features. Specifically, we adapt a deep ensemble model trained on 5,831 examples in a training dataset of 7 patients. We obtain 93.31% sensitivity and 97.04% specificity on a holdout set of 4 patients without the need for beam profile normalization using a reference phantom. The segmentation maps produced by parsing the OCT volume and tiling the outputs of our model are in excellent agreement with attenuation mapping-based methods. Our new approach for this important application has considerable implications for clinical translation.

Precision of attenuation coefficient measurements by optical coherence tomography

SIGNIFICANCE

Optical coherence tomography (OCT) is an interferometric imaging modality, which provides tomographic information on the microscopic scale. Furthermore, OCT signal analysis facilitates quantification of tissue optical properties (e.g., the attenuation coefficient), which provides information regarding the structure and organization of tissue. However, a rigorous and standardized measure of the precision of the OCT-derived optical properties, to date, is missing.

AIM

We present a robust theoretical framework, which provides the Cramér -Rao lower bound σμOCT for the precision of OCT-derived optical attenuation coefficients.

APPROACH

Using a maximum likelihood approach and Fisher information, we derive an analytical solution for σμOCT when the position and depth of focus are known. We validate this solution, using simulated OCT signals, for which attenuation coefficients are extracted using a least-squares fitting procedure.

RESULTS

Our analytical solution is in perfect agreement with simulated data without shot noise. When shot noise is present, we show that the analytical solution still holds for signal-to-noise ratios (SNRs) in the fitting window being above 20 dB. For other cases (SNR&lt;20 dB, focus position not precisely known), we show that the numerical calculation of the precision agrees with the σμOCT derived from simulated signals.

CONCLUSIONS

Our analytical solution provides a fast, rigorous, and easy-to-use measure for OCT-derived attenuation coefficients for signals above 20 dB. The effect of uncertainties in the focal point position on the precision in the attenuation coefficient, the second assumption underlying our analytical solution, is also investigated by numerical calculation of the lower bounds. This method can be straightforwardly extended to uncertainty in other system parameters.

Label-free, non-invasive, and repeatable cell viability bioassay using dynamic full-field optical coherence microscopy and supervised machine learning

We present a novel method that can assay cellular viability in real-time using supervised machine learning and intracellular dynamic activity data that is acquired in a label-free, non-invasive, and non-destructive manner. Cell viability can be an indicator for cytology, treatment, and diagnosis of diseases. We applied four supervised machine learning models on the observed data and compared the results with a trypan blue assay. The cell death assay performance by the four supervised models had a balanced accuracy of 93.92 ± 0.86%. Unlike staining techniques, where criteria for determining viability of cells is unclear, cell viability assessment using machine learning could be clearly quantified.

Characterization and identification of cell death dynamics by quantitative phase imaging

SIGNIFICANCE

Investigating cell death dynamics at the single-cell level plays an essential role in biological research. Quantitative phase imaging (QPI), a label-free method without adverse effects of exogenous labels, has been widely used to image many types of cells under various conditions. However, the dynamics of QPI features during cell death have not been thoroughly characterized.

AIM

We aim to develop a label-free technique to quantitatively characterize single-cell dynamics of cellular morphology and intracellular mass distribution of cells undergoing apoptosis and necrosis.

APPROACH

QPI was used to capture time-lapse phase images of apoptotic, necrotic, and normal cells. The dynamics of morphological and QPI features during cell death were fitted by a sigmoid function to quantify both the extent and rate of changes.

RESULTS

The two types of cell death mainly differed from normal cells in the lower phase of the central region and differed from each other in the sharp nuclear boundary shown in apoptotic cells.

CONCLUSIONS

The proposed method characterizes the dynamics of cellular morphology and intracellular mass distributions, which could be applied to studying cells undergoing state transition such as drug response.

Multiphysical numerical study of photothermal therapy of glioblastoma with photoacoustic temperature monitoring in a mouse head

This paper presents a multiphysical numerical study of a photothermal therapy performed on a numerical phantom of a mouse head containing a glioblastoma. The study has been designed to be as realistic as possible. Heat diffusion simulations were performed on the phantom to understand the temperature evolution in the mouse head and therefore in the glioblastoma. The thermal dose has been calculated and lesions caused by heat are shown. The thermal damage on the tumor has also been quantified. To improve the effectiveness of the therapy, the photoabsorber's concentration was increased locally, at the tumor site, to mimic the effect of using absorbing contrast agents such as nanoparticles. Photoacoustic simulations were performed in order to monitor temperature in the phantom: as the Grüneisen parameter changes with the temperature, the photoacoustic signal undergoes changes that can be linked to temperature evolution. These photoacoustic simulations were performed at different instants during the therapy and the evolution of the photoacoustic signal as a function of the spatio-temporal distribution of the temperature in the phantom was observed and quantified. We have developed in this paper a numerical tool that can be used to help defining key parameters of a photothermal therapy.

Tumor radiosensitization by photobiomodulation

PURPOSE

To investigate the safety of photobiomodulation therapy (PBM) in tumors and its potential as a radiosensitizer when combined with radiotherapy.

METHODS

We have performed in vitro experiments in A431 cells to assess proliferation and cell cycle after PBM, as well as clonogenic assay and H2AX-gamma immunolabeling to quantify double strand breaks after the combination of PBM and radiation. In vivo experiments in xenografts included Kaplan-Meier survival analysis, optical coherence tomography (OCT) and histological analysis.

RESULTS

PBM did not induce proliferation in vitro, but increased the G2/M fraction by 27% 24h after illumination, resulting in an enhancement of 30% in radiation effect in the clonogenic assay. The median survival of the PBM-RT group increased by 4 days and the hazard ratio was 0.417 (CI 95%: 0.173-1.006) when compared to radiation alone. OCT analysis over time demonstrated that PBM increases tumor necrosis due to radiation, and histological analysis showed that illumination increased cell differentiation and angiogenesis, which may play a role in the synergetic effect of PBM and radiation.

CONCLUSION

PBM technique may be one of the most appropriate approaches for radiosensitizing tumors while protecting normal tissue because of its low cost and low training requirements for staff.

Label-free functional and structural imaging of liver microvascular complex in mice by Jones matrix optical coherence tomography

We demonstrate label-free imaging of the functional and structural properties of microvascular complex in mice liver. The imaging was performed by a custom-built Jones-matrix based polarization sensitive optical coherence tomography (JM-OCT), which is capable of measuring tissue's attenuation coefficient, birefringence, and tiny tissue dynamics. Two longitudinal studies comprising a healthy liver and an early fibrotic liver model were performed. In the healthy liver, we observed distinctive high dynamics beneath the vessel at the initial time point (0 h) and reappearance of high dynamics at 32-h time point. In the early fibrotic liver model, we observed high dynamics signal that reveals a clear network vascular structure by volume rendering. Longitudinal time-course imaging showed that these high dynamics signals faded and decreased over time.

Quantitative evaluation of the dynamic activity of HeLa cells in different viability states using dynamic full-field optical coherence microscopy

Dynamic full-field optical coherence microscopy (DFFOCM) was used to characterize the intracellular dynamic activities and cytoskeleton of HeLa cells in different viability states. HeLa cell samples were continuously monitored for 24 hours and compared with histological examination to confirm the cell viability states. The averaged mean frequency and magnitude observed in healthy cells were 4.79±0.5 Hz and 2.44±1.06, respectively. In dead cells, the averaged mean frequency was shifted to 8.57±0.71 Hz, whereas the magnitude was significantly decreased to 0.53±0.25. This cell dynamic activity analysis using DFFOCM is expected to replace conventional time-consuming and biopsies-required histological or biochemical methods.

In vivo optical coherence tomography-guided photodynamic therapy for skin pre-cancer and cancer

BACKGROUND

The primary aim of this prospective study is to demonstrate the technical feasibility of OCT to map real tumor margins and to monitor skin changes that occurred post- PDT. Moreover, to optimize PDT efficacy based on the relationship between measured OCT features and treatment outcome.

MATERIAL AND METHODS

A series of 12 patients with overall 18 facial skin lesions were investigated by OCT before surface illumination by PDT to determine tumor free margins. Monitoring of the healing process was undertaken at 3, 6 and 12 months post-PDT. Parameters measured by the in vivo OCT during healing phase were the organization of skin layer and the degree skin fibroses for the active center and peripheral transit zone of the treated lesion. Clinical and aesthetics assessment was carried out at 12-month post-PDT.

RESULTS

Distinct microstructural differences between normal skin, pre-cancer, cancer, and the transition zone between the two tissues were observed on OCT images. In the subsequent healing phase, OCT demonstrate marked delineation and organization of skin layer at late stage of healing. Early features showing bizarre non-homogenous disorganized layering (scab) but afterwards, OCT was able to differentiate between different histological layers. One lesion demonstrated clinical healing by fibrosis (scar) without sign of recurrence. Another lesion demonstrated skin erythema. Only one lesion did not response to treatment despite margins clearance. The CR rate was 95% at the end of the study. The cosmetic effect was "excellent" in 89% of the patients.

CONCLUSIONS

This feasibility study lays the groundwork for using OCT as a real-time, noninvasive monitoring device for PDT in patients with skin cancer.

Volumetric tumor delineation and assessment of its early response to radiotherapy with optical coherence tomography

Texture analyses of optical coherence tomography (OCT) images have shown initial promise for differentiation of normal and tumor tissues. This work develops a fully automatic volumetric tumor delineation technique employing quantitative OCT image speckle analysis based on Gamma distribution fits. We test its performance in-vivo using immunodeficient mice with dorsal skin window chambers and subcutaneously grown tumor models. Tumor boundaries detection is confirmed using epi-fluorescence microscopy, combined photoacoustic-ultrasound imaging, and histology. Pilot animal study of tumor response to radiotherapy demonstrates high accuracy, objective nature, novelty of the proposed method in the volumetric separation of tumor and normal tissues, and the sensitivity of the fitting parameters to radiation-induced tissue changes. Overall, the developed methodology enables hitherto impossible longitudinal studies for detecting subtle tissue alterations stemming from therapeutic insult.

Submicron spatial resolution optical coherence tomography for visualising the 3D structures of cells cultivated in complex culture systems

Three-dimensional (3D) configuration of in vitro cultivated cells has been recognised as a valuable tool in developing stem cell and cancer cell therapy. However, currently available imaging approaches for live cells have drawbacks, including unsatisfactory resolution, lack of cross-sectional and 3D images, and poor penetration of multi-layered cell products, especially when cells are cultivated on semitransparent carriers. Herein, we report a prototype of a full-field optical coherence tomography (FF-OCT) system with isotropic submicron spatial resolution in en face and cross-sectional views that provides a label-free, non-invasive platform with high-resolution 3D imaging. We validated the imaging power of this prototype by examining (1) cultivated neuron cells (N2A cell line); (2) multilayered, cultivated limbal epithelial sheets (mCLESs); (3) neuron cells (N2A cell line) and mCLESs cultivated on a semitransparent amniotic membrane (stAM); and (4) directly adherent colonies of neuron-like cells (DACNs) covered by limbal epithelial cell sheets. Our FF-OCT exhibited a penetrance of up to 150 μm in a multilayered cell sheet and displayed the morphological differences of neurons and epithelial cells in complex coculture systems. This FF-OCT is expected to facilitate the visualisation of cultivated cell products in vitro and has a high potential for cell therapy and translational medicine research.

Parametric imaging of attenuation by optical coherence tomography: review of models, methods, and clinical translation

SIGNIFICANCE

Optical coherence tomography (OCT) provides cross-sectional and volumetric images of backscattering from biological tissue that reveal the tissue morphology. The strength of the scattering, characterized by an attenuation coefficient, represents an alternative and complementary tissue optical property, which can be characterized by parametric imaging of the OCT attenuation coefficient. Over the last 15 years, a multitude of studies have been reported seeking to advance methods to determine the OCT attenuation coefficient and developing them toward clinical applications.

AIM

Our review provides an overview of the main models and methods, their assumptions and applicability, together with a survey of preclinical and clinical demonstrations and their translation potential.

RESULTS

The use of the attenuation coefficient, particularly when presented in the form of parametric en face images, is shown to be applicable in various medical fields. Most studies show the promise of the OCT attenuation coefficient in differentiating between tissues of clinical interest but vary widely in approach.

CONCLUSIONS

As a future step, a consensus on the model and method used for the determination of the attenuation coefficient is an important precursor to large-scale studies. With our review, we hope to provide a basis for discussion toward establishing this consensus.

Protection of retinal function and morphology in MNU-induced retinitis pigmentosa rats by ALDH2: an in-vivo study

Background

Retinitis pigmentosa (RP) is a kind of inherited retinal degenerative diseases characterized by the progressive loss of photoreceptors. RP has been a conundrum without satisfactory countermeasures in clinic until now. Acetaldehyde dehydrogenase 2 (ALDH2), a major enzyme involved in aldehyde detoxification, has been demonstrated to be beneficial for a growing number of human diseases, such as cardiovascular dysfunction, diabetes mellitus and neurodegeneration. However, its protective effect against RP remains unknown. Our study explored the impact of ALDH2 on retinal function and structure in N-methyl-N-nitrosourea (MNU)-induced RP rats.

Methods

Rats were gavaged with 5 mg/kg Alda-1, an ALDH2 agonist, 5 days before and 3 days after MNU administration. Assessments of retinal function and morphology as well as measurement of specific proteins expression level were conducted.

Results

Electroretinogram recordings showed that Alda-1 administration alleviated the decrease in amplitude caused by MNU, rendering protection of retinal function. Mitigation of photoreceptor degeneration in MNU-treated retinas was observed by optical coherence tomography and retinal histological examination. In addition, Western blotting results revealed that ALDH2 protein expression level was upregulatedwith increased expression of SIRT1 protein after the Alda-1 intervention. Besides, endoplasmic reticulum stress (ERS) was reduced according to the significant downregulation of GRP78 protein, while apoptosis was ameliorated as shown by the decreased expression of PARP1 protein.

Conclusions

Together, our data demonstrated that ALDH2 could provide preservation of retinal function and morphology against MNU-induced RP, with the underlying mechanism at least partly related to the modulation of SIRT1, ERS and apoptosis.

Review of methods and applications of attenuation coefficient measurements with optical coherence tomography

The optical attenuation coefficient (AC), an important tissue parameter that measures how quickly incident light is attenuated when passing through a medium, has been shown to enable quantitative analysis of tissue properties from optical coherence tomography (OCT) signals. Successful extraction of this parameter would facilitate tissue differentiation and enhance the diagnostic value of OCT. In this review, we discuss the physical and mathematical basis of AC extraction from OCT data, including current approaches used in modeling light scattering in tissue and in AC estimation. We also report on demonstrated clinical applications of the AC, such as for atherosclerotic tissue characterization, malignant lesion detection, and brain injury visualization. With current studies showing AC analysis as a promising technique, further efforts in the development of methods to accurately extract the AC and to explore its potential use for more extensive clinical applications are desired.

Optical coherence tomography complements confocal microscopy for investigation of multicellular tumour spheroids

Knowledge of optical properties, such as the refractive index (RI), of biological tissues is important in optical imaging, as they influence the distribution and propagation of light in tissue. To accurately study the response of cancerous cells to drugs, optimised imaging protocols are required. This study uses a simple custom-built spectral domain optical coherence tomography (OCT) system to conduct RI measurements of multicellular spheroids, three-dimensional (3D) in-vitro culture systems, of the cell line HCT116. The spheroid RIs are compared to study the effect of growth over time. To improve confocal microscopy imaging protocols, two immersion media (glycerol and ScaleView-A2) matching the spheroid RIs were trialled, with the aim to reduce the RI mismatch between the spheroid and the immersion medium and thus improve imaging depth with confocal microscopy. ScaleView-A2 (n = 1.380) aided in achieving greater depths of imaging of the multicellular spheroids under confocal microscopy. This improvement in imaging depth confirmed the utility of our RI measurements, proving the promising outlook of OCT as a complementary tool to microscopy in cancer research.

Optimized depth-resolved estimation to measure optical attenuation coefficients from optical coherence tomography and its application in cerebral damage determination

The optical attenuation coefficient (OAC) reflects the optical properties of various tissues or tissues of the same type under different physiological conditions. Quantitative measurement of OAC from optical coherence tomography (OCT) signals can provide additional information and can increase the potential for OCT applications. We present an optimized depth-resolved estimation (ODRE) method that derives a precise mapping between the measured OCT signal and the OAC. In contrast to previous depth-resolved estimation (DRE) methods, the optimized method can estimate the OAC in any depth range and ignore whether the light is completely attenuated. Numerical simulations and phantom experiments are used to verify its validity, and this method is applied to detect cerebral damage. In combination with OCT angiography, real-time observation of the change of blood perfusion and the degree of cerebral damage in mice with focal cerebral ischemia provides important information to help us understand the temporal relationship between brain damage and ischemia.

Quantitative assessment of regional variation in tissue clearing efficiency using optical coherence tomography (OCT) and magnetic resonance imaging (MRI): A feasibility study

Tissue clearing has gained attention as a pioneering research tool for imaging of large tissue samples. This technique improves light transmission by reducing light scattering within tissues, either by removing lipids or by replacing water with a high refractive index solution. Although various clearing techniques have been developed, quantitative assessments on clearing efficacy depending on tissue properties are rare. In this study, we developed the quantitative mapping of regional clearing efficacy using mean free path in optical coherence tomography (OCT) and proton density in magnetic resonance imaging (MRI), and demonstrated its feasibility in the brain sample with four representative clearing techniques (benzyl alcohol and benzyl benzoate [BABB], Clear^T, Scale, and passive CLARITY technique [PACT]). BABB (solvent-based clearing), involving both refractive index matching and lipid removal, exhibited best optical clearing performance with the highest proton density reduction both in gray and white matter. Lipid-removing techniques such as Scale (aqueous hyperhydration) and PACT (hydrogel embedding) showed higher clearing efficiency in white matter than gray matter in accordance with larger proton density increase in white matter. For Clear^T (aqueous-based simple immersion), we observed lowest clearing efficiency in the white matter as well as poor lipid removal reflected in low proton density reduction. Our results showed the feasibility of the regional mapping of clearing efficacy and correlating optical transparency and proton density changes using OCT and MRI from existing tissue clearing techniques. This novel quantitative mapping of clearing efficacy depending on tissue types and clearing methods may be helpful in the development of optimized clearing methods for different biological samples.

Review of optical coherence tomography in oncology

The application of optical coherence tomography (OCT) in the field of oncology has been prospering over the past decade. OCT imaging has been used to image a broad spectrum of malignancies, including those arising in the breast, brain, bladder, the gastrointestinal, respiratory, and reproductive tracts, the skin, and oral cavity, among others. OCT imaging has initially been applied for guiding biopsies, for intraoperatively evaluating tumor margins and lymph nodes, and for the early detection of small lesions that would often not be visible on gross examination, tasks that align well with the clinical emphasis on early detection and intervention. Recently, OCT imaging has been explored for imaging tumor cells and their dynamics, and for the monitoring of tumor responses to treatments. This paper reviews the evolution of OCT technologies for the clinical application of OCT in surgical and noninvasive interventional oncology procedures and concludes with a discussion of the future directions for OCT technologies, with particular emphasis on their applications in oncology.

Attenuation Coefficients From SD-OCT Data: Structural Information Beyond Morphology on RNFL Integrity in Glaucoma

PURPOSE

The purpose of this study is to explore the attenuation coefficient (AC) of the retinal nerve fiber layer (RNFL) in spectral domain optical coherence tomography (OCT) images, in healthy eyes and eyes affected by glaucoma. To assess the relation between RNLF AC, disease severity, RNFL thickness, visual field sensitivity threshold, spatial location and age.

PATIENTS AND METHODS

We analyzed peripapillary circle scans of a clinical OCT device (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany) in 102 glaucoma patients and 90 healthy controls. The images were fully automatically converted into depth-resolved AC images. Next, the median AC within the RNFL was calculated based on the Spectralis segmentation. We compared the RNFL AC between healthy, mild, moderate and advanced glaucomatous eyes and assessed the correlation with patient characteristics such as age and visual field sensitivity threshold (HFA, Carl Zeiss Meditec, Dublin, CA) in a generalized estimating equations (GEE) model. Finally, we explored the ability to discriminate between glaucomatous and healthy eyes by RNFL AC.

RESULTS

Median RNFL AC decreased with increasing disease severity up to moderate glaucoma (P<0.001) in all 4 sectors around the optic nerve head. The largest relative decrease occurred in the nasal sector. The RNFL AC (AUC, 0.834±0.028) effectively discriminated healthy from glaucomatous eyes, although RNFL thickness (AUC, 0.975±0.013) performed even better (P<0.001). Prediction of visual field sensitivity improved significantly when RNFL thickness was augmented with RNFL AC as covariates (P<0.001).

CONCLUSIONS

This study demonstrated that RNFL AC provides complementary information on the RNFL's health compared with RNFL thickness measurements alone.

Quantitative analysis of retinal layers on three-dimensional spectral-domain optical coherence tomography for pituitary adenoma

PURPOSE

To quantitatively investigate the characteristics of eyes with pituitary adenoma presented by three-dimensional (3D) spectral-domain optical coherence tomography (SD-OCT) using three common indices, including thickness, optical intensity ratio, and optical intensity attenuation coefficient (OIAC).

METHODS

The SD-OCT database of 38 patients with pituitary adenoma and 39 normal controls were included in the study. Quadrantal and average measurements of thickness, optical intensity ratio, and OIAC were calculated for macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL) combined with inner plexiform layer (IPL) (GCIPL) and/or the collective ganglion cell complex (GCC). The parameters of patients and controls were compared by unpaired t-test and Mann-Whitney U-test. The relationships between the optical intensity ratio and the thickness of mRNFL and GCIPL were evaluated by Pearson's correlation. Diagnostic performances of these indices were assessed using receiver operating characteristic (ROC) analysis.

RESULTS

Significant decreases in thickness existed in the mRNFL and nasal GCC of patients compared with controls (p-values of 0.000 to 0.039). Optical intensity ratios in the relevant retinal layers of patients were almost all lower than those of controls. In patients, optical intensities were increased in the mRNFL but decreased in the GCIPL along with an increase of retinal thicknesses. The OIAC measurements were significantly higher in the upper quadrants and global average of the mRNFL in patients. The areas under the ROC curves (AUC) obtained by global average mRNFL thickness was significantly greater than that of the global average OIAC in the mRNFL (p = 0.0265).

CONCLUSIONS

Thicknesses of the mRNFL and nasal GCC were significantly decreased in the retinas of patients with pituitary adenoma compared with controls. The differences of the optical intensity ratio and OIAC between patients and controls were not all statistically significant. Thickness was more sensitive than optical characteristics indices in distinguishing pituitary adenoma from controls.

Investigation of optical attenuation imaging using optical coherence tomography for monitoring of scars undergoing fractional laser treatment

We demonstrate the use of the near-infrared attenuation coefficient, measured using optical coherence tomography (OCT), in longitudinal assessment of hypertrophic burn scars undergoing fractional laser treatment. The measurement method incorporates blood vessel detection by speckle decorrelation and masking, and a robust regression estimator to produce 2D en face parametric images of the attenuation coefficient of the dermis. Through reliable co-location of the field of view across pre- and post-treatment imaging sessions, the study was able to quantify changes in the attenuation coefficient of the dermis over a period of ∼20 weeks in seven patients. Minimal variation was observed in the mean attenuation coefficient of normal skin and control (untreated) mature scars, as expected. However, a significant decrease (13 ± 5%, mean ± standard deviation) was observed in the treated mature scars, resulting in a greater distinction from normal skin in response to localized damage from the laser treatment. By contrast, we observed an increase in the mean attenuation coefficient of treated (31 ± 27%) and control (27 ± 20%) immature scars, with numerical values incrementally approaching normal skin as the healing progressed. This pilot study supports conducting a more extensive investigation of OCT attenuation imaging for quantitative longitudinal monitoring of scars. En face 2D OCT attenuation coefficient map of a treated immature scar derived from the pre-treatment (top) and the post-treatment (bottom) scans. (Vasculature (black) is masked out.) The scale bars are 0.5 mm.

Assesment of apoptosis induced changes in scattering using optical coherence tomography

The aim of this study is to identify changes in scattering with optical coherence tomography (OCT) and relate these measurements with mitochondrial changes during the initiation of apoptosis. Human retinal pigment epithelial cells were cultured and apoptosis was induced using 10% alcohol. Using the attenuation coefficient and backscattering, changes were measured during cell death in a cell-pellet and monolayer respectively. To confirm apoptosis, fluorescent activated cell sorting was used. Mitochondrial activity during apoptosis was assessed using an oxidative stress assay and fluorescent confocal microscopy. Pelleted apoptotic cells measured with OCT showed a clear rise while untreated cells showed a very small increase in attenuation coefficient. Monolayered apoptotic cells displayed a distinct increase, while untreated cells showed a small increase in the backscattering. Apoptosis was confirmed by FACS experiments. Mitochondrial changes during the onset of apoptosis were also measured. The results demonstrate that apoptotic cell death could be monitored in real-time by OCT. Changes in the scattering after induction of apoptosis are likely to be related to changes in the intracellular morphology. Oxidative stress-induced mitochondrial swelling could be responsible for the initial increase, while cell blebbing and secondary necrosis subsequently for the observed decrease in scattering.

Detection of human brain cancer infiltration ex vivo and in vivo using quantitative optical coherence tomography

More complete brain cancer resection can prolong survival and delay recurrence. However, it is challenging to distinguish cancer from noncancer tissues intraoperatively, especially at the transitional, infiltrative zones. This is especially critical in eloquent regions (for example, speech and motor areas). This study tested the feasibility of label-free, quantitative optical coherence tomography (OCT) for differentiating cancer from noncancer in human brain tissues. Fresh ex vivo human brain tissues were obtained from 32 patients with grade II to IV brain cancer and 5 patients with noncancer brain pathologies. On the basis of volumetric OCT imaging data, pathologically confirmed brain cancer tissues (both high- and low-grade) had significantly lower optical attenuation values at both cancer core and infiltrated zones when compared with noncancer white matter, and OCT achieved high sensitivity and specificity at an attenuation threshold of 5.5 mm(-1) for brain cancer patients. We also used this attenuation threshold to confirm the intraoperative feasibility of performing in vivo OCT-guided surgery using a murine model harboring human brain cancer. Our OCT system was capable of processing and displaying a color-coded optical property map in real time at a rate of 110 to 215 frames per second, or 1.2 to 2.4 s for an 8- to 16-mm(3) tissue volume, thus providing direct visual cues for cancer versus noncancer areas. Our study demonstrates the translational and practical potential of OCT in differentiating cancer from noncancer tissue. Its intraoperative use may facilitate safe and extensive resection of infiltrative brain cancers and consequently lead to improved outcomes when compared with current clinical standards.

Optical coherence tomography accurately identifies patients with penile (pre) malignant lesions: A single center prospective study

Introduction:

Currently, (multiple) biopsies are taken to obtain histopathological diagnosis of suspicious lesions of the penile skin. Optical coherence tomography (OCT) provides noninvasive in vivo images from which epidermal layer thickness and attenuation coefficient (μ_oct) can be quantified. We hypothesize that qualitative (image assessment) and quantitative (epidermal layer thickness and attenuation coefficient, μ_oct) analysis of penile skin with OCT is possible and may differentiate benign penile tissue from (pre) malignant penile tissue.

Materials and Methods:

Optical coherence tomography-imaging was performed prior to punch biopsy in 18 consecutive patients with a suspicious lesion at the outpatient clinic of the NKI-AVL. Qualitative analysis consisted of visual assessment of clear layers and a visible lower border of the lesions, quantitative analysis comprised of determination of the epidermal layer thickness and μ_oct. Results were grouped according to histopathology reports.

Results:

Qualitative analysis showed a statistically significant difference (P = 0.047) between benign and (pre) malignant lesions. Quantitative analysis showed that epidermal layer thickness and attenuation coefficient was significantly different between benign and (pre) malignant tissue, respectively, P = 0.001 and P < 0.001.

Conclusion:

In this preliminary study, qualitative and quantitative analysis of OCT-images of suspicious penile lesions shows differences between benign lesions and (pre) malignant lesions. These results encourage further research in a larger study population.

Optical coherence tomography spectral analysis for detecting apoptosis in vitro and in vivo

Apoptosis is a form of programmed cell death characterized by a series of predictable morphological changes at the subcellular level, which modify the light-scattering properties of cells. We present a spectroscopic optical coherence tomography (OCT) technique to detect changes in subcellular morphology related to apoptosis in vitro and in vivo. OCT data were acquired from acute myeloid leukemia (AML) cells treated with cisplatin over a 48-h period. The backscatter spectrum of the OCT signal acquired from the cell samples was characterized by calculating its in vitro integrated backscatter (IB) and spectral slope (SS). The IB increased with treatment duration, while the SS decreased, with the most significant changes occurring after 24 to 48 h of treatment. These changes coincided with striking morphological transformations in the cells and their nuclei. Similar trends in the spectral parameter values were observed in vivo in solid tumors grown from AML cells in mice, which were treated with chemotherapy and radiation. Our results provide a strong foundation from which future experiments may be designed to further understand the effect of cellular morphology and kinetics of apoptosis on the OCT signal and demonstrate the feasibility of using this technique in vivo.

Longitudinal label-free tracking of cell death dynamics in living engineered human skin tissue with a multimodal microscope

We demonstrate real-time, longitudinal, label-free tracking of apoptotic and necrotic cells in living tissue using a multimodal microscope. The integrated imaging platform combines multi-photon microscopy (MPM, based on two-photon excitation fluorescence), optical coherence microscopy (OCM), and fluorescence lifetime imaging microscopy (FLIM). Three-dimensional (3-D) co-registered images are captured that carry comprehensive information of the sample, including structural, molecular, and metabolic properties, based on light scattering, autofluorescence intensity, and autofluorescence lifetime, respectively. Different cell death processes, namely, apoptosis and necrosis, of keratinocytes from different epidermal layers are longitudinally monitored and investigated. Differentiation of the two cell death processes in a complex living tissue environment is enabled by quantitative image analysis and high-confidence classification processing based on the multidimensional, cross-validating imaging data. These results suggest that despite the limitations of each individual label-free modality, this multimodal imaging approach holds the promise for studies of different cell death processes in living tissue and in vivo organs.

Optical coherence tomography: a new strategy to image planarian regeneration

The planarian is widely used as a model for studying tissue regeneration. In this study, we used optical coherence tomography (OCT) for the real-time, high-resolution imaging of planarian tissue regeneration. Five planaria were sliced transversely to produce 5 head and 5 tail fragments. During a 2-week regeneration period, OCT images of the planaria were acquired to analyze the signal attenuation rates, intensity ratios, and image texture features (including contrast, correlation, homogeneity, energy, and entropy) to compare the primitive and regenerated tissues. In the head and tail fragments, the signal attenuation rates of the regenerated fragments decreased from −0.2 dB/μm to −0.05 dB/μm, between Day 1 and Day 6, and then increased to −0.2 dB/μm on Day 14. The intensity ratios decreased to approximately 0.8 on Day 6, and increased to between 0.8 and 0.9 on Day 14. The texture parameters of contrast, correlation, and homogeneity exhibited trends similar to the signal attenuation rates and intensity ratios during the planarian regeneration. The proposed OCT parameters might provide biological information regarding cell apoptosis and the formation of a mass of new cells during planarian regeneration. Therefore, OCT imaging is a potentially effective method for planarian studies.

Rapid light-induced activation of retinal microglia in mice lacking Arrestin-1

Microglia dynamically prune synaptic contacts during development, and digest waste that accumulates in degeneration and aging. In many neurodegenerative diseases, microglial activation and phagocytosis gradually increase over months or years, with poorly defined initial triggering events. Here, we describe rapid retinal microglial activation in response to physiological light levels in a mouse model of photoreceptor degeneration that arises from defective rhodopsin deactivation and prolonged signaling. Activation, migration and proliferation of microglia proceeded along a well-defined time course apparent within 12 h of light onset. Retinal imaging in vivo with optical coherence tomography revealed dramatic increases in light-scattering from photoreceptors prior to the outer nuclear layer thinning classically used as a measure of retinal neurodegeneration. This model is valuable for mechanistic studies of microglial activation in a well-defined and optically accessible neural circuit, and for the development of novel methods for detecting early signs of pending neurodegeneration in vivo.

Non-invasive detection of early retinal neuronal degeneration by ultrahigh resolution optical coherence tomography

Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early stages of neuronal degeneration. Using ultrahigh resolution (UHR) OCT imaging at 800 nm (spectral width 140 nm) we developed a robust method of OCT image analyses, based on spatial wavelet and texture-based parameterisation of the image speckle pattern. For the first time we show that this approach allows the non-invasive detection and quantification of early apoptotic changes in neurons within 30 min of neuronal trauma sufficient to result in apoptosis. We show a positive correlation between immunofluorescent labelling of mitochondria (a potential source of changes in cellular optical contrast) with changes in the texture of the OCT images of cultured neurons. Moreover, similar changes in optical contrast were also seen in the retinal ganglion cell- inner plexiform layer in retinal explants following optic nerve transection. The optical clarity of the explants was maintained throughout in the absence of histologically detectable change. Our data suggest that UHR OCT can be used for the non-invasive quantitative assessment of neuronal health, with a particular application to the assessment of early retinal disease.

Evidence of early ultrastructural photoreceptor abnormalities in light-induced retinal degeneration using spectral domain optical coherence tomography

BACKGROUND

To study spatiotemporal in vivo changes in retinal morphology and quantify thickness of retinal layers in a mouse model of light-induced retinal degeneration using spectral domain optical coherence tomography (SD-OCT).

METHODS

BALB/c mice were exposed to 5000 lux of constant light for 3 h. SD-OCT images were taken 3 h, 24 h, 3 days, 1 week and 1 month after light exposure and were compared with histology at the same time points. SD-OCT images were also taken at 0, 1 and 2 h after light exposure in order to analyse retinal changes at the earliest time points. The thickness of retinal layers was measured using the Bioptigen software InVivoVue Diver.

RESULTS

SD-OCT demonstrated progressive outer retinal thinning. 3 h after light exposure, the outer nuclear layer converted from hyporeflective to hyper-reflective. At 24 h, outer retinal bands and nuclear layer demonstrated similar levels of hyper-reflectivity. Significant variations in outer retinal thickness, vitreous opacities and retinal detachments occurred within days of injury. Thinning of the retina was observed at 1 month after injury. It was also determined that outer nuclear layer changes precede photoreceptor segment structure disintegration and the greatest change in segment structure occurs between 1 and 2 h after light exposure.

CONCLUSIONS

Longitudinal SD-OCT reveals intraretinal changes that cannot be observed by histopathology at early time points in the light injury model.

Dose-dependent retinal changes following sodium iodate administration: application of spectral-domain optical coherence tomography for monitoring of retinal injury and endogenous regeneration

BACKGROUND

The purpose of this study was to demonstrate the progression of acute retinal injury by correlating histological sections with in vivo spectral-domain optical coherence tomography (SD-OCT) images.

METHODS

Male C57BL/6 mice were treated intravenously with two different sodium iodate (NaIO3) doses (35 mg/kg or 15 mg/kg). In vivo SD-OCT was performed up to 3 months post-injury. Ex vivo retinal histology, TUNEL and IsolectinB4 immunostaining were also conducted. Quantitative comparison of histopathological images and SD-OCT images was performed.

RESULTS

SD-OCT examination revealed that administration of 35 mg/kg NaIO3 was associated with progressive and irreversible retinal degeneration. On day 3 post-injury, we found numerous apoptotic cells in the outer nuclear layer (ONL) that strongly corresponded to hyper-reflective areas in the SD-OCT images. At 7 d post-injury, SD-OCT images showed irregular-shaped patterns of hyper-reflectivity in the retinal pigment epithelium (RPE) that corresponded with the accumulation of macrophages phagocytosing melanin granules and cell debris. Additionally, we documented hyper-reflective opacities in the vitreous that were most numerous at 7 d. At 3 months post-injury, the neurosensory retina was significantly thinner, predominantly due to progressive photoreceptor (PR) loss. In contrast, administration of 15 mg/kg NaIO3 did not induce hyper-reflectivity of ONL in SD-OCT images, which indicates a lack of massive PR cell death. At 3 months post-injury, SD-OCT images showed the complete restoration of outer retina lamination and restoration of hyper-reflective structural bands. Histological assessment of retinas acquired after the last SD-OCT imaging session revealed complete regeneration of the RPE and considerable improvement of PR architecture.

CONCLUSIONS

Our findings showed the high level of effectiveness of SD-OCT imaging for monitoring dynamic changes in retinal morphology following acute retinal injury. Moreover, we demonstrated for the first time that SD-OCT can be used to non-invasively detect regeneration in the damaged retina.

Depth-resolved model-based reconstruction of attenuation coefficients in optical coherence tomography

We present a method, based on a single scattering model, to calculate the attenuation coefficient of each pixel in optical coherence tomography (OCT) depth profiles. Numerical simulations were used to determine the model's response to different depths and attenuation coefficients. Experiments were performed on uniform and layered phantoms with varying attenuation coefficients. They were measured by a 1300 nm OCT system and their attenuation coefficients were evaluated by our proposed method and by fitting the OCT slope as the gold standard. Both methods showed largely consistent results for the uniform phantoms. On the layered phantom, only our proposed method accurately estimated the attenuation coefficients. For all phantoms, the proposed method largely reduced the variability of the estimated attenuation coefficients. The method was illustrated on an in-vivo retinal OCT scan, effectively removing common imaging artifacts such as shadowing. By providing localized, per-pixel attenuation coefficients, this method enables tissue characterization based on attenuation coefficient estimates from OCT data.

Dual-band Fourier domain optical coherence tomography with depth-related compensations

Dual-band Fourier domain optical coherence tomography (FD-OCT) provides depth-resolved spectroscopic imaging that enhances tissue contrast and reduces image speckle. However, previous dual-band FD-OCT systems could not correctly give the tissue spectroscopic contrast due to depth-related discrepancy in the imaging method and attenuation in biological tissue samples. We designed a new dual-band full-range FD-OCT imaging system and developed an algorithm to compensate depth-related fall-off and light attenuation. In our imaging system, the images from two wavelength bands were intrinsically overlapped and their intensities were balanced. The processing time of dual-band OCT image reconstruction and depth-related compensations were minimized by using multiple threads that execute in parallel. Using the newly developed system, we studied tissue phantoms and human cancer xenografts and muscle tissues dissected from severely compromised immune deficient mice. Improved spectroscopic contrast and sensitivity were achieved, benefiting from the depth-related compensations.

Label-Free, Longitudinal Visualization of PDT Response In Vitro with Optical Coherence Tomography

A major challenge in creating and optimizing therapeutics in the fight against cancer is visualizing and understanding the microscale spatiotemporal treatment response dynamics that occur in patients. This is especially true for photodynamic therapy (PDT), where therapeutic optimization relies on understanding the interplay between factors such as photosensitizer localization and uptake, in addition to light dose and delivery rate. In vitro 3D culture systems that recapitulate many of the biological features of human disease are powerful platforms for carrying out detailed studies on PDT response and resistance. Current techniques for visualizing these models, however, often lack accuracy due to the perturbative nature of the sample preparation, with light attenuation complicating the study of intact models. Optical coherence tomography (OCT) is an ideal method for the long-term, non-perturbative study of in vitro models and their response to PDT. Monitoring the response of 3D models to PDT by time-lapse OCT methods promises to provide new perspectives and open the way to cancer treatment methodologies that can be translated towards the clinic.

Thickness, phase retardation, birefringence, and reflectance of the retinal nerve fiber layer in normal and glaucomatous non-human primates

PURPOSE

We identified candidate optical coherence tomography (OCT) markers for early glaucoma diagnosis. Time variation of retinal nerve fiber layer (RNFL) thickness, phase retardation, birefringence, and reflectance using polarization sensitive optical coherence tomography (PS-OCT) were measured in three non-human primates with induced glaucoma in one eye. We characterized time variation of RNFL thickness, phase retardation, birefringence, and reflectance with elevated intraocular pressure (IOP).

METHODS

One eye of each of three non-human primates was laser treated to increase IOP. Each primate was followed for a 30-week period. PS-OCT measurements were recorded at weekly intervals. Reflectance index (RI) is introduced to characterize RNFL reflectance. Associations between elevated IOP and RNFL thickness, phase retardation, birefringence, and reflectance were characterized in seven regions (entire retina, inner and outer rings, and nasal, temporal, superior and inferior quadrants) by linear and non-linear mixed-effects models.

RESULTS

Elevated IOP was achieved in three non-human primate eyes with an average increase of 13 mm Hg over the study period. Elevated IOP was associated with decreased RNFL thickness in the nasal region (P = 0.0002), decreased RNFL phase retardation in the superior (P = 0.046) and inferior (P = 0.021) regions, decreased RNFL birefringence in the nasal (P = 0.002) and inferior (P = 0.029) regions, and loss of RNFL reflectance in the outer rings (P = 0.018). When averaged over the entire retinal area, only RNFL reflectance showed a significant decrease (P = 0.028).

CONCLUSIONS

Of the measured parameters, decreased RNFL reflectance was the most robust correlate with glaucomatous damage. Candidate cellular mechanisms are considered for decreased RNFL reflectance, including mitochondrial dysfunction and retinal ganglion cell apoptosis.

Quantitative discrimination of NPC cell lines using optical coherence tomography

We tried to explore the intrinsic differences in the optical properties of the four representative NPC cell lines on the models of radiobiology and metastasis by OCT. The scattering coefficients and anisotropies were extracted by fitting the average a-scan attenuation curves based on the multiple scatter effect. The values of scattering coefficients and anisotropy factors were 5.21 ± 0.11, 5.30 ± 0.09, 5.92 ± 0.21, 6.97 ± 0.22, and 0.892 ± 0.009, 0.886 ± 0.006, 0.884 ± 0.009, 0.86 ± 0.01 for CNE1, CNE2, 5-8F and 6-10B pellets (p < 0.05, P = 0.07 for CNE1 and CNE2), respectively. The results showed that the radiobiology and metastasis cell's model could be distinguished obviously; which implied that the corresponding types of NPC tissue might be potentially differentiated by OCT.

Quantitative measurement of optical parameters of cell lines 5-8F and 6-10B using polarization sensitive optical coherence tomography

The aim was to test whether the typical NPC cell lines of 5-8F (high tumorigenesis and metastasis) and 6-10B (low tumorigenesis and metastasis) could be differentiated by polarization sensitive optical coherence tomography (PS-OCT). We imaged the two types of low cellular differentiated NPC cell lines 5-8F and 6-10B pellets using PS-OCT; then extracted the optical parameters of attenuate coefficient and anisotropy from the A-scan lines based on the multiple scattering model; and compared their phase retardation. The fitting scattering coefficients were μs=10.91±0.45 and μs=11.33±0.27 cm(-1) for 5-8F and 6-10B pellets (p<0.05), respectively; and the anisotropy factors were g=0.900±0.013 and g=0.885±0.008 for 5-8F and 6-10B pellets (p<0.01), respectively. While the phase retardation of 6-10B was a little faster than 5-8F. These results indicated that PS-OCT could differentiate the two cell lines, and had the potential ability for typing the tissue of NPC.

Quantitative measurement of optical attenuation coefficients of cell lines CNE1, CNE2, and NP69 using optical coherence tomography

The radiotherapy-related types of nasopharyngeal carcinoma (NPC) have been established, which give the most effective treatment for NPC patients using the individual therapy. To diagnose the types of NPC, we assess the general NPC cell lines CNE1, CNE2 and normal nasopharyngeal cell line NP69 using optical coherence tomography (OCT) in two steps: firstly, the OCT images of the three different types of cell pellets are captured. Secondly, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (μ t ) of the cells can be extracted. The median attenuation coefficients (interquartile range) of CNE1, CNE2, and NP69 are 5.58 mm(-1) (IQR 5.55 to 5.65 mm(-1)), 5.91 mm(-1) (IQR 5.82 to 5.88 mm(-1)), and 8.96 mm(-1) (IQR 8.80 to 9.47 mm(-1)), respectively. The distinguishable quantitative OCT analysis (by μ t ) shows that the types of NPC could potentially be differentiated in real time and noninvasive.

Parametric imaging of the local attenuation coefficient in human axillary lymph nodes assessed using optical coherence tomography

We report the use of optical coherence tomography (OCT) to determine spatially localized optical attenuation coefficients of human axillary lymph nodes and their use to generate parametric images of lymphoid tissue. 3D-OCT images were obtained from excised lymph nodes and optical attenuation coefficients were extracted assuming a single scattering model of OCT. We present the measured attenuation coefficients for several tissue regions in benign and reactive lymph nodes, as identified by histopathology. We show parametric images of the measured attenuation coefficients as well as segmented images of tissue type based on thresholding of the attenuation coefficient values. Comparison to histology demonstrates the enhancement of contrast in parametric images relative to OCT images. This enhancement is a step towards the use of OCT for in situ assessment of lymph nodes.

Single cell viability measurements in 3D scaffolds using in situ label free imaging by optical coherence microscopy

The focus on creating tissue engineered constructs of clinically relevant sizes requires new approaches for monitoring construct health during tissue development. A few key requirements are that the technology be in situ, non-invasive, and provide temporal and spatial information. In this work, we demonstrate that optical coherence microscopy (OCM) can be used to assess cell viability without the addition of exogenous probes in three-dimensional (3D) tissue scaffolds maintained under standard culture conditions. This is done by collecting time-lapse images of speckle generated by sub-cellular features. Image cross-correlation is used to calculate the number of features the final image has in common with the initial image. If the cells are live, the number of common features is low. The number of common features approaches 100% if the cells are dead. In control experiments, cell viability is verified by the addition of a two-photon fluorescence channel to the OCM. Green fluorescent protein transfected human bone marrow stromal cells cultured in a transparent poly(ethylene glycol) tetramethacrylate hydrogel scaffold is used as the control system. Then, the utility of this approach is demonstrated by determining L929 fibroblast cell viability in a more challenging matrix, collagen, an optical scatterer. These results demonstrate a new technique for in situ mapping of single cell viability without any exogenous probes that is capable of providing continuous monitoring of construct health.

Detecting cell death with optical coherence tomography and envelope statistics

Currently no standard clinical or preclinical noninvasive method exists to monitor cell death based on morphological changes at the cellular level. In our past work we have demonstrated that quantitative high frequency ultrasound imaging can detect cell death in vitro and in vivo. In this study we apply quantitative methods previously used with high frequency ultrasound to optical coherence tomography (OCT) to detect cell death. The ultimate goal of this work is to use these methods for optically-based clinical and preclinical cancer treatment monitoring. Optical coherence tomography data were acquired from acute myeloid leukemia cells undergoing three modes of cell death. Significant increases in integrated backscatter were observed for cells undergoing apoptosis and mitotic arrest, while necrotic cells induced a decrease. These changes appear to be linked to structural changes observed in histology obtained from the cell samples. Signal envelope statistics were analyzed from fittings of the generalized gamma distribution to histograms of envelope intensities. The parameters from this distribution demonstrated sensitivities to morphological changes in the cell samples. These results indicate that OCT integrated backscatter and first order envelope statistics can be used to detect and potentially differentiate between modes of cell death in vitro.