One‐to‐one registration of en‐face optical coherence tomography attenuation coefficients with histology of a prostatectomy specimen

Optical coherence tomography (OCT), enables high‐resolution 3D imaging of the morphology of light scattering tissues. From the OCT signal, parameters can be extracted and related to tissue structures. One of the quantitative parameters is the attenuation coefficient; the rate at which the intensity of detected light decays in depth. To couple the quantitative parameters with the histology one‐to‐one registration is needed. The primary aim of this study is to validate a registration method of quantitative OCT parameters to histological tissue outcome through one‐to‐one registration of OCT with histology. We matched OCT images of unstained fixated prostate tissue slices with corresponding histology slides, wherein different histologic types were demarcated. Attenuation coefficients were determined by a supervised automated exponential fit (corrected for point spread function and sensitivity roll‐off related signal losses) over a depth of 0.32 mm starting from 0.10 mm below the automatically detected tissue edge. Finally, the attenuation coefficients corresponding to the different tissue types of the prostate were compared. From the attenuation coefficients, we produced the squared relative residue and goodness‐of‐fit metric R². This article explains the method to perform supervised automated quantitative analysis of OCT data, and the one‐to‐one registration of OCT extracted quantitative data with histopathological outcomes.      

Multicontrast endomyocardial imaging by single‐channel high‐resolution cross‐polarization optical coherence tomography

A single‐channel high‐resolution cross‐polarization (CP) optical coherence tomography (OCT) system is presented for multicontrast imaging of human myocardium in one‐shot measurement. The intensity and functional contrasts, including the ratio between the cross‐ and co‐polarization channels as well as the cumulative retardation, are reconstructed from the CP‐OCT readout. By comparing the CP‐OCT results with histological analysis, it is shown that the system can successfully delineate microstructures in the myocardium and differentiate the fibrotic myocardium from normal or ablated myocardium based on the functional contrasts provided by the CP‐OCT system. The feasibility of using A‐line profiles from the 2 orthogonal polarization channels to identify fibrotic myocardium, normal myocardium and ablated lesion is also discussed.      

Optical coherence tomography follow‐up of patients treated from periodontal disease

Optical coherence tomography (OCT) is one of the most important imaging modalities for biophotonics applications. In this work, an important step towards the clinical use of OCT in dental practice is reported, by following‐up patients treated from periodontal disease (PD). A total of 147 vestibular dental sites from 14 patients diagnosed with PD were evaluated prior and after treatment, using a swept‐source OCT and two periodontal probes (Florida probe and North Carolina) for comparison. The evaluation was performed at four stages: day 0, day 30, day 60 and day 90. Exceptionally one patient was evaluated 1‐year after treatment. It was possible to visualize in the two‐dimensional images the architectural components that compose the periodontal anatomy, and identify the improvements in biofilm and dental calculus upon treatment. In the follow‐up after the treatment, it was observed in some cases decrease of the gingival thickness associated with extinction of gingival calculus. In some cases, the improvement of both depth of probing with the traditional probes and the evidence in the images of the region was emphasized. The study evidenced the ability of OCT in the identification of periodontal structures and alterations, being an important noninvasive complement or even alternative for periodontal probes for treatment follow‐up. OCT system being used in a clinical environment. Above OCT image (left) prior treatment and (right) 30 days after treatment.      

Depth‐resolved multimodal imaging: Wavelength modulated spatially offset Raman spectroscopy with optical coherence tomography

A major challenge in biophotonics is multimodal imaging to obtain both morphological and molecular information at depth. We demonstrate a hybrid approach integrating optical coherence tomography (OCT) with wavelength modulated spatially offset Raman spectroscopy (WM‐SORS). With depth colocalization obtained from the OCT, we can penetrate 1.2‐mm deep into strong scattering media (lard) to acquire up to a 14‐fold enhancement of a Raman signal from a hidden target (polystyrene) with a spatial offset. Our approach is capable of detecting both Raman and OCT signals for pharmaceutical particles embedded in turbid media and revealing the white matter at depth within a 0.6‐mm thick brain tissue layer. This depth resolved label‐free multimodal approach is a powerful route to analyze complex biomedical samples.      

Three‐dimensional static optical coherence elastography based on inverse compositional Gauss‐Newton digital volume correlation

The three‐dimensional (3D) mechanical properties characterization of tissue is essential for physiological and pathological studies, as biological tissue is mostly heterogeneous and anisotropic. A digital volume correlation (DVC)‐based 3D optical coherence elastography (OCE) method is developed to measure the 3D displacement and strain tensors. The DVC algorithm includes a zero‐mean normalized cross‐correlation criterion‐based coarse search regime, an inverse compositional Gauss‐Newton fine search algorithm and a local ternary quadratic polynomial fitting strain calculation method. A 3D optical coherence tomography (OCT) scanning protocol is proposed through theoretical analysis and experimental verification. Measurement errors of the DVC‐based 3D OCE method are evaluated to be less than 2.0 μm for displacements and 0.30% for strains by rigid body motion experiments. The 3D displacements and strains of a phantom and a specimen of chicken breast tissue under compression are measured. Results of the phantom show a good agreement with theoretical analysis and tensile testing. The strains of the chicken breast tissue indicate anisotropic biomechanical properties. This study provides an effective method for 3D biomechanical property studies of soft tissue and improves the development of 3D OCE techniques.     

High‐definition optical coherence tomography of melanocytic skin lesions

High‐definition optical coherence tomography (HD‐OCT) scanners have recently been developed. We assessed micromorphological HD‐OCT correlates of benign naevi (BN) and malignant melanoma (MM). 28 BN and 20 MM were studied using HD‐OCT and histology. Epidermal honeycomb/cobblestone pattern, regular junctional cell nests, and edged papillae are more often observed in BN, whereas fusion of rete ridges, pagetoid cells and junctional and/or dermal nests with atypical cells are more frequently seen in MM. A high overlap of HD‐OCT features in BN and MM was observed and in 20% of MM we did not find evidence for malignancy in OCT images at all. Using HD‐OCT it is possible to visualize architectural and cellular alterations of melanocytic skin lesions. The overlap of HD‐OCT features seen in BN and MM and the absence of suspicious HD‐OCT features in some MM represents an important limitation of HD‐OCT affecting the sensitivity of HD‐OCT in diagnosing MM.

High‐definition optical coherence tomography and the corresponding vertically sectioned histology of a compound naevus.     

Automated three‐dimensional cell counting method for grading uveitis of rodent eye in vivo with optical coherence tomography

In preclinical vision research, cell grading in small animal models is essential for the quantitative evaluation of intraocular inflammation. Here, we present a new and practical optical coherence tomography (OCT) image analysis method for the automated detection and counting of aqueous cells in the anterior chamber (AC) of a rodent model of uveitis. Anterior segment OCT images are acquired with a 100 kHz swept‐source OCT system. The proposed method consists of 2 steps. In the first step, we first despeckle and binarize each OCT image. After removing AS structures in the binary image, we then apply area thresholding to isolate cell‐like objects. Potential cell candidates are selected based on their best fit to roundness. The second step performs the cell counting within the whole AC, in which additional cell tracking analysis is conducted on the successive OCT images to eliminate redundancy in cell counting. Finally, 3D cell grading using the proposed method is demonstrated in longitudinal OCT imaging of a mouse model of anterior uveitis in vivo. Rendering of anterior segment (orange) of mouse eye and automatically counted anterior chamber cells (green). Inset is a top view of the rendering, showing the cell distribution across the anterior chamber.      

Quantitative and rapid estimations of human sub‐surface skin mass using ultra‐high‐resolution spectral domain optical coherence tomography

Non‐invasive and quantitative estimations for the delineation of sub‐surface tumor margins could greatly aid in the early detection and monitoring of the morphological appearances of tumor growth, ensure complete tumor excision without the unnecessary sacrifice of healthy tissue, and facilitate post‐operative follow‐up for recurrence. In this study, a high‐speed, non‐invasive, and ultra‐high‐resolution spectral domain optical coherence tomography (UHR‐SDOCT) imaging platform was developed for the quantitative measurement of human sub‐surface skin mass. With a proposed robust, semi‐automatic analysis, the system can rapidly quantify lesion area and shape regularity by an en‐face‐oriented algorithm. Various sizes of nylon sutures embedded in pork skin were used first as a phantom to verify the accuracy of our algorithm, and then in vivo, feasibility was proven using benign human angiomas and pigmented nevi. Clinically, this is the first step towards an automated skin lesion measurement system.

In vivo optical coherence tomography (OCT) image of angioma (A). Thin red arrows point to a blood vessel (BV).     

Super‐achromatic optical coherence tomography capsule for ultrahigh‐resolution imaging of esophagus

Endoscopic optical coherence tomography (OCT) is a noninvasive technology allowing for imaging of tissue microanatomies of luminal organs in real time. Conventional endoscopic OCT operates at 1300 nm wavelength region with a suboptimal axial resolution limited to 8‐20 μm. In this paper, we present the first ultrahigh‐resolution tethered OCT capsule operating at 800 nm and offering about 3‐ to 4‐fold improvement of axial resolution (plus enhanced imaging contrast). The capsule uses diffractive optics to manage chromatic aberration over a full ~200 nm spectral bandwidth centering around 830 nm, enabling to achieve super‐achromaticity and an axial resolution of ~2.6 μm in air. The performance of the OCT capsule is demonstrated by volumetric imaging of swine esophagus ex vivo and sheep esophagus in vivo, where fine anatomic structures including the sub‐epithelial layers are clearly identified. The ultrahigh resolution and excellent imaging contrast at 800 nm of the tethered capsule suggest the potential of the technology as an enabling tool for surveillance of early esophageal diseases on awake patients without the need for sedation.      

General model for depth‐resolved estimation of the optical attenuation coefficients in optical coherence tomography

We present the proof of concept of a general model that uses the tissue sample transmittance as input to estimate the depth‐resolved attenuation coefficient of tissue samples using optical coherence tomography (OCT). This method allows us to obtain an image of tissue optical properties instead of intensity contrast, guiding diagnosis and tissues differentiation, extending its application from thick to thin samples. The performance of our method was simulated and tested with the assistance of a home built single‐layered and multilayered phantoms (~100 μm each layer) with known attenuation coefficient on the range of 0.9 to 2.32 mm^?1. It is shown that the estimated depth‐resolved attenuation coefficient recovers the reference values, measured by using an integrating sphere followed by the inverse adding doubling processing technique. That was corroborated for all situations when the correct transmittance value is used with an average difference of 7%. Finally, we applied the proposed method to estimate the depth‐resolved attenuation coefficient for a thin biological sample, demonstrating the ability of our method on real OCT images.     

Intravascular magnetomotive optical coherence tomography of targeted early‐stage atherosclerotic changes in ex vivo hyperlipidemic rabbit aortas

We report the development of an intravascular magnetomotive optical coherence tomography (IV‐MM‐OCT) system used with targeted protein microspheres to detect early‐stage atherosclerotic fatty streaks/plaques. Magnetic microspheres (MSs) were injected in vivo in rabbits, and after 30 minutes of in vivo circulation, excised ex vivo rabbit aorta samples specimens were then imaged ex vivo with our prototype IV‐MM‐OCT system. The alternating magnetic field gradient was provided by a unique pair of external custom‐built electromagnetic coils that modulated the targeted magnetic MSs. The results showed a statistically significant MM‐OCT signal from the aorta samples specimens injected with targeted MSs.

Representative magnetomotive signal (green) using targeted and non‐targeted magnetomotive microspheres in atherosclerotic diseased rabbit aortas.     

Pixel classification method in optical coherence tomography for tumor segmentation and its complementary usage with OCT microangiography

A novel machine‐learning method to distinguish between tumor and normal tissue in optical coherence tomography (OCT) has been developed. Pre‐clinical murine ear model implanted with mouse colon carcinoma CT‐26 was used. Structural‐image‐based feature sets were defined for each pixel and machine learning classifiers were trained using “ground truth” OCT images manually segmented by comparison with histology. The accuracy of the OCT tumor segmentation method was then quantified by comparing with fluorescence imaging of tumors expressing genetically encoded fluorescent protein KillerRed that clearly delineates tumor borders. Because the resultant 3D tumor/normal structural maps are inherently co‐registered with OCT derived maps of tissue microvasculature, the latter can be color coded as belonging to either tumor or normal tissue. Applications to radiomics‐based multimodal OCT analysis are envisioned.      

The use of intensity‐based Doppler variance method for single vessel response to functional neurovascular activation

This study presents 1 use of optical coherence tomography (OCT) angiography technique to examine neurovascular coupling effect. Repeated B‐scans OCT recording is performed on the rat somatosensory cortex with cranial window preparation while its contralateral forepaw is electrically stimulated to activate the neurons in rest. We use an intensity‐based Doppler variance (IBDV) algorithm mapped cerebral blood vessels in the cortex, and the temporal alteration in blood perfusion during neurovascular activation is analyzed using the proposed IBDV quantitative parameters. By using principal component analysis‐based Fuzzy C Means clustering method, the stimulus‐evoked vasomotion patterns were classified into 3 categories. We found that the response time of small vessels (resting diameter 14.9 ±6.6 μm), middle vessels (resting diameter 21.1 ±7.9 μm) and large vessels (resting diameter 50.7 ±6.5 μm) to achieve 5% change of vascular dilation after stimulation was 1.5, 2 and 5.5 seconds, respectively. Approximately 5% peak change of relative blood flow (RBF) in both small and middle vessels was observed. The large vessels react slowly and their responses nearly 4 seconds delayed, but no significant change in RBF of the large vessels was seen.      

Spectrally encoded coherence tomography and reflectometry: Simultaneous en face and cross‐sectional imaging at 2 gigapixels per second

Non‐invasive biological imaging is crucial for understanding in vivo structure and function. Optical coherence tomography (OCT) and reflectance confocal microscopy are two of the most widely used optical modalities for exogenous contrast‐free, high‐resolution, three‐dimensional imaging in non‐fluorescent scattering tissues. However, sample motion remains a critical barrier to raster‐scanned acquisition and reconstruction of wide‐field anatomically accurate volumetric datasets. We introduce spectrally encoded coherence tomography and reflectometry (SECTR), a high‐speed, multimodality system for simultaneous OCT and spectrally encoded reflectance (SER) imaging. SECTR utilizes a robust system design consisting of shared optical relays, scanning mirrors, swept laser and digitizer to achieve the fastest reported in vivo multimodal imaging rate of 2 gigapixels per second. Our optical design and acquisition scheme enable spatiotemporally co‐registered acquisition of OCT cross‐sections simultaneously with en face SER images for multivolumetric mosaicking. Complementary axial and lateral translation and rotation are extracted from OCT and SER data, respectively, for full volumetric estimation of sample motion with micron spatial and millisecond temporal resolution.      

Retinal imaging with optical coherence tomography and low‐loss adaptive optics using a 2.8‐mm beam size

As data acquisition for retinal imaging with optical coherence tomography (OCT) becomes faster, efficient collection of photons becomes more important to maintain image quality. One approach is to use a larger aperture at the eye's pupil to collect more photons that have been reflected from the retina. A 2.8‐mm beam diameter system with only seven reflecting surfaces was developed for low‐loss retinal imaging. The larger beam size requires defocus and astigmatism correction, which was done in a closed loop adaptive optics method using a Shack‐Hartmann wavefront sensor and a deformable mirror (DM) with 140 actuators and a ±2.75 μm stroke. This DM facilitates defocus correction ranging from approximately ?3 D to +3 D. Comparing the new system with a standard 1.2‐mm system on a model eye, a signal‐to‐noise gain of 4.5 dB and a 2.3 times smaller speckle size were measured. Measurements on the retinas of five subjects showed even better results, with increases in dynamic range up to 13 dB. Note that the new sample arm only occupies 30 cm × 60 cm, which makes it highly suitable for imaging in a clinical environment. Figure: B‐scan images obtained over a width of 8 deg from the right eye of a 31‐year‐old Caucasian male. While the left side was imaged with a standard 1.2‐mm OCT system, the right side was imaged with the 2.8‐mm system. Both images were collected with the same integration time and incident power, after correction of aberrations. Using the dynamic range within the images, which is determined by comparing the highest pixel value to the noise floor, a difference in dynamic range of 10.8 dB was measured between the two systems.      

On the role of interference in laser‐based mid‐infrared widefield microspectroscopy

A laser's high degree of coherence leads to interferences, which—in the absence of precautions—can cause severe image distortions such as fringes and speckles and which thereby strongly hamper a meaningful interpretation of hyperspectral images in laser‐based widefield microspectroscopy. While images and spectra of homogenous samples may already suffer from interferences, any structured object such as a tissue thin section will add to these distortions due to wavelength‐ and, in particular, sample‐dependent phase shifts (structure sizes, absorption coefficients, refractive indices). This effect is devastating for the universal applicability of laser‐based microspectroscopy especially in the mid‐infrared (MIR), where cell sizes are of the same dimension as the wavelength of the illumination source. Here, we show that the impact of interferences is strongly mitigated by reducing the time‐averaged spatiotemporal coherence properties of the illumination using a moving plus a stationary scatterer. In this case, the illumination path provides a pseudothermal radiation source and spatially resolved spectra can be obtained at the quality of the reference method, that is, Fourier‐transform infrared microspectroscopy, without compromising spectral or spatial resolution.      

Real‐time in vivo imaging of adult Zebrafish brain using optical coherence tomography

We report noninvasive imaging of the brain of adult Zebrafish (Danio rerio) using real time optical coherence tomography (OCT) capable of acquiring cross sectional 2D OCT images @ 8 frames/sec. Anatomic features such as telencephalon, tectum opticum, eminentia Granularis and cerebellum were clearly resolved in the OCT images. A 3D model of Zebrafish brain was reconstructed, for the first time to our knowledge, using these 2D OCT images. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In vivo visualization of<Emphasis Type="Italic"> Tradescantia</Emphasis> leaf tissue and monitoring the physiological and morphological states under different water supply conditions using optical coherence tomography

The optical coherence tomography (OCT) capabilities of plants were evaluated using leaves of Tradescantia pallida (Rose) D. Hunt. The internal structure of the leaf tissues was visualized in vivo and the physiological and morphological states of the tissues under different water supply conditions were monitored using OCT. The OCT technique provides non-invasive two-dimensional images directly on intact plants. The acquisition time of a two-dimensional image with a size of 200×200 pixels and a spatial resolution of 15 m is 1–3 s. It was shown that OCT is a useful tool for monitoring the physiological and morphological states of plant tissues supplied with varying amounts of water and under the influence of different chemical factors.Abbreviation OCT Optical coherence tomography     

Clinical assessment of non carious cervical lesion using swept‐source optical coherence tomography

Non‐carious cervical lesions (NCCLs) involve various forms of tooth loss with different etiologies. This study aimed to utilize swept‐source optical coherence tomography (SS‐OCT) at 1300 nm wavelength range in vitro and in vivo to evaluate and clarify the mechanism of NCCLs. In the in vitro phase, a dentin attenuation coefficient (μ_t) derived from the SS‐OCT signal at NCCL was compared with mineral loss obtained from transverse microradiography (TMR) to determine a μ_t threshold to discriminate demineralization of cervical dentin in vivo. In the clinical study, 242 buccal surfaces were investigated in 35 subjects. Presence and dimensions of NCCLs, cervical cracking and the degree of demineralization at the exposed cervical dentin were determined using SS‐OCT. Dentin demineralization was observed in 69% of NCCLs. SS‐OCT results confirm that dentin mineral loss and occlusal attrition were associated with larger NCCLs, and can be considered as an etiological factor in formation and progress of these lesions.

( A ) We determined the attenuation coeffcient (μ_t) threshold of SS‐OCT signal for the detection of demineralization (1.21) from in vitro study. DEM: demineralized dentin, sound: sound dentin. ( B ) Using the μ_t threshold, we observed NCCLs in vivo to detect the demineralization in cervical dentin. SS‐OCT scanning was performed along the red line. ( C ) SS‐OCT image obtained along the red line in B. In SS‐OCT, brightness of dentin beneath the NCCL was increased (arrow) compared with intact zone. The cervical dentin was slightly demineralized (μ_t: 1.25). e: enamel, d: dentin, g: gingiva.