Optical coherence tomography using a frequency-tunable optical source

Optical frequency domain reflectometry (OFDR) measurements are performed by recording the interference pattern of light backscattered by density fluctuations or Bragg gratings along the length of an optical fiber. Changes in local temperature or strain in the fiber cause shifts in the backscattered light spectrum, which can be calibrated to the applied temperature or strain. Comparing the backscattered optical spectra from each reflection site with a reference (unstrained) spectrum allows for quantification of local spectral shifts. While mature OFDR-based technologies can provide high-precision spatially distributed measurements over kilometer lengths, the post-processing approaches used to recover spectral shifts from raw optical intensity data can limit the use of OFDR in harsh environments. This paper presents a novel approach to post-processing OFDR data which extends the usability of optical fibers exposed to harsh environments. This approach is the first to use the spectral shift quality, calculated for two OFDR measurements, to identify an appropriate reference scan from which the spectral shift can be determined. Three experimental data sets are used to test the algorithm: (1) an optical fiber heated to >950°C, (2) an aluminum-embedded optical fiber under strain from differential thermal expansion, and (3) an optical fiber exposed to a total neutron flux of $2\times 10^{13}$ n/cm2/s over 40 hours in a nuclear test reactor. Results show that using a metric of quality to select an appropriate reference measurement extends the functional range of OFDR strain and temperature sensors. Furthermore, this algorithm can be applied to existing OFDR data.

As the security of optical fiber lines in data centers has attracted growing attention, it has become increasingly important to accurately characterize the fiber that is used. Optical frequency domain reflectometry (OFDR) has been demonstrated as a means of identifying specific segments of optical fiber; however, OFDR measurements are limited in length due to initial optical frequency (IOF) variations. This Letter describes a detailed analysis of IOF and introduces a method to mitigate it in an OFDR system constructed using a semiconductor laser (SCL). Additionally, an algorithm is described that minimizes the calculating density necessary for OFDR-based optical fiber verification, reducing the calculating time required by an order of magnitude relative to prior techniques. Experiments demonstrate that the described method can be effectively applied to a range of application areas, ranging from centimeter to meter lengths of optical fiber, with an error equal rate (EER) of less than 1%.

Optical coherence tomography (OCT) technology can generate cross-sectional images of the scattering media such as biological tissues with spatial resolution as low as 1 ~ 10 mum. OCT uses a partial coherence Michelson interferometry that produces images similar to the ultrasound B-scans. There are many types of functional OCT technologies including polarization-sensitive OCT (PS-OCT), spectroscopic OCT, Optical Doppler Tomography (ODT), etc.PS-OCT produces not only the structural cross-sectional images but the functional images related to the tissue birefringence, phase retardation and depolarization of light reflected from deep tissue regions. Because the PS-OCT is sensitive to birefringent materials such as collagen, the PS-OCT has been studied as an optical diagnosis tool in skin, bone, cartilage, and tooth. In dermatology, OCT can generate useful images such as skin topology and basement membranes. It also can produce other useful images related to skin collagen morphologies and photoaging. We have also demonstrated that the PS-OCT can be applied to clinical problems such as wound healing monitoring of skin. Light depolarization due to multiple scattering is often considered as a negative effect during OCT image acquisition which prevents imaging of deep regions. In our study, we show that the scattering changes can be quantified using PS-OCT by measuring the axial variations of degree of polarization (DOP). Therefore, we suggest that the depolarization process can be used in a positive way. We have tested our hypothesis using various optical phantoms. Scattering changes often occur in pathologic conditions of human cervical tissues. We successfully applied our technique to in vitro diagnosis of cervical interepithelial neoplasm (CIN). It was found that the high-grade squamous intraepithelial lesions (H-SIL) including CIN-II, CIN-III, and Carcinoma in situ (CIS) can be diagnosed by DOP quantification with high sensitivity and specificity.

To evaluate the feasibility of detecting macrophage content on atherosclerotic plaques by optical coherence tomography (OCT) technique. Thirty New Zealand white rabbits were equally divided into 3 groups at random: Control group (fed normal rabbit chow, n = 10); lipid diet group (fed regular chow supplemented with cholesterol, n = 10) and balloon injury+ lipid diet group (balloon catheter injury of the common carotid artery after 2 weeks lipid diet, n = 10). After 12 weeks, all rabbits underwent pharmacological triggering with Chinese Russell's viper venom (CRVV, 15 mg/kg, i.p.) and histamine (0.02 mg/kg, i.v.). Common carotid arteries were detected with OCT and the Movat pentachrome stain respectively. OCT and histological examination results were compared and the correlation was analyzed. The intra thickness measured by Movat pentachrome stain and by the OCT was (15.2 ± 0.9) µm and (20.2 ± 7.6) µm, the medial thickness was (434.2 ± 86.5) µm and (453.8 ± 87.2) µm, the plaque thickness was (330.2 ± 87.1) µm and (392.2 ± 134.5) µm, the fibrous cap thickness was (58.3 ± 5.6) µm and (61.2 ± 4.9) µm, respectively (all P > 0.05). The normalized standard deviation of the OCT signal (NSD) was compared with immunohistochemical detection. The OCT signal within the cap is relatively homogeneous for low macrophage density in high lipid diet group. For the raw OCT data, a correlation of r = 0.846 (P < 0.01) was found between OCT NSD and a CD68 area<10%, whereas for the base 10 logarithm OCT data, a correlation of r = 0.646 (P < 0.05) was found between OCT NSD and a CD68 area<10%. In balloon injury + high lipid diet group, the OCT signal within the cap was relatively heterogeneous for high macrophage content. For the raw OCT data, a correlation of r = 0.906 (P < 0.01) was found between OCT NSD and a CD68 area >10%, whereas for the base 10 logarithm OCT data, a correlation of r = 0.593 (P < 0.05) was found between OCT NSD and a CD68 area >10%. For the raw OCT signal NSD, a range of NSDs (7.12% to 7.35%) demonstrated 100% sensitivity and specificity (Kappa value 1.0) for differentiating caps containing >10% CD68 staining. For the base 10 logarithm OCT signal, NSD values ranging from 7.81% to 7.92% provided 70% sensitivity and 75% specificity (value 0.44) for identifying caps containing >10% CD68 staining. OCT is an effective tool to determine macrophage content in this model. OCT imaging can clearly visualize different types of atherosclerotic plaques and provide detailed information on plaque characteristics.

Optical coherence tomography (OCT) is a noninvasive imaging modality generating cross sectional and volumetric images of translucent samples. In Fourier domain OCT (FD OCT), the depth profile is calculated by a fast Fourier transformation of the interference spectrum, providing speed and SNR advantage and thus making FD OCT well suitable in biomedical applications. The interference spectrum can be acquired spectrally resolved in spectral domain OCT or time-resolved in optical frequency domain imaging (OFDI). Since OCT images still suffer from motion artifacts, especially under in vivo conditions, increased depth scan rates are required. Therefor, the principle of Fourier domain mode locking has been presented by R. Huber et al. circumventing the speed limitations of conventional FD OCT systems. In FDML lasers, a long single mode fiber is inserted in the ring resonator of the laser resulting in an optical round trip time of a few microseconds. Sweeping the wavelength synchronously by a tunable Fabry-Perot filter can provide wavelength sweeps with repetition rates up to a few MHz used for OFDI. Imaging of subpleural lung tissue for investigation of lung dynamics and its elastic properties is a further biomedical application demanding high-speed OCT imaging techniques. For the first time, the visualization of subpleural alveolar structures of a rabbit lung is presented by the use of an FDML-based OCT system enabling repetition rates of 49.5 kHz and 122.6 kHz, respectively.

Purpose To compare Retinal Nerve Fiber Layer measurements with Time Domain Optical Coherence Tomograph (OCT) and Spectral Domain OCT and to get a formula to extrapole thickness results from time domain to spectral domain OCT. Methods Thirty patients with Type 1 diabetes (DM) without retinopathy were prospective and consecutively studied. All underwent imaging of Retinal Nerve Fiber Layer with Stratus OCT (Carl Zeiss Meditec, Inc.)(Fast RNFL thickness scan strategy), Cirrus HD OCT (Carl Zeiss Meditec, Inc.)(optic disc scan stratagy) and Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany)(RNFL scan strategy). RNFL measurements with the 3 devices were compared for the average thickness and for the four quadrants. Results Mean RNFL average thickness was 100.02 ± 11.28 microns with Stratus OCT, 95.35 ± 8.38 μm with Cirrus OCT and 98.9 ± 8.92 μm using Spectralis OCT. All RNFL measurements show significant differences except nasal quadrant between cirrus and stratus, and temporal quadrant between stratus and spectralis. We found that Stratus average thickness is 4.67 microns larger than Cirrus, and 1.12 microns higher than Spectralis OCT. Conclusion Retinal Nerve Fiber Layer measurements show differences between Stratus, Cirrus and Spectralis OCT in type 1 DM patients without retinopathy.The 3 device are not directly comparable.

To investigate morphological variations in the macular area with optical coherence tomography (OCT) after vitrectomy for diabetic fibrovascular proliferation. We reviewed 108 cases using OCT 7-15 months after vitrectomy. Of these, 32 received OCT within 3 months postoperatively. Morphological variations were categorized and correlated with visual outcome. Only 24 cases (21.4%) had no obvious abnormalities. The most frequent findings were epiretinal membrane (52.8%), macular thickening (37.0%) and macular cysts (28.7%). Multivariate regression showed that diffuse macular thickening, loss of foveal depression and diffuse retinal thinning were significantly associated with poor visual acuity. Sequential OCT (< 3 and >or= 7 months) revealed that epiretinal membrane and oedema outside of fovea changed significantly between two examinations. OCT may identify diverse morphological changes in the macular area after diabetic vitrectomy for fibrovascular proliferation. Macular appearance may change over time, and certain types of morphological changes may be associated with poor visual function.

Objective To investigate the imaging features of optical coherence tomography (OCT) in diabetic retinopathy (DR). Methods From January 2015 to December 2017, 104 cases (208 eyes) with DR in the Ophthalmology Department of Inner Mongolia Hospital of Traditional Chinese Medicine were collected, and 289 cases (578 eyes) with DR in Tongren Ophthalmology Center of Beijing Tongren Hospital affiliated to Capital Medical University were collected. A total of 393 cases (786 eyes) were included in the two sites. Among them, there were 181 cases (356 eyes) and 212 cases (430 eyes). The age was 22~88 years, with an average age of (47.30 + 5.42) years. Name, sex, age, address, diabetes history, clinical diagnosis, fundus color photography and OCT report were recorded. Summarize and extract features in each phase of OCT inspection. Results According to the clinical staging standard of DR in 2002, 393 cases (786 eyes) were divided into three groups: 51 cases (102 eyes), 83 cases (166 eyes), 124 cases (248 eyes), 46 cases (92 eyes), 57 cases (114 eyes) and 32 cases (64 eyes) of DR stage VI. Eye only. The OCT of DR stage I was characterized by microangioma, occasional or minor bleeding spots between the retinal neuroepithelial layers; the OCT of DR stage II was characterized by rigid exudation and bleeding spots between the retinal neuroepithelial layers; the OCT of DR stage III was characterized by cotton flocculent plaques in addition to hard exudation and bleeding spots; and the OCT of DR stage IV was characterized by cotton flocculent plaques. In addition to hard exudation, bleeding spots and cotton wadding spots, there are also edema or cystoid edema and/or vitreous hemorrhage; in DRV stage, the OCT features are not only hard exudation, bleeding spots, cotton wadding spots, edema and vitreous hemorrhage, but also organic film; in DRVI stage, the OCT features are hard exudation, bleeding spots and vitreous hemorrhage. There were also traction retinal detachment outside cotton spots, edema, vitreous hemorrhage and organic membrane. In addition, according to the different stages of DR, blood flow OCT imaging (OCTA) can clearly show the characteristics of microangioma, hard exudation, hemorrhage, cystic edema, no perfusion area and neovascularization. Conclusion In the examination results of OCT, DR can appear characteristic image according to different stages. Mastering and using OCT can determine the clinical stages of DR and guide the clinical diagnosis and treatment. Key words: Diabetic retinopathy; Clinical stages; Diagnose; Optical coherence tomography

The murine model is a common model for studying developmental diseases. In this study, we compare the performance of the relatively new method of Optical Projection Tomography (OPT) to the well-established technique of Optical Coherence Tomography (OCT) to assess murine embryonic development at three stages, 9.5, 11.5, and 13.5 days post conception. While both methods can provide spatial resolution at the micrometer scale, OPT can provide superior imaging depth compared to OCT. However, OPT requires samples to be fixed, placed in an immobilization media such as agar, and cleared before imaging. Because OCT does not require fixing, it can be used to image embryos in vivo and in utero. In this study, we compare the efficacy of OPT and OCT for imaging murine embryonic development. The data demonstrate the superior capability of OPT for imaging fine structures with high resolution in optically-cleared embryos while only OCT can provide structural and functional imaging of live embryos ex vivo and in utero with micrometer scale resolution.

Clinical Imaging with Optical Coherence Tomography

Epithelial cancers account for substantial mortality and are an important public health concern. With the need for earlier detection and treatment of these malignancies, the ability to accurately detect precancerous lesions has an increasingly important role in controlling cancer incidence and mortality. New optical technologies are capable of identifying early pathology in tissues or organs in which cancer is known to develop through stages of dysplasia, including the esophagus, colon, pancreas, liver, bladder, and cervix. These diagnostic imaging advances, together as a field known as optical endomicroscopy, are based on confocal microscopy, spectroscopy-based imaging, and optical coherence tomography (OCT), and function as “optical biopsies,” enabling tissue pathology to be imaged in situ and in real time without the need to excise and process specimens as in conventional biopsy and histopathology. Optical biopsy techniques can acquire high-resolution, cross-sectional images of tissue structure on the micron scale through the use of endoscopes, catheters, laparoscopes, and needles. Since the inception of these technologies, dramatic technological advances in accuracy, speed, and functionality have been realized. The current paradigm of optical biopsy, or single-area, point-based images, is slowly shifting to more comprehensive microscopy of larger tracts of mucosa. With the development of Fourier-domain OCT, also known as optical frequency domain imaging or, more recently, volumetric laser endomicroscopy, comprehensive surveillance of the entire distal esophagus is now achievable at speeds that were not possible with conventional OCT technologies. Optical diagnostic technologies are emerging as clinically useful tools with the potential to set a new standard for real-time diagnosis. New imaging techniques enable visualization of high-resolution, cross-sectional images and offer the opportunity to guide biopsy, allowing maximal diagnostic yields and appropriate staging without the limitations and risks inherent with current random biopsy protocols. However, the ability of these techniques to achieve widespread adoption in clinical practice depends on future research designed to improve accuracy and allow real-time data transmission and storage, thereby linking pathology to the treating physician. These imaging advances are expected to eventually offer a see-and-treat paradigm, leading to improved patient care and potential cost reduction.Virtual SlidesThe virtual slide(s) for this article can be found here:http://www.diagnosticpathology.diagnomx.eu/vs/5372548637202968

Objective To investigate the feasibility of using optical coherence tomography （OCT）in thy-roid surgery .Methods Surgical specimen including parathyroid gland , lymph nodes , adipose tissue and thyroid tissue from patients receiving thyroid surgery in Tianjin Medical University Cancer Institute and Hospital were col -lected.OCT images were collected and the results were compared with the routine examination .Results Para-thyroid glands , lymph nodes , adipose tissue , and thyroid tissue can be obtained high-resolution OCT images .Dif-ferent tissues and metastatic lymph node can be clearly distinguished .OCT imaging took about 1 minute and fro-zen examination cost about 25 minutes.Conclusions OCT is a time-saving, non-invasive and cross-sectional imaging technique .It can obtain clear structural images of the internal microstructure of bio-tissues.OCT technol-ogy used in thyroid surgery including parathyroid identification and determination of lymph node metastasis is fea -sible. Key words: Parathyroid; Optical coherence tomography; Lymph node

Transmission optical coherence tomography (tOCT) is gaining interest for imaging biological samples; however, so far, quantitative phase information has not been directly obtained. This study introduces SOPHAST-OCT, an approach for integrated 2D phase recovery in Off-Axis Full-Field Swept-Source tOCT. It uses phase-shifting to leverage OCT’s inherent phase changes between recorded interferograms. SOPHAST-OCT demonstrates promising phase agreement with the simulated ground truth phase. This approach represents a first step toward quantitative imaging in tOCT. Full Text: PDF References Y. Park, C. Depeursinge, G. Popescu, "Quantitative phase imaging in biomedicine", Nature Photon 12, 578 (2018). CrossRef K. Alm, H. Cirenajwis, L. Gisselsson, A.G. Wingren, B. Janicke, A. Mölder, et al., in Holography, Research and Technologies (IntechOpen, 2011). CrossRef W. Drexler, J. Fujimoto, editors , Optical Coherence Tomography: Technology and Applications, 2nd ed. (Springer Cham, 2015). CrossRef W. Krauze, P. Ossowski, M. Nowakowski, M. Szkulmowski, M. Kujawińska, "Enhanced QPI functionality by combining OCT and ODT methods", Quantitative Phase Imaging VII, 11653, 19 (2021). CrossRef B.C. Wilson, S.L. Jacques, "Optical reflectance and transmittance of tissues: principles and applications", IEEE J. Quantum Electron. 26, 2186 (1990). CrossRef J. van der Horst, A.K. Trull, J. Kalkman, "Deep-tissue label-free quantitative optical tomography", Optica 7, 1682 (2020). CrossRef P. Hosseini, Y. Sung, Y. Choi, N. Lue, Z. Yaqoob, P. So, "Scanning color optical tomography (SCOT)", Opt. Expr. 23, 19752 (2015). CrossRef P. de Groot, "Phase Shifting Interferometry" in Optical Measurement of Surface Topography, edited by R. Leach (Springer, Berlin, Heidelberg, 2011). CrossRef M. Wojtkowski, A. Kowalczyk, R. Leitgeb, A.F. Fercher, "Full range complex spectral optical coherence tomography technique in eye imaging", Opt. Lett. 27, 1415 (2002). CrossRef Q. Zhang, S. Zhong, J. Lin, W. Chen, M. Luo, J. Zhong, Y. Yu, Z. Peng, S. Cheng, "Full-range Fourier-domain optical coherence tomography based on Mach–Zehnder interferometer", Opt. Lasers Engin. 124, 105794 (2020). CrossRef R. Juarez-Salazar, C. Robledo-Sanchez, F. Guerrero-Sanchez, A. Rangel-Huerta, "Generalized phase-shifting algorithm for inhomogeneous phase shift and spatio-temporal fringe visibility variation", Opt. Express 22, 4738 (2014). CrossRef R. Juarez-Salazar, C. Robledo-Sánchez, C. Meneses-Fabian, F. Guerrero-Sánchez, L. M. Arévalo Aguilar, "Generalized phase-shifting interferometry by parameter estimation with the least squares method", Opt. Lasers Engin. 51, 626 (2013). CrossRef M.A. Herráez, D.R. Burton, M.J. Lalor, M.A. Gdeisat, "Fast two-dimensional phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path", Appl. Opt. 41, 7437 (2002). CrossRef Z. Wang, A.C. Bovik, "A universal image quality index", IEEE Signal Proc. Lett. 9, 81 (2002). CrossRef

In this paper we present, for the first time to our knowledge, the experimental results for determining suspension viscosity in a capillary type viscometer from flow velocity profiles measured by Doppler Optical Coherence Tomography. The suspension of 0.3?m polystyrene microspheres in a glycerol-water solution was used as a model fluid. The viscosity of the suspension was controlled by glycerol concentration. The shear rate and the shear stress at the capillary wall were measured at six flow rates. The corresponding viscosities were calculated. The comparison of the measured shear rates with the values calculated according to the flow rate of the syringe precision pump was performed. Additionally, the viscosities of the studied suspensions were measured by a rotational viscometer. Full Text: PDFReferences K.A. Hayes, M.R. buckley, I. Cohen, L.A. Archer, "High Resolution Shear Profile Measurements in Entangled Polymers", Phys. Rev. Lett. 101, 218301 (2008)[CrossRef] N. Willenbacher, H. Hanciogullari, H.G. Wagner, "High shear rheology of paper coating colors ? more than just viscosity", Chem. Eng. Technol. 20, 557 (1997)[CrossRef] M. Iotti, O.W. Gregersen, S. Moe, M. Lenes, "Rheological Studies of Microfibrillar Cellulose Water Dispersions", J. Polym. Environ. 19, 137 (2011)[CrossRef] M.T. Roberts, A. Mohraz, K.T. Christensen, J.A. Lewis, "Direct Flow Visualization of Colloidal Gels in Microfluidic Channels", Langmuir 23, 8726 (2007)[CrossRef] M. Schmidt, E. Wassner, H. Münstedt, "Setup and Test of a Laser Doppler Velocimeter for Investigations of Flow Behaviour of Polymer Melts", Mech. Time-Depend. Mater. 3, 371, (1999)[CrossRef] S. Schuberth, H. Münstedt, "Simultaneous measurements of velocity and stress distributions in polyisobutylenes using laser-Doppler velocimetry and flow induced birefringence", Rheol. Acta 47, 111 (2008)[CrossRef] Th. Wunderlich, P.O. Brunn, "A wall layer correction for ultrasound measurement in tube flow: comparison between theory and experiment", Flow Meas. Instrum. 11, 63 (2000)[CrossRef] J. Wiklund, I. Shahram, M. Stading, "Methodology for in-line rheology by ultrasound Doppler velocity profiling and pressure difference techniques", Chem. Eng. Sci. 62, 4277 (2007)[CrossRef] S. Yazdanfar, M.D. Kulkarni, J.A. Izatt, "High resolution imaging of in vivo cardiac dynamics using color Doppler optical coherence tomography", Opt. Express 1(13), 424 (1997)[CrossRef] Y. Zhao et al., "Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity", Opt. Lett. 25(2), 114 (2000)[CrossRef] J. Moger, S.J. Matcher C.P. Winlove, A. Shore, "Measuring red blood cell flow dynamics in a glass capillary using Doppler optical coherence tomography and Doppler amplitude optical coherence tomography", J. Biomed. Opt. 9(5), 982 (2004)[CrossRef] S. Tamborski et al., "Simultaneous analysis of flow velocity and spectroscopic properties of scattering media with the use of joint Spectral and Time domain OCT", Phot. Lett. Poland 1(2), 49 (2009) B. Povazay et al., "Submicrometer axial resolution optical coherence tomography", Opt. Lett. 27(20), 1800 (2002)[CrossRef] M. Harvey, T.A. Waigh, "Optical coherence tomography velocimetry in controlled shear flow", Phys. Rev. E 83, 031502 (2011)[CrossRef] J. Lauri, M. Wang, M. Kinnunen, R. Myllylä, "Measurement of microfluidic flow velocity profile with two Doppler optical coherence tomography systems", Proc. SPIE 6863, 68630F (2008)[CrossRef]

For the first time, the use of fiber-optic color Doppler optical coherence tomography (CDOCT) to map in vivo the three-dimensional (3-D) vascular network of airway segments in human lungs is demonstrated. Visualizing the 3-D vascular network in the lungs may provide new opportunities for detecting and monitoring lung diseases such as asthma, chronic obstructive pulmonary disease, and lung cancer. Our CDOCT instrument employs a rotary fiber-optic probe that provides simultaneous two-dimensional (2-D) real-time structural optical coherence tomography (OCT) and CDOCT imaging at frame rates up to 12.5 frames per second. Controlled pullback of the probe allows 3-D vascular mapping in airway segments up to 50 mm in length in a single acquisition. We demonstrate the ability of CDOCT to map both small and large vessels. In one example, CDOCT imaging allows assignment of a feature in the structural OCT image as a large (∼1 mm diameter) blood vessel. In a second example, a smaller vessel (∼80 μm diameter) that is indistinguishable in the structural OCT image is fully visualized in 3-D using CDOCT.