Growing Trend to Adopt Speckle Variance Optical Coherence Tomography for Biological Tissue Assessments in Pre-Clinical Applications.

Speckle patterns are a generic feature in coherent imaging techniques like optical coherence tomography (OCT). Although speckles are granular like noise texture, which degrades the image, they carry information that can be benefited by processing and thereby furnishing crucial information of sample structures, which can serve to provide significant important structural details of samples in in vivo longitudinal pre-clinical monitoring and assessments. Since the motions of tissue molecules are indicated through speckle patterns, speckle variance OCT (SV-OCT) can be well-utilized for quantitative assessments of speckle variance (SV) in biological tissues. SV-OCT has been acknowledged as a promising method for mapping microvasculature in transverse-directional blood vessels with high resolution in micrometers in both the transverse and depth directions. The fundamental scope of this article reviews the state-of-the-art and clinical benefits of SV-OCT to assess biological tissues for pre-clinical applications. In particular, focus on precise quantifications of in vivo vascular response, therapy assessments, and real-time temporal vascular effects of SV-OCT are primarily emphasized. Finally, SV-OCT-incorporating pre-clinical techniques with high potential are presented for future biomedical applications.

Development of a deviated focusing-based optical coherence microscope with a variable depth of focus for high-resolution imaging.

The aim of this study was to develop an optically deviated focusing-based variable depth-of-focus (DOF) oriented optical coherence microscopy (OCM) system to improve the DOF in high-resolution and precise focused imaging. In this study, an approach of varying beam diameter using deviated focusing was employed in the sample arm to enhance the DOF and to confirm precise focusing in OCM imaging. The optically deviated focusing technique was used to vary the focal point and DOF by altering the sample arm beam. The efficacy of the variable DOF imaging approach utilizing an optimized sample arm was confirmed by tissue-level imaging, where OCM images with varying DOF were obtained using deviated focusing. Experimentally confirmed lateral resolution of 2.19 µm was sufficient for the precise non-invasive visualization of abnormalities of fruit specimens. Thus, the proposed variable DOF-OCM system can be an alternative for precisely focused, high-resolution, and variable DOF imaging by improving the DOF in minimum lateral resolution variation.

Optical Coherence Tomography as a Non-Invasive Tool for Plant Material Characterization in Agriculture: A Review.

Characterizing plant material is crucial in terms of early disease detection, pest control, physiological assessments, and growth monitoring, which are essential parameters to increase production in agriculture and prevent unnecessary economic losses. The conventional methods employed to assess the aforementioned parameters have several limitations, such as invasive inspection, complexity, high time consumption, and costly features. In recent years, optical coherence tomography (OCT), which is an ultra-high resolution, non-invasive, and real-time unique image-based approach has been widely utilized as a significant and potential tool for assessing plant materials in numerous aspects. The obtained OCT cross-sections and volumetrics, as well as the amplitude signals of plant materials, have the capability to reveal vital information in both axial and lateral directions owing to the high resolution of the imaging system. This review discusses recent technological trends and advanced applications of OCT, which have been potentially adapted for numerous agricultural applications, such as non-invasive disease screening, optical signals-based growth speed detection, the structural analysis of plant materials, and microbiological discoveries. Therefore, this review offers a comprehensive exploration of recent advanced OCT technological approaches for agricultural applications, which provides insights into their potential to incorporate OCT technology into numerous industries.

On-field optical imaging data for the pre-identification and estimation of leaf deformities.

Visually nonidentifiable pathological symptoms at an early stage are a major limitation in agricultural plantations. Thickness reduction in palisade parenchyma (PP) and spongy parenchyma (SP) layers is one of the most common symptoms that occur at the early stage of leaf diseases, particularly in apple and persimmon. To visualize variations in PP and SP thickness, we used optical coherence tomography (OCT)-based imaging and analyzed the acquired datasets to determine the threshold parameters for pre-identifying and estimating persimmon and apple leaf abnormalities using an intensity-based depth profiling algorithm. The algorithm identified morphological differences between healthy, apparently-healthy, and infected leaves by applying a threshold in depth profiling to classify them. The qualitative and quantitative results revealed changes and abnormalities in leaf morphology in addition to disease incubation in both apple and persimmon leaves. These can be used to examine how initial symptoms are influenced by disease growth. Thus, these datasets confirm the significance of OCT in identifying disease symptoms nondestructively and providing a benchmark dataset to the agriculture community for future reference.

Non-destructive morphological observation of anatomical growth process in Haemaphysalis Longicornis tick specimens using optical coherence tomography.

BACKGROUND: Ticks are known as the representatives of hematophagous arachnids. They cause various tick-borne diseases, such as severe fever with thrombocytopenia syndrome (SFTS) and Lyme disease. To understand the mechanism of virus infection caused by ticks, morphology for the anatomical characteristics of crucial organs has been widely studied in acarological fields. The conventional methods used for tick observation have inevitable limitations. Dissection is the standard method to obtain the morphological information, and complex microscopy methods were utilized alternatively. OBJECTIVE: The study goal is to obtain the morphological information of ticks in different growth stages non-invasively. METHODS: Optical coherence tomography (OCT) is employed to acquire structural images of various internal organs without damage for observing the growth process of larva, nymph, and adult in Haemaphysalis longicornis ticks in real-time. RESULTS: Various internal organs, such as salivary glands, rectal sac, genital aperture, and anus, were well-visualized by the OCT enface and cross-sectional images, and the variation in size of these organs in each growth stage was compared quantitatively. CONCLUSIONS: Based on the obtained results, we confirmed the potential feasibility of OCT as a non-destructive real-time tool for morphological studies in acarology. Further research using OCT for acarological applications can include monitoring the growth process of ticks in terms of structural changes and investigating morphological differences between normal and virus-infected tick specimens.

Non-Invasive Optical Coherence Tomography Data-Based Quantitative Algorithm for the Assessment of Residual Adhesive on Bracket-Removed Dental Surface.

The aim of this study was to quantitatively assess the residual adhesive on orthodontic ceramic bracket-removed dental surface. In orthodontic process, ceramic bracket was repeated debonding physically, then the adhesive remained on the dental surface. The residual adhesive caused a lack of adhesive strength between dental and ceramic bracket. Since commonly used adhesive in orthodontics is translucent, residual adhesive is hard to be detected with conventional microscopes. Therefore, 1310 nm center wavelength swept-source OCT system based on laboratory customized image processing algorithm was used for the precise detection of residual adhesive on tooth surface. The algorithm separates residual adhesive from dental surface by comparing the height of adjacent B-scan images, while providing color-scaled images emphasizing the thickness information of residual adhesive. Finally, the acquired results were compared with microscopic and adhesive remnant index scoring gold standards, while the comparison confirmed the potential merits and the improvements of the proposed method over gold standards.

Integrated Quad-Scanner Strategy-Based Optical Coherence Tomography for the Whole-Directional Volumetric Imaging of a Sample.

Whole-directional scanning methodology is required to observe distinctive features of an entire physical structure with a three dimensional (3D) visualization. However, the implementation of whole-directional scanning is challenging for conventional optical coherence tomography (OCT), which scans a limited portion of the sample by utilizing unidirectional and bidirectional scanning methods. Therefore, in this paper an integrated quad-scanner (QS) strategy-based OCT method was implemented to obtain the whole-directional volumetry of a sample by employing four scanning arms installed around the sample. The simultaneous and sequential image acquisition capabilities are the conceptual key points of the proposed QS-OCT method, and were implemented using four precisely aligned scanning arms and applied in a complementary way according to the experimental criteria. To assess the feasibility of obtaining whole-directional morphological structures, a roll of Scotch tape, an ex vivo mouse heart, and kidney specimens were imaged and independently obtained tissue images at different directions were delicately merged to compose the 3D volume data set. The results revealed the potential merits of QS-OCT-based whole-directional imaging, which can be a favorable inspection method for various discoveries that require the dynamic coordinates of the whole physical structure.

A preliminary study of post-progressive nail-art effects on in vivo nail plate using optical coherence tomography-based intensity profiling assessment.

Nail beautification is a widely applied gender independent practice. Excessive nail beautifications and nail-arts have a direct impact on the nail structure and can cause nail disorders. Therefore, the assessment of post-progressive nail-art effects on the nail is essential to maintain optimal nail health and to avoid any undesirable disorders. In this study, in vivo nails were examined in control stage, with a nail-art stage, and after removing the nail-art stage using a 1310 nm spectral-domain optical coherence tomography (SD-OCT) system. The acquired cross-sectional OCT images were analyzed by a laboratory customized signal processing algorithm to obtain scattered intensity profiling assessments that could reveal the effects of nail beautification on the nail plate. The formation and progression of cracks on the nail plate surface were detected as an effect of nail beautification after 72 h of nail-art removal. Changes in backscattered light intensity and nail plate thickness of control and art-removed nails were quantitatively compared. The results revealed the potential feasibility of the developed OCT-based inspection procedure to diagnose post-progressive nail-art effects on in vivo nail plate, which can be helpful to prevent nail plate damages during art removal through real-time monitoring of the boundary between the nail plate and nail-art. Besides nail-art effects, the developed method can also be used for the investigation of nail plate abnormalities by examining the inconsistency of internal and external nail plate structure, which can be diagnosed with both qualitative and quantitative assessments from a clinical perspective.

Multi-directional Morphological Assessment of Single Bacterial Colonies Through Non-invasive Optical Imaging.

A bacterium in bacterial colony is a basal component of bacterial studies and is therefore of considerable importance. The morphological characteristics of a single colony have been widely used as the standard to identify diverse bacterial species. However, the conventional methods for obtaining morphological information, such as microscopic techniques, cannot provide tomographic views. This study utilizes spectral-domain optical coherence tomography (SD-OCT) to observe both external and internal structures for single colonies. OCT imaging provided a clear top (projection) and lateral (cross-sectional) images, which can identify distinct features in the fifteen different bacterial species examined. Through the acquired OCT images, the elevation type in each genus was confirmed, and the quantitative measurements for morphology including a diameter, height, and elevation angle were achieved. Moreover, the OCT raw data was used to build three-dimensional images to observe outer appearances in all direction. As a result, the averaged angles of 7.92°, 14.40°, 6.78°, and 11.92° of the genus Hymenobacter, Spirosoma, Bacillus, and Deinococcus, respectively, were calculated. In conclusion, we have demonstrated that OCT is a highly feasible, non-invasive method for the identification of bacterial species, providing detailed morphological and visual information. It thus has strong potential for applications in bacteriology, as well as biomedical and food sciences.

Optical Interferometric Fringe Pattern-Incorporated Spectrum Calibration Technique for Enhanced Sensitivity of Spectral Domain Optical Coherence Tomography.

Depth-visualizing sensitivity can be degraded due to imperfect optical alignment and non-equidistant distribution of optical signals in the pixel array, which requires a measurement of the re-sampling process. To enhance this depth-visualizing sensitivity, reference and sample arm-channeled spectra corresponding to different depths using mirrors were obtained to calibrate the spectrum sampling prior to Fourier transformation. During the process, eight interferogram patterns corresponding to point spread function (PSF) signals at eight optical path length differences were acquired. To calibrate the spectrum, generated intensity points of the original interferogram were re-indexed towards a maximum intensity range, and these interferogram re-indexing points were employed to generate a new lookup table. The entire software-based process consists of eight consecutive steps. Experimental results revealed that the proposed method can achieve images with a high depth-visualizing sensitivity. Furthermore, the results validate the proposed method as a rapidly performable spectral calibration technique, and the real-time images acquired using our technique confirm the simplicity and applicability of the method to existing optical coherence tomography (OCT) systems. The sensitivity roll-off prior to the spectral calibration was measured as 28 dB and it was halved after the calibration process.

Functional assessment of moisture influenced cadaveric tympanic membrane using phase shift-resolved optical Doppler vibrography.

An elevated relative moisture in the external ear canal and middle ear cavity may predispose to chronic otorrhea and related infections along with abnormal tympanic membrane (TM) vibration patterns. Therefore, phase shift-resolved optical Doppler vibrography (ODV) was used for vibration assessments of moisture influenced cadaveric TM. ODV was applied to generate time resolved cross-sectional and volumetric vibrographs of a cadaveric TM, driven acoustically at several frequencies. In order to analyze the effect of moisture on TM, homogenous moisture conditions were provided by soaking the cadaveric TM specimens in 1× phosphate buffer saline with a pH of 7.4. The TM specimen was exposed to a rapidly switchable frequency generator during the ODV image acquisition. The experiment was conducted for 3 hours and the cadaveric TM was exposed to each frequency with an interval of 30 minutes. Acquired phase shift-resolved ODV assessments revealed a depth dependent vibration tendency between the applied frequencies, along with a decline in the moisture level of the cadaveric TM specimen. Thus, the ODV method can aid our understanding of sound conduction in the middle ear, thus supporting the diagnosis of TM diseases.

In Situ Characterization of Micro-Vibration in Natural Latex Membrane Resembling Tympanic Membrane Functionally Using Optical Doppler Tomography.

Non-invasive characterization of micro-vibrations in the tympanic membrane (TM) excited by external sound waves is considered as a promising and essential diagnosis in modern otolaryngology. To verify the possibility of measuring and discriminating the vibrating pattern of TM, here we describe a micro-vibration measurement method of latex membrane resembling the TM. The measurements are obtained with an externally generated audio stimuli of 2.0, 2.2, 2.8, 3.1 and 3.2 kHz, and their respective vibrations based tomographic, volumetric and quantitative evaluations were acquired using optical Doppler tomography (ODT). The micro oscillations and structural changes which occurred due to diverse frequencies are measured with sufficient accuracy using a highly sensitive ODT system implied phase subtraction method. The obtained results demonstrated the capability of measuring and analyzing the complex varying micro-vibration of the membrane according to implied sound frequency.

Clinical Utility of Intraoperative Tympanomastoidectomy Assessment Using a Surgical Microscope Integrated with an Optical Coherence Tomography.

Significant technical and optical advances are required for intraoperative optical coherence tomography (OCT) to be utilized during otological surgeries. Integrating OCT with surgical microscopy makes it possible to evaluate soft tissue in real-time and at a high resolution. Herein, we describe an augmented-reality, intraoperative OCT/microscope system with an extended working distance of 280 mm, providing more space for surgical manipulation than conventional techniques. We initially performed ex vivo experiments to evaluate system performance. In addition, we validated the system by performing preliminary clinical assessments of tympanomastoidectomy outcomes in six patients with chronic otitis media. The system evaluated residual inflammation in the region-of-interest of the mastoid bone. Most importantly, the system intraoperatively revealed the connection between the graft and the remnant tympanic membrane. The extended working distance allows otological surgeons to evaluate the status of both the mastoid bone and tympanic membrane during manipulation, affording full intraoperative imaging.

Biophotonic approach for the characterization of initial bitter-rot progression on apple specimens using optical coherence tomography assessments.

The tremendous advances achieved in the biophotonics technologies have intensified the necessity for non-invasive modalities that can characterize diverse biological materials with increased sensitivity and resolution. Optical coherence tomography (OCT) is one of the techniques that has been applied for biological applications in medicine and agriculture to identify structural properties. Herein, we report the successful incorporation of OCT for the identification of morphological changes that occur as a result of the bitter rot disease, through continuous detection of structural changes. Detailed inner morphological structural changes occurring in fruit specimens were precisely analyzed as a function of the disease incubation period using OCT. The conducted histological correlation and quantitative three-dimensional evaluations provide a robust platform for further discoveries related to plant materials. The results highlight the initial identification of bitter rot progression on apple specimens owing to the non-invasive inspection capability of OCT. Therefore, we expect that the proposed method will enable immediate sensitivity improvements in the inspection of plant diseases for postharvest utility.

Non-Destructive Classification of Diversely Stained Capsicum annuum Seed Specimens of Different Cultivars Using Near-Infrared Imaging Based Optical Intensity Detection.

The non-destructive classification of plant materials using optical inspection techniques has been gaining much recent attention in the field of agriculture research. Among them, a near-infrared (NIR) imaging method called optical coherence tomography (OCT) has become a well-known agricultural inspection tool since the last decade. Here we investigated the non-destructive identification capability of OCT to classify diversely stained (with various staining agents) Capsicum annuum seed specimens of different cultivars. A swept source (SS-OCT) system with a spectral band of 1310 nm was used to image unstained control C. annuum seeds along with diversely stained Capsicum seeds, belonging to different cultivar varieties, such as C. annuum cv. PR Ppareum, C. annuum cv. PR Yeol, and C. annuum cv. Asia Jeombo. The obtained cross-sectional images were further analyzed for the changes in the intensity of back-scattered light (resulting due to dye pigment material and internal morphological variations) using a depth scan profiling technique to identify the difference among each seed category. The graphically acquired depth scan profiling results revealed that the control specimens exhibit less back-scattered light intensity in depth scan profiles when compared to the stained seed specimens. Furthermore, a significant back-scattered light intensity difference among each different cultivar group can be identified as well. Thus, the potential capability of OCT based depth scan profiling technique for non-destructive classification of diversely stained C. annum seed specimens of different cultivars can be sufficiently confirmed through the proposed scheme. Hence, when compared to conventional seed sorting techniques, OCT can offer multipurpose advantages by performing sorting of seeds in respective to the dye staining and provides internal structural images non-destructively.

In Vivo Non-Destructive Monitoring of Capsicum Annuum Seed Growth with Diverse NaCl Concentrations Using Optical Detection Technique.

We demonstrate that optical coherence tomography (OCT) is a plausible optical tool for in vivo detection of plant seeds and its morphological changes during growth. To investigate the direct impact of salt stress on seed germination, the experiment was conducted using Capsicum annuum seeds that were treated with different molar concentrations of NaCl. To determine the optimal concentration for the seed growth, the seeds were monitored for nine consecutive days. In vivo two-dimensional OCT images of the treated seeds were obtained and compared with the images of seeds that were grown using sterile distilled water. The obtained results confirm the feasibility of using OCT for the proposed application. Normalized depth profile analysis was utilized to support the conclusions.

Non-Destructive Analysis of the Internal Anatomical Structures of Mosquito Specimens Using Optical Coherence Tomography.

The study of mosquitoes and analysis of their behavior are of crucial importance in the on-going efforts to control the alarming increase in mosquito-borne diseases. Furthermore, a non-destructive and real-time imaging technique to study the anatomical features of mosquito specimens can greatly aid the study of mosquitoes. In this study, we demonstrate the three-dimensional imaging capabilities of optical coherence tomography (OCT) for structural analysis of Anopheles sinensis mosquitoes. The anatomical features of An. sinensis head, thorax, and abdominal regions, along with the morphology of internal structures, such as foregut, midgut, and hindgut, were studied using OCT imaging. Two-dimensional and three-dimensional OCT images, used in conjunction with histological images, proved useful for anatomical analysis of mosquito specimens. By presenting this work as an initial study, we demonstrate the applicability of OCT for future mosquito-related entomological research, and also in identifying changes in mosquito anatomical structure.

Optical coherence tomography-integrated, wearable (backpack-type), compact diagnostic imaging modality for in situ leaf quality assessment: publisher's note.

This note points out additional funding that was not added to Appl. Opt.56, D108 (2017)APOPAI0003-693510.1364/AO.56.00D108.

Optical coherence tomography-integrated, wearable (backpack-type), compact diagnostic imaging modality for in situ leaf quality assessment.

We developed a compact, wearable diagnostic imaging modality employing optical coherence tomography for in situ plant leaf quality assessments. This system is capable of diagnosing infected leaves at the initial disease stages. Our system is a versatile backpack-type imaging modality with a compact spectrometer, miniature computer, rechargeable power source, and handheld inspection probe. This method enhances real-time in situ specimen inspection through direct implementation of the imaging modality in a plantation. To evaluate the initial performance, field experiments were conducted in apple, pear, and persimmon plantations. Based on the obtained results, we can conclude that the developed imaging modality can be considered as a promising, efficient, convenient, and fast in situ inspection technique for various agricultural fields, which minimizes the limitations of complex tabletop inspection modalities.

Optical sensing method to analyze germination rate of Capsicum annum seeds treated with growth-promoting chemical compounds using optical coherence tomography.

Seed germination rate differs based on chemical treatments, and nondestructive measurements of germination rate have become an essential requirement in the field of agriculture. Seed scientists and other biologists are interested in optical sensing technologies-based biological discoveries due to nondestructive detection capability. Optical coherence tomography (OCT) has recently emerged as a powerful method for biological and plant material discoveries. We report an extended application of OCT by monitoring the germination rate acceleration of chemically primed seeds. To validate the versatility of the method, Capsicum annum seeds were primed using three chemical compounds: sterile distilled water (SDW), butandiol, and 1-hexadecene. Monitoring was performed using a 1310-nm swept source OCT system. The results confirmed more rapid morphological variations in the seeds treated with 1-hexadecene medium than the seeds treated with SDW and butandiol within 8 consecutive days. In addition, fresh weight measurements (gold standard) of seeds were monitored for 15 days, and the obtained results were correlated with the OCT results. Thus, such a method can be used in various agricultural fields, and OCT shows potential as a rigorous sensing method for selecting the optimal plant growth-promoting chemical compounds rapidly, when compared with the gold standard methods.