Deep tissue imaging by optical coherence tomography / microscopy at Optical Window III

Optical coherence tomography (OCT) is a non-invasive cross-sectional imaging technique with micrometer resolution. OCT is useful, non-invasive imaging technique of the internal structure, and it has been applied in many fields, especially medicine and industry. The theoretical axial resolution is determined by the center wavelength and bandwidth of the light source, and the wider the bandwidth is, the higher the axial resolution is. Supercontinuum is the high-power, ultrawideband light source. We have been investigating ultrahigh-resolution (UHR)-OCT using supercontinuum. The characteristics of OCT imaging depend on the optical wavelength used. In this talk, we report our recent work of the wavelength dependence of UHR-OCT using a supercontinuum for biomedical imaging. In order to investigate the wavelength dependence of UHR-OCT, the wideband, high-power, low-noise supercontinua were generated at wavelengths of 0.8, 1.1, 1.3, and 1.7 um based on ultrashort pulses and nonlinear fibers. The wavelength dependence of OCT imaging was examined quantitatively using biological phantoms. Ultrahigh-resolution imaging of a rat lung was demonstrated with wavelengths of 0.8 – 1.0 um UHR-OCT. The variation of alveolar volume was estimated using 3D image analysis. We also developed UHR-spectral domain-OCT and optical coherence microscopy (OCM) at 1.7 um. The high-resolution and high-penetration imaging of turbid tissue, especially mouse brain, was demonstrated. The wavelength dependence of OCM was also discussed in terms of mouse brain imaging.

Optical coherence tomography (OCT) is a noninvasive cross-sectional imaging technique with micrometer resolution. The theoretical axial resolution is determined by the center wavelength and bandwidth of the light source, and the wider the bandwidth, the higher the axial resolution. The characteristics of OCT imaging depend on the optical wavelength used. In this paper, we investigated the wavelength dependence of ultrahigh-resolution (UHR) OCT using a supercontinuum for biomedical imaging. Wideband, high-power, low-noise supercontinua (SC) were generated at λ = 0.8, 1.1, 1.3, and 1.7 μ m based on ultrashort pulses and nonlinear fibers. The wavelength dependence of OCT imaging was examined quantitatively using biological phantoms. Ultrahigh-resolution imaging of a rat lung was demonstrated with λ = 0.8–1.0 μ m UHR-OCT. The variation of alveolar volume was estimated using three-dimensional image analysis. Finally, UHR-spectral domain-OCT and optical coherence microscopy at 1.7 μ m were developed, and high-resolution and high-penetration imaging of turbid tissue, especially mouse brain, was demonstrated.

We quantitatively investigated the image quality in deep tissue imaging with optical coherence microscopy (OCM) in the 1700 nm spectral band, in terms of the signal-to-background ratio (SBR) and lateral resolution. In this work, to demonstrate the benefits of using the 1700 nm spectral band for OCM imaging of brain samples, we compared the imaging quality of OCM en-face images obtained at the same position by using a hybrid 1300 nm/1700 nm spectral domain (SD) OCM system with shared sample and reference arms. By observing a reflective resolution test target through a 1.5 mm-thick tissue phantom, which had a similar scattering coefficient to brain cortex tissue, we confirmed that 1700 nm OCM achieved an SBR about 6-times higher than 1300 nm OCM, although the lateral resolution of the both OCMs was similarly degraded with the increase of the imaging depth. Finally, we also demonstrated high-contrast deep tissue imaging of a mouse brain at a depth up to 1.8 mm by using high-resolution 1700 nm SD-OCM.

OCT-A is becoming more popular in recent years and there is a high demand to improve the quality of angiograms as well as to extract quantitative information. We applied various processing methods for microvasculature enhancement like Hessian-Frangi to a data set obtained with Bessel and Gaussian OCT systems. We used angiogenesis, fractal and multifractal analysis to extract more quantitative information. We applied the processing methods for healthy, stroke, tumor progression and the results of enhanced processing and quantitative analysis for those are presented in this letter. Full Text: PDF ReferencesJ. G. Fujimoto, C. Pitris, S. A. Boppart, and M. E. Brezinski, "Optical coherence microscopy as a novel, non-invasive method for the 4D live imaging of early mammalian embryos", Neoplasia (New York, NY), 2000, 2(1-2):9-25 CrossRef O. Liba, E. D. SoRelle, D. Sen, and A. de la Zerda, "Contrast-enhanced optical coherence tomography with picomolar sensitivity for functional in vivo imaging", Sci Rep. 2016, 6(1):23337. CrossRef O Liba, M. D. Lew, E. D. SoRelle, et al., "Speckle-modulating optical coherence tomography in living mice and humans", Nat Commun. 2017, 8:15845. CrossRef K. Karnowski, A. Ajduk, B. Wieloch, et al., "Optical coherence microscopy as a novel, non-invasive method for the 4D live imaging of early mammalian embryos", Sci Rep. 2017, 7(1):4165. CrossRef V. J. Srinivasan, S. Sakadžić, I. Gorczynska, et al., "Quantitative cerebral blood flow with Optical Coherence Tomography", Opt Express. 2010, 18(3):2477. CrossRef S. Tamborski, H. C. Lyu, H. Dolezyczek, et al. Extended-focus optical coherence microscopy for high-resolution imaging of the murine brain. Biomed Opt Express. 2016, 7(11):4400-4414. CrossRef A. F. Frangi, W. J. Niessen, K. L. Vincken, and M. A. Viergever, "Multiscale vessel enhancement filtering", Lect Notes Comput Sc. 1998;1496:130–137 CrossRef A. A. Ucuzian, A. A. Gassman, A. T. East, and H. P. Greisler , Journal of burn care & research: official publication of the American Burn Association 2010 , 31(1):158. CrossRef R. Lopes, and Betrouni, N. (2009). "Fractal and multifractal analysis: A review", Med. Image Anal. 13, 634–649. CrossRef J. W. Baish and R. K. Jain., "Correspondence re: J. W. Baish and R. K. Jain, Fractals and Cancer. Cancer Res., 60: 3683-3688, 2000.", Cancer Res. 2000, Jul 15, 60(14):3683-8. DirectLink

Optical coherence microscopy (OCM) is a high-resolution imaging technique based on optical coherence tomography and confocal microscopy. The recent studies on OCM operating at 800-1300 nm spectral region have shown that OCM enables to visualize micrometer- or sub-micrometer-scale structures of animal tissues. Although OCMs offers such high-resolution label-free imaging capability of animal tissues, the imaging depth was restricted by multiple light scattering and light absorption of water in samples. Here, for high-resolution deep-tissue imaging, we developed an OCM in the 1700-nm spectral band by using a supercontinuum (SC) source with a Gaussian-like spectral shape in the wavelength region. Recently, it has been reported that the 1700-nm spectral band is a promising choice for enhancing the imaging depth in the observation of turbid scattering tissues because of the low attenuation coefficient of light. In this study, to clarify that the 1700-nm OCM has a potential to realize the enhanced imaging depth, we compared the attenuation of the signal-to-noise ratio between the 1700-nm and 1300-nm OCM imaging of a mouse brain under the same signal detection sensitivity condition. The result shows that the 1700-nm OCM enables us to achieve the enhanced imaging depth. In this 1700-nm OCM, we also confirmed that the lateral resolution of 1.3 µm and axial resolution of 2.8 µm in tissue were achieved.

In recent years, optical coherence tomography (OCT) became gained importance in medical disciplines like ophthalmology, due to its noninvasive optical imaging technique with micrometer resolution and short measurement time. It enables e. g. the measurement and visualization of the depth structure of the retina. In other medical disciplines like dermatology, histopathological analysis is still the gold standard for skin cancer diagnosis. The EU-funded project VIAMOS (Vertically Integrated Array-type Mirau-based OCT System) proposes a new type of OCT system combined with micro-technologies to provide a hand-held, low-cost and miniaturized OCT system. The concept is a combination of full-field and full-range swept-source OCT (SS-OCT) detection in a multi-channel sensor based on a micro-optical Mirau-interferometer array, which is fabricated by means of wafer fabrication. This paper presents the study of an experimental proof-of-concept OCT system as a one-channel sensor with bulk optics. This sensor is a Linnik-interferometer type with similar optical parameters as the Mirau-interferometer array. A commercial wavelength tunable light source with a center wavelength at 845nm and 50nm spectral bandwidth is used with a camera for parallel OCT A-Scan detection. In addition, the reference microscope objective lens of the Linnik-interferometer is mounted on a piezo-actuated phase-shifter. Phase-shifting interferometry (PSI) techniques are applied for resolving the conjugate complex artifact and consequently contribute to an increase of image quality and depth range. A suppression ratio of the complex conjugate term of 36 dB is shown and a system sensitivity greater than 96 dB could be measured.

Optical coherence tomography (OCT) is a new technique for micron scale, cross-sectional, tomographic imaging.1 In biology and medicine, OCT can be a powerful technique for optical biopsy because it permits the direct imaging of cross-sectional tissue architectural morphology without the need to excisionally remove specimens. OCT imaging is somewhat analogous to radar or ultrasound, except that OCT uses a low coherence optical source and interferometry to perform time delay measurement of light which is backreflected or backscattered from optically turbid specimens. Superluminescent diodes can provide 15-20 micron resolution imaging at several fixed wavelengths, including 800 and 1300 nm, but output powers are limited to the order of a milliwatt. Studies at these wavelengths have demonstrated that 1300 nm wavelengths can achieve greater imaging penetration depths in biological tissues because of reduced scattering. Ultrahigh resolution imaging has been demonstrated using the fluorescent emission from solid state laser media2 and femtosecond pulses from a mode locked Ti:Al2O3 laser.3 OCT using mode locked solid state lasers3 is especially promising because the high output powers available enable higher signal to noise levels as well as faster data acquisition. Using a mode locked source, OCT imaging rates approaching real time can be achieved. In addition, the spectral bandwidth of femtosecond pulses can be broadened by using self phase modulation in an optical fiber thus yielding significant increases in imaging resolution. In this paper we present a Kerr lens mode locked Forsterite laser (at 1.3 micron wavelength) which is spectrally broadened through self-phase modulation in a dispersion shifted fiber. With this source 5.7 micron resolution OCT images with 116 dB signal to noise are demonstrated. Applications of mode locked solid state technology for OCT biomedical imaging is discussed.

Optical coherence tomography (OCT) is a non-invasive optical imaging technique with a micrometer resolution that may potentially offer real-time bedside imaging of sufficient detail to allow for morphological discrimination between different types of bullae. To explore the potential of OCT in bullous skin disorders by looking at a set of patients with skin blisters of known origin and study the OCT images for possible hallmarks of the blistering level. OCT provides cross-sectional, tomographic images of the skin. A consecutive series of patients were recruited and their lesions imaged by OCT: 3 patients with bullous pemphigoid (BP), 1 patient with extensive bullae following burns, 1 patient with pemphigus, 1 patient with subcorneal pustular dermatosis, and a patient with Dariers disease. The latter two were included due to similarity to pemphigus with respect to the level of defect cell adhesion. In OCT images, BP bullae are easily depicted as dark, ovoid to round well-demarquated areas, and BP bulla morphology is clearly different from the burn blisters and the pemphigus-like disease with respect to the blistering level. Differentiation of epidermal and subepidermal blisters is demonstrated using OCT. The variation within pemphigoid lesions and pemphigus-like diseases is however too subtle to allow for differential diagnosis; this may be ascribed to limited resolution. Enhanced resolution of OCT may overcome this obstacle.

Towards high resolution imaging of human airways with optical coherence microscopy

Optical coherence microscopy (OCM) has unique advantages of high-resolution volumetric imaging without relying on exogenous labels or dyes. It combines the coherence-gated depth discrimination of optical coherence tomography (OCT) with the high lateral resolution of confocal microscopy, offering an excellent balance between the resolutions and imaging depth. However, as the lateral resolution becomes higher, the imaging depth of OCM decreases and its three-dimensional imaging capability is greatly degraded. To overcome this limitation, we used amplitude apodization to create quasi-Bessel beam illumination in order to extend the depth of focus. The lateral and axial resolutions of our OCM system were measured to be 1.6 μm and 2.9 μm in tissue. The imaging depth was extended by ~3.0X (~100 μm) beyond that of the standard Gaussian beam OCM. Using zebrafish embryos as a test system, we demonstrate extendedfocus OCM for structural imaging studies, which revealed the detailed anatomy deep in embryos.

BackgroundEarly diagnosis of non-melanoma skin cancer (NMSC) is potentially possible using optical coherence tomography (OCT) which provides non-invasive, real-time images of skin with micrometre resolution and an imaging depth of up to 2mm. OCT technology for skin imaging has undergone significant developments, improving image quality substantially. The diagnostic accuracy of any method is influenced by continuous technological development making it necessary to regularly re-evaluate methods. ObjectiveThe objective of this study is to estimate the diagnostic accuracy of OCT in basal cell carcinomas (BCC) and actinic keratosis (AK) as well as differentiating these lesions from normal skin. MethodsA study set consisting of 142 OCT images meeting selection criterea for image quality and diagnosis of AK, BCC and normal skin was presented uniformly to two groups of blinded observers: 5 dermatologists experienced in OCT-image interpretation and 5 dermatologists with no experience in OCT. During the presentation of the study set the observers filled out a standardized questionnaire regarding the OCT diagnosis. Images were captured using a commercially available OCT machine (Vivosight ®, Michelson Diagnostics, UK). ResultsSkilled OCT observers were able to diagnose BCC lesions with a sensitivity of 86% to 95% and a specificity of 81% to 98%. Skilled observers with at least one year of OCT-experience showed an overall higher diagnostic accuracy compared to inexperienced observers. ConclusionsThe study shows an improved diagnostic accuracy of OCT in differentiating AK and BCC from healthy skin using state-of-the-art technology compared to earlier OCT technology, especially concerning BCC diagnosis.

To investigate optical coherence microscopy (OCM) imaging features and the application value of these high-resolution images for identifying endocervical canal lesions (ECLs), which is a clinical dilemma in cervical cancer screening programs. In total, 520 OCM images were obtained by scanning the cervical canal lesions with an ultra-high-resolution OCM system (204 specimens from 73 patients). The OCM morphologic characteristics of ECLs were observed and summarized, and then 3 researchers performed a diagnostic test of OCM images of cervical canal lesions. The accuracy, sensitivity, specificity, positive predictive value, negative predictive value, 95% confidence interval of each parameter, and interinvestigator agreement (κ) were calculated. Normal endocervix, cysts, squamous metaplasia, high-grade squamous intraepithelial lesions involving glands, and invasive carcinoma had distinct OCM characteristics, which correlated well with corresponding H&E histologic sections. The accuracy, sensitivity, and specificity of the 3 researchers were 90.6%, 89.3% (95% CI, 86.5%-91.7%) and 91.6% (95% CI, 89.2%-93.5%), respectively. The positive predictive value was 90.1% (95% CI, 87.3%-92.4%), and the negative predictive value was 90.9% (95% CI, 88.5%-92.9%), with almost perfect agreement (κ = 0.874). The application of the OCM system in cervical canal lesions is feasible and could help improve detection of occult ECLs in cervical cancer screening programs. This study lays the foundation for further research on OCM in cervical canal lesions in vivo, which also has a potential impact on projecting pathologic evaluation beyond what is currently possible, perhaps globally.

Microaneurysms (MAs) are pathognomonic signs that help clinicians to detect diabetic retinopathy (DR) in the early stages. Automatic detection of MA in retinal images is an active area of research due to its application in screening processes for DR which is one of the main reasons of blindness amongst the working-age population. The focus of these works is on the automatic detection of MAs in en face retinal images like fundus color and Fluorescein Angiography (FA). On the other hand, detection of MAs from Optical Coherence Tomography (OCT) images has 2 main advantages: first, OCT is a non-invasive imaging technique that does not require injection, therefore is safer. Secondly, because of the proven application of OCT in detection of Age-Related Macular Degeneration, Diabetic Macular Edema, and normal cases, thanks to detecting MAs in OCT, extensive information is obtained by using this imaging technique. In this research, the concentration is on the diagnosis of MAs using deep learning in the OCT images which represent in-depth structure of retinal layers. To this end, OCT B-scans should be divided into strips and MA patterns should be searched in the resulted strips. Since we need a dataset comprising OCT image strips with suitable labels and such large labelled datasets are not yet available, we have created it. For this purpose, an exact registration method is utilized to align OCT images with FA photographs. Then, with the help of corresponding FA images, OCT image strips are created from OCT B-scans in four labels, namely MA, normal, abnormal, and vessel. Once the dataset of image strips is prepared, a stacked generalization (stacking) ensemble of four fine-tuned, pre-trained convolutional neural networks is trained to classify the strips of OCT images into the mentioned classes. FA images are used once to create OCT strips for training process and they are no longer needed for subsequent steps. Once the stacking ensemble model is obtained, it will be used to classify the OCT strips in the test process. The results demonstrate that the proposed framework classifies overall OCT image strips and OCT strips containing MAs with accuracy scores of 0.982 and 0.987, respectively.

Optical coherence microscopy (OCM) is a non-destructive 3-dimentional (3D) imaging technique with micrometer-scale resolution, which is based on optical coherence tomography (OCT) and confocal microscopy [1-3]. Recently, it has been demonstrated that the OCT imaging depth is improved by using 1700 nm spectral band, so called “optical window 3”, due to the lower light absorption and a local minimum of water absorption in the wavelength region [4-8]. In our group, we developed a supercontinuum (SC) laser source at the 1700-nm wavelength region and demonstrated that 1700-nm OCT allows us to visualize the structures of mouse brain at a depth up to 1.7 mm [9-11]. We also successfully demonstrated 3D highresolution visualization of myelinated axons in a mouse brain with 1700-nm OCM, which we developed based on a time-domain low-coherence interferometer [12]. In this presentation, we report high-resolution spectral-domain OCM (SD-OCM) at the 1700-nm spectral band for improving the imaging acquisition speed of 1700-nm OCM.

Optical coherence microscopy (OCM) is a novel technique complementary to optical coherence tomography (OCT) which combines low-coherence interferometry with confocal microscopy to achieve micron-scale resolution imaging in highly scattering media. OCM may be implemented using a single-mode fiber-optic low-coherence interferometer (See Fig. 1). A high numerical aperture objective is used to focus sample-arm light into the specimen, and the reference arm length of the interferometer is adjusted to match the sample arm focal plane optical depth. The sample arm of the interferometer comprises a scanning confocal microscope, in which either the sample or the probe beam is laterally scanned in a raster pattern, and the optical fiber acts as a single-mode confocal aperture for combined light illumination and collection. The reference arm length of the interferometer establishes the depth position of an interferometric “coherence gate” in the sample, from which backscattered light is preferentially collected. Initial studies of OCM in scattering phantoms have demonstrated that this technique provides increased optical sectioning depth compared to confocal microscopy alone.