We present an advanced technique of polarized light microscopy (PLM) for the assessment of carious lesions, wherein the degree of polarization (DOP) is evaluated. Through modifications of a conventional PLM setup, images were generated by calculating the DOP from an image series of different linear polarization images acquired with a polarization camera. Demineralization is reliably displayed by the DOP in accordance with the common imaging methods. Evaluating the DOP by PLM allows the characterization of the different pathohistological zones of caries with a new quantitative approach.
Polarized light microscopy (PLM) is an established technique for the inspection of thin tooth sections in dental research. However, conventional PLM is mainly based on the qualitative evaluation of color-dependent birefringence, depolarization and transmittance but lacks a quantitative interpretation and, thus, the comparison with other polarimetric imaging methods. Here, we describe an easy to implement extension of PLM that enables measuring the degree of polarization (DOP). By replacing the analyzer and RGB camera in PLM with a monochrome polarization camera, linear polarization states can be directly determined from the transmitted light. Additionally rotating the polarizer in the illumination path and, by that, the state incident into the sample facilitates reconstructing a DOP image from multiple linear measurements. The resulting depolarization measurements are compared with conventional PLM images as well as X-ray micro-computed tomography (μCT) data of the intact teeth. Our results show that caries and demineralization appear to be directly related to depolarization in enamel. However, the interpretation is more complicated for dentin, which shows a reduced DOP also in sound tissue. We assume that these insights support the development and analysis of future dental polarimetry techniques in vivo, such as intra-oral polarization-sensitive optical coherence tomography (PS-OCT)
The collagen layer of the human Tympanic Membrane (TM), which is essential for sound conduction and hearing, can be assessed in vivo by using endoscopic Polarization-Sensitive Optical Coherence Tomography (PS-OCT), as we have shown recently. Since the resolution of the utilized system was limited, an ex vivo validation of the structural information is presented here. By comparing higher resolution PS-OCT images of a temporal bone specimen and Polarized Light Microscopy (PLM) of histological slices from that TM with picrosirius red staining, the microstructure is investigated.
Endoscopic Optical Coherence Tomography (OCT) enables the assessment of the eardrum and the middle ear in vivo. However, revealing the ossicles is often limited due to shadowing effects of preceding structures and the 3D impression is difficult to interpret. To compare the identified middle ear structures, OCT and cone-beam CT of a patient were spatially aligned and showed a good agreement in locating malleus and the promontory wall. As CT imaging uses ionizing radiation and is thus limited in application, we furthermore provide a concept how radiology can be utilized as a priori knowledge for OCT imaging. Therefore, a statistical shape model derived from μCT data of temporal bone specimens was fitted to in vivo OCT measurements, potentially providing a real-time augmentation of endoscopic OCT for middle ear diagnostics in the future.
SignificancePancreatic surgery is a highly demanding and routinely applied procedure for the treatment of several pancreatic lesions. The outcome of patients with malignant entities crucially depends on the margin resection status of the tumor. Frozen section analysis for intraoperative evaluation of tissue is still time consuming and laborious.AimWe describe the application of fiber-based attenuated total reflection infrared (ATR IR) spectroscopy for label-free discrimination of normal pancreatic, tumorous, and pancreatitis tissue. A pilot study for the intraoperative application was performed.ApproachThe method was applied for unprocessed freshly resected tissue samples of 58 patients, and a classification model for differentiating between the distinct tissue classes was established.ResultsThe developed three-class classification model for tissue spectra allows for the delineation of tumors from normal and pancreatitis tissues using a probability score for class assignment. Subsequently, the method was translated into intraoperative application. Fiber optic ATR IR spectra were obtained from freshly resected pancreatic tissue directly in the operating room.ConclusionOur study shows the possibility of applying fiber-based ATR IR spectroscopy in combination with a supervised classification model for rapid pancreatic tissue identification with a high potential for transfer into intraoperative surgical diagnostics.
SignificanceEndoscopic optical coherence tomography (OCT) is of growing interest for in vivo diagnostics of the tympanic membrane (TM) and the middle ear but generally lacks a tissue-specific contrast.AimTo assess the collagen fiber layer within the in vivo TM, an endoscopic imaging method utilizing the polarization changes induced by the birefringent connective tissue was developed.ApproachAn endoscopic swept-source OCT setup was redesigned and extended by a polarization-diverse balanced detection unit. Polarization-sensitive OCT (PS-OCT) data were visualized by a differential Stokes-based processing and the derived local retardation. The left and right ears of a healthy volunteer were examined.ResultsDistinct retardation signals in the annulus region of the TM and near the umbo revealed the layered structure of the TM. Due to the TM’s conical shape and orientation in the ear canal, high incident angles onto the TM’s surface, and low thicknesses compared to the axial resolution limit of the system, other regions of the TM were more difficult to evaluate.ConclusionsThe use of endoscopic PS-OCT is feasible to differentiate birefringent and nonbirefringent tissue of the human TM in vivo. Further investigations on healthy as well as pathologically altered TMs are required to validate the diagnostic potential of this technique.
Caries of the interdental space are usually difficult to detect with conventional bitewing radiography. We have developed an interdental probe for polarization-sensitive optical coherence tomography (PSOCT) that can distinguish between healthy and carious tooth structures. The development is based on a fiber optic probe with a compact motor design that allows volumetric imaging. In a clinical study, demineralization was detected using proximal PSOCT scans of premolars and molars, and compared with blind diagnoses from four dentists. The results show that PSOCT can detect both, early demineralization and advanced proximal caries, some of which could not be diagnosed with bitewing radiography.
Modern noninvasive imaging techniques are used in many areas of medical research, particularly where an additional modality is required to support close monitoring during pre- or post-care. In oral medicine, the combination of an experienced clinician and supporting noninvasive optical devices for oral imaging, such as optical coherence tomography (OCT), may ensure improved diagnosis. In this study, the pathological features of lichenoid oral mucosa were noninvasively imaged with our miniaturized pen-like OCT probe and compared to adjacent healthy areas. The non-homogeneous epithelial (EP) layer, increased cornification of the EP surface and unidentifiable basement membrane are the most important features recorded.
Imaging the collagen layer of the human tympanic membrane, on which the human hearing ability depends, is possible in vivo by using endoscopic polarization-sensitive optical coherence tomography (PSOCT), as we have shown recently. Since the resolution of the utilized system was limited, an ex vivo validation of the structural information is presented here. By comparing higher resolution PSOCT images of a temporal bone specimen and polarized light microscopy (PLM) of histological slices cut from the same sample and stained with picrosirius red, the microstructure is investigated. Besides matching PSOCT and PLM images, the methodical differences are discussed.
Endoscopic optical coherence tomography (OCT) enables the assessment of the eardrum and the middle ear in vivo. However, revealing the ossicles is often limited due to shadowing effects of preceding structures and the 3D impression is difficult to interpret. To compare the identified middle ear structures, OCT and cone-beam CT of a patient were spatially aligned and showed a good agreement in locating malleus and the promontory wall. As CT imaging uses ionizing radiation and is thus limited in application, we furthermore provide a concept how radiology can be utilized as a priori knowledge for OCT imaging. Therefore, a statistical shape model derived from μCT data of temporal bone specimens was fitted to in vivo OCT measurements, potentially providing a real-time augmentation of endoscopic OCT for middle ear diagnostics in the future.
Pancreatic surgery is a highly demanding and routinely applied procedure for the treatment of several pancreatic lesions. The outcome of patients with malignant entities crucially depends on the margin resection status of the tumor. In this study we describe the application of fiber-based attenuated total reflection infrared (ATR IR) spectroscopy for label-free discrimination of normal pancreatic, tumorous and pancreatitis tissue. The method was applied for the unprocessed freshly resected tissue samples of 40 patients, and a classification model for differentiating between the distinct tissue classes was established. The developed three-class classification model for tissue spectra allows the delineation of tumors from normal and pancreatitis tissues. The classification algorithm provides probability values for each sample to be assigned to normal, tumor or pancreatitis classes. The established probability values were transferred to a Red-Green-Blue (RGB) color plot. Subsequently, the method was translated into intraoperative application. Fiber optic ATR IR spectra were obtained from freshly resected pancreatic tissue directly in the operating room. The spectroscopic findings could subsequently be confirmed by the histology gold standard. This study shows the possibility of applying fiber-based ATR IR spectroscopy in combination with a supervised classification model for rapid pancreatic tissue identification with a high potential for transfer into intraoperative surgical diagnostics.
Domain walls (DWs) in ferroelectric materials are of highest interest as integrated functional elements, for instance in optoelectronic nanodevices. We investigated individual ferroelectric DWs in periodically-poled LiNbO3 single crystals by applying polarization-sensitive optical coherence tomography (PS-OCT). Comparing our experimental results with circular light polarization to simulations, we conclude that the three different signals recorded from each DW are associated to both the ordinary and extraordinary refractive index, and to a third contribution that arises from the mean value of the two. PS-OCT hence provides a valuable tool to probe the relevant electro-optical properties close to and at the DWs.
We present a miniaturized handheld OCT probe (9 grams weight), approximately the size of a small pen (10 mm x 140 mm), developed for use inside a patient’s mouth for examination of the oral mucosa. The probe operates in common-path mode and uses a magnetic scanning system to actuate a lensed fibre, achieving 50 B-scans per second. The system is demonstrated with OCT imaging of the buccal and alveolar mucosa of six patients with oral lichen planus (OLP) during clinical routine examination, and showed pathological changes in the tissue microarchitecture.
Optical coherence tomography (OCT) is a non-invasive, radiation-free optical technique for caries diagnosis. The presented study dealt with the correlation of conventional caries detection methods and using polarisation-sensitive OCT (PS-OCT). Human extracted carious teeth were assessed by dentists with visual and radiographic examination and PS-OCT images were gained. Proximal lesions could be detected early in the intensity-based OCT cross-sectional images. The degree of polarization can clearly delineate proximal caries from surrounding healthy tooth structure. The obtained results pave the way to reduce invasive filling therapy through early possibilities of intervention.
Endoscopic optical coherence tomography (eOCT), a depth-resolved, non-invasive, three-dimensional imaging technique, enables morphologic and functional examinations of the human tympanic membrane (TM) in vivo. To overcome the limitation of intensity-based OCT in tissue differentiation, light polarization is used here to assess collagen fibers as birefringent tissue. A fiber-based polarization-sensitive eOCT system was realized for first in vivo examinations of the TM’s collagen fiber layer, on which the acoustic and mechanical properties depend. By evaluating the local retardation, distinguishing the TM’s different tissues was possible and a comparison to microscopic ex vivo measurements was made.
Concerning the usage of non-invasive optical techniques for oral cancer detection, the presented study dealt with the manual and semi-automatic measurement of oral epithelial thickness by means of optical coherence tomography (OCT). Here, a total of 3,510 OCT images out of seven areas of the oral cavity was analyzed. In the result, epithelial thickness varied from 77 µm to 704 µm. Beyond that, there was a good correlation between both methods (ρ = 0.71-0.96). With regard to clinical routine use, manual epithelial thickness measurement could be beneficial due to a currently lower time investment with comparable precision.
Common-path probes provide considerable advantages for fiber-based OCT due to intrinsic length and phase matching. However, the polarization state of the reference light is usually arbitrary and variable due to stress-induced birefringence in single-mode fibers, which complicates implementing polarization-sensitive OCT. Here, we present depth-resolved retardation measurements with a single-mode fiber-based common-path probe by utilizing the constrained polarization evolution and the mirror state phenomenon for reconstruction of the round-trip measurements in the case of arbitrary reference states. Thus, a compact and flexible polarization-sensitive OCT implementation is demonstrated.
Depth-resolved retardation measurements with a single-mode fiber-based common-path probe by using polarization-sensitive optical coherence tomography are presented, utilizing the constrained polarization evolution and the mirror state phenomenon for reconstruction of the round-trip measurements.
Pathological alterations of the connective tissue, e.g. in succession of chronic otitis media, impair the acousto-mechanical function of the tympanic membrane (TM). Currently, none of the diagnostic techniques used in clinical practice assesses these tissue changes. By applying polarization-sensitive optical coherence tomography (PSOCT), a depth-resolved imaging technique providing additional tissue-specific contrast, local polarization changes of the fibrous layers of a human TM ex vivo were detected due to the birefringence of collagen fibers. Reconstructing and displaying local retardation from single-input PSOCT measurements enables to distinguish different tissue types which reveals the potential of PSOCT to extend conventional ENT diagnostics.
To date, there is still a lack of reliable imaging modalities to improve the quality of medical examinations of the oral mucosa in dentistry. One promising imaging technologies is optical coherence tomography (OCT). The present study provides in vivo intensity-based OCT cross sections of the human oral mucosa of the anterior and posterior oral cavity as well as the oropharynx of 47 disease-free adult volunteers. The randomized blinded image analysis was performed by means of 3,560 OCT cross sections using a set of seven qualitative and quantitative criteria to assess the epithelium and the lamina propria.
The prerequisite for a successful caries management is the early and precise detection of lesions. We have recently shown that depolarization imaging based on polarization-sensitive optical coherence tomography (PS-OCT) is a promising tool to detect demineralized enamel. To validate this contrast mechanism, we acquired data sets of tooth samples with occlusal caries lesions using PS-OCT and x-ray micro-computed tomography (µCT). Spatial alignment of the PS-OCT and µCT volumes was achieved by creating point clouds from surface segmentations, and subsequent registration. PS-OCT depolarization signals are in good agreement with the µCT results, showing the potential of this approach for caries diagnostics.
Optical coherence tomography (OCT) is a contactless and non-invasive imaging technique. Due to the high resolution of some 10 μm and the penetration depth of 1-2 mm in scattering tissue, OCT closes the gap between microscopy and sonography. Here, we present a GRIN-based endoscopic OCT (eOCT) system for middle ear diagnostics. EOCT combines the benefit of endoscopic imaging and the advantage of morphological and functional investigation of the tympanic membrane (TM). The eOCT system has a working distance of 10 mm, which results in a field-of-view of 10 mm. This allows a full three-dimensional visualization of the TM and surrounding tissue. In addition, the oscillation of the TM can be measured spatially resolved and in the frequency range between 500 Hz and 5000 Hz with 125 Hz resolution, which is realized by phase-resolved Doppler-OCT. First clinical results are demonstrated for one selected cases, a middle ear effusion.
While dental caries represents the major chronic disease of humans, visual and tactile inspection are the methods of choice in daily dental practice. Several optical technologies have been developed in recent years for the purpose of dental examination, including near-infrared light transillumination as a promising tool for the supplementation and partial replacement of radiography. In case of occlusal alterations, the incidence of surface discolorations impedes the visual assessment, whereas tactile inspection appears to yield little diagnostic information or might be detrimental. Optical coherence tomography (OCT) facilitates depth-resolved imaging with μm resolution, utilizing near-infrared light, and has already shown its potential for various dental applications. We have recently demonstrated that depolarization imaging utilizing the degree of polarization uniformity (DOPU) extends those abilities by the detection of early carious lesions, as it provides an unambiguous demineralization contrast. Here, we show that this approach also enables the assessment of occlusal enamel lesions in the presence of stains, and compare PS-OCT cross sections with polarized light microscopy (PLM) images of thin sections. For tooth samples with discoloration or demineralization, respectively, PS-OCT and PLM results are in good agreement.
The detection of incipient carious lesions is crucial for the preservation of dental hard tissue with preventive therapies. Optical coherence tomography (OCT) based imaging has been proofed to be a valuable methodology for the depth-resolved detection of alterations at dental hard tissue. Due to changes of birefringent properties at carious lesions, the measurement of polarization properties with polarization-sensitive OCT (PS-OCT) provides an additional contrast that could enhance the detection of incipient carious lesions. The aim of the present study was to monitor changes of polarization properties during the initial demineralization process by means of PS-OCT. Therefore, 18 bovine enamel palates were demineralized up to 7 weeks in an artificial demineralization model using lactate acid and buffer solution to mimic natural caries progression. The palates were stored at pH 5.5 and 35°C with constant fluid movement. In order to detect changes of depolarization at different stages of demineralization, the degree of polarization uniformity (DOPU) was calculated from PS-OCT measurements, performed under wet and dry conditions. In addition, polarization microscopy and micro-computed tomography of thin sections were analyzed to assess lesion depth and mineral loss. Our main finding is that consecutive stages of demineralization are correlated to an increasing DOPU contrast between sound enamel and the lesion area, where the lesion area is connected to decreasing DOPU values. Our results show that PS-OCT based imaging of birefringence changes is sensitive to very early stages of the demineralization process and adds a valuable contrast for the detection and monitoring of incipient enamel lesions.
An endoscopic optical coherence tomography (OCT) system with a wide field-of-view of 8 mm is presented, which combines the image capability of endoscopic imaging at the middle ear with the advantages of functional OCT imaging, allowing a morphological and functional assessment of the human tympanic membrane. The endoscopic tube has a diameter of 3.5 mm and contains gradient-index optics for simultaneous forward-viewing OCT and video endoscopy. The endoscope allows the three-dimensional visualization of nearly the entire tympanic membrane. In addition, the oscillation of the tympanic membrane is measured spatially resolved and in the frequency range between 500 Hz and 5 kHz with 125 Hz resolution, which is realized by phase-resolved Doppler OCT imaging during acoustical excitation with chirp signals. The applicability of the OCT system is demonstrated in vivo. Due to the fast image acquisition, structural and functional measurements are only slightly affected by motion artifacts.
The common way to diagnose hard and soft tissue irregularities in the oral cavity is initially the visual inspection by an experienced dentist followed by further medical examinations, such as radiological imaging and/or histopathological investigation. For the diagnosis of oral hard and soft tissues, the detection of early transformations is mostly hampered by poor visual access, low specificity of the diagnosis techniques, and/or limited feasibility of frequent screenings. Therefore, optical noninvasive diagnosis of oral tissue is promising to improve the accuracy of oral screening. Considering this demand, a rigid handheld endoscopic scanner was developed for optical coherence tomography (OCT). The novelty is the usage of a commercially near-infrared endoscope with fitting optics in combination with an established spectral-domain OCT system of our workgroup. By reaching a high spatial resolution, in vivo images of anterior and especially posterior dental and mucosal tissues were obtained from the oral cavity of two volunteers. The convincing image quality of the endoscopic OCT device is particularly obvious for the imaging of different regions of the human soft palate with highly scattering fibrous layer and capillary network within the lamina propria.
As dental caries is one of the most common diseases, the early and noninvasive detection of carious lesions plays an important role in public health care. Optical coherence tomography (OCT) with its ability of depth-resolved, high-resolution, noninvasive, fast imaging has been previously recognized as a promising tool in dentistry. Additionally, polarization sensitive imaging provides quantitative measures on the birefringent tissue properties and can be utilized for imaging dental tissue, especially enamel and dentin. By imaging three exemplary tooth samples ex vivo with proximal white spot, brown spot, and cavity, we show that the combination of polarization sensitive OCT and the degree of polarization uniformity (DOPU) algorithm is a promising approach for the detection of proximal carious lesions due to the depolarization contrast of demineralized tissue. Furthermore, we investigate different sizes of the DOPU evaluation kernel on the resulting contrast and conclude a suitable value for this application. We propose that DOPU provides an easy to interpret image representation and appropriate contrast for possible future screening applications in early caries diagnostics.
Since optical coherence tomography (OCT) provides three-dimensional high-resolution images of biological tissue, the benefit of polarization contrast in the field of dentistry is highlighted in this study. Polarization-sensitive OCT (PS OCT) with phase-sensitive recording is used for imaging dental and mucosal tissues in the human oral cavity in vivo. An enhanced polarization contrast of oral structures is reached by analyzing the signals of the co- and crosspolarized channels of the swept source PS OCT system quantitatively with respect to reflectivity, retardation, optic axis orientation, and depolarization. The calculation of these polarization parameters enables a high tissue-specific contrast imaging for the detailed physical interpretation of human oral hard and soft tissues. For the proof-of-principle, imaging of composite restorations and mineralization defects at premolars as well as gingival, lingual, and labial oral mucosa was performed in vivo within the anterior oral cavity. The achieved contrast-enhanced results of the investigated human oral tissues by means of polarization-sensitive imaging are evaluated by the comparison with conventional intensity-based OCT.
Recently, optical coherence tomography (OCT) was utilized in multiple studies for structural and functional imaging of the middle ear and the tympanic membrane. Since Doppler OCT allows both, the spatially resolved measurement of the tympanic membrane oscillation and high-resolution imaging, it is regarded as a promising tool for future in vivo applications. In this study, Doppler OCT is utilized for the visualization of the tympanic membrane oscillation in temporal bones with simulated Eustachian catarrh, which was realized by generating a depression in the tympanic cavity. The transfer function, meaning the oscillation amplitude normalized to the applied sound pressure, is measured frequency resolved in the range from 0.5 kHz to 6 kHz and with a lateral spatial resolution of 0.4 mm. Typical oscillation patterns could be observed in case of ambient pressure in the tympanic cavity. Under depression the characteristic oscillation patterns were observed with widely congruent appearance but at higher frequencies.
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