Optical Coherence Tomography Tomograms Research Articles

Signal-Decay Based Approach for Visualization of Buried Defects in 3-D Printed Ceramic Components Imaged with Help of Optical Coherence Tomography.

We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) processes. The OCT tomograms obtained on the green samples showed the capability of the method to visualize variations in the layered structure of the samples as well as the presence of cracks and inclusions at depths up to 130 µm, as validated by SEM images. The structural information was visible in cross-sectional images as well as in plan-view images. The optical signal measured from the printed zirconia oxide and titanium oxide samples showed strong attenuation with depth and could be fit with an exponential decay curve. The variations of the decay parameter correlated very well with the presence of defects and material variation. When used as an imaging quantity, the decay parameter projects the position of the defects into 2-D (X,Y) coordinates. This procedure can be used in real time, it reduces the data volume up to 1000 times, and allows for faster subsequent data analysis and transfer. Tomograms were also obtained on sintered samples. The results showed that the method can detect changes in the optical properties of the green ceramics caused by sintering. Specifically, the zirconium oxide samples became more transparent to the light used, whereas the titanium suboxide samples became entirely opaque. In addition, the optical response of the sintered zirconium oxide showed variations within the imaged volume, indicating material density variations. The results presented in this study show that OCT provides sufficient structural information on 3-D-printed ceramics and can be used as an in-line tool for quality control.

Choroidal melanoma and retinal changes

To study the capabilities of optical coherence tomography (OCT) in terms of finding the ways CM spreads into the retina based on pathomorphological examination of the eyes enucleated due to CM. OCT tomograms of 64 eyes with CM (mean tumor elevation - 2.89±0.19 mm, diameter - 9.58±0.43 mm) were studied. Pathomorphological study was conducted on 18 eyes with CM elevated by up to 7 mm and without previous treatment. OCT revealed signs of melanoma invading into the retina in 49 eyes. Among those signs were: presence of retina/CM aggregation (21 eyes), tearing of Bruch's membrane and retinal pigment epithelium, disturbed differentiation of outer retinal layers (15 eyes). Combination of two types of invasion was found in 11 eyes. Pathomorphological study showed low mitotic activity of CM and the presence of a small number of fine-local necroses and hemorrhages. Invasion of CM into the retina was determined in 13 eyes. Retinal invasion began with local destruction of Bruch's membrane (BM) and was often limited by the photoreceptor level, disturbing architectonics of the retina and nuclear layers. Large CMs were accompanied by rough destruction of the Bruch's membrane, tumor cells - in the edematous retina with cystoid dystrophy, in its inner layers, invading into the vitreous body. Infiltration of the retina to inner nuclear layer was accompanied by its transudative detachment and cystoid dystrophy. Invasion of CM into the retina affecting all of its layers imposes use of OCT to examine the integrity of the retina, even with a tumor of small thickness. Tumoral infiltration of the retina and localization of tumor near the optic disc are two contraindications for local endovitreal resection. Brachytherapy requires consideration of tumor characteristics and thickness of the retina for calculation of apical radiation dose.

Noise-compensated homotopic non-local regularized reconstruction for rapid retinal optical coherence tomography image acquisitions.

BackgroundOptical coherence tomography (OCT) is a minimally invasive imaging technique, which utilizes the spatial and temporal coherence properties of optical waves backscattered from biological material. Recent advances in tunable lasers and infrared camera technologies have enabled an increase in the OCT imaging speed by a factor of more than 100, which is important for retinal imaging where we wish to study fast physiological processes in the biological tissue. However, the high scanning rate causes proportional decrease of the detector exposure time, resulting in a reduction of the system signal-to-noise ratio (SNR). One approach to improving the image quality of OCT tomograms acquired at high speed is to compensate for the noise component in the images without compromising the sharpness of the image details.MethodsIn this study, we propose a novel reconstruction method for rapid OCT image acquisitions, based on a noise-compensated homotopic modified James-Stein non-local regularized optimization strategy. The performance of the algorithm was tested on a series of high resolution OCT images of the human retina acquired at different imaging rates.ResultsQuantitative analysis was used to evaluate the performance of the algorithm using two state-of-art denoising strategies. Results demonstrate significant SNR improvements when using our proposed approach when compared to other approaches.ConclusionsA new reconstruction method based on a noise-compensated homotopic modified James-Stein non-local regularized optimization strategy was developed for the purpose of improving the quality of rapid OCT image acquisitions. Preliminary results show the proposed method shows considerable promise as a tool to improve the visualization and analysis of biological material using OCT.

Multi-penalty conditional random field approach to super-resolved reconstruction of optical coherence tomography images

Improving the spatial resolution of Optical Coherence Tomography (OCT) images is important for the visualization and analysis of small morphological features in biological tissue such as blood vessels, membranes, cellular layers, etc. In this paper, we propose a novel reconstruction approach to obtaining super-resolved OCT tomograms from multiple lower resolution images. The proposed Multi-Penalty Conditional Random Field (MPCRF) method combines four different penalty factors (spatial proximity, first and second order intensity variations, as well as a spline-based smoothness of fit) into the prior model within a Maximum A Posteriori (MAP) estimation framework. Test carried out in retinal OCT images illustrate the effectiveness of the proposed MPCRF reconstruction approach in terms of spatial resolution enhancement, as compared to previously published super resolved image reconstruction methods. Visual assessment of the MPCRF results demonstrate the potential of this method in better preservation of fine details and structures of the imaged sample, as well as retaining the sharpness of biological tissue boundaries while reducing the effects of speckle noise inherent to OCT. Quantitative evaluation using imaging metrics such as Signal-to-Noise Ratio (SNR), Contrast to Noise Ratio (CNR), Equivalent Number of Looks (ENL), and Edge Preservation Parameter show significant visual quality improvement with the MPCRF approach. Therefore, the proposed MPCRF reconstruction approach is an effective tool for enhancing the spatial resolution of OCT images without the necessity for significant imaging hardware modifications.

3D assessment of void and gap formation in flowable resin composites using optical coherence tomography.

To investigate the effect of composite type and cavity size on gap and void formation using optical coherence tomography (OCT). Class I cavities of two depths (2 mm or 4 mm; 4 mm diameter) were prepared, treated with Tri-S Bond (Kuraray Medical), and bulk filled with either Surefil SDR Flow (SF; Dentsply) or Clearfil Majesty LV (MJ; Kuraray Medical) to form four groups. After 24 h, the specimens were 3D scanned using swept-source OCT (Santec) with 1310 nm laser at a 20 kHz sweep rate. In OCT tomograms, the bonding interface and the bulk of the restorations were evaluated. The percentage values of sealed interfaces (SP) and void volume (VP) for all groups were calculated and statistically analyzed using two- and one-way ANOVA and Tukey's post-hoc test. Selected specimens were cross sectioned and observed using a scanning electron microscope (SEM) and a confocal laser scanning microscope to confirm OCT findings. The following values were obtained for SP and VP, respectively: SF-2mm: 92% and 0.08%; SF-4mm: 66% and 0.13%; MJ-2mm: 86% and 1.79%; MJ-4mm: 33% and 1.96%. Both composites showed a significant increase in gap formation at 4-mm cavity depth (p < 0.001). While SF showed a rather homogeneous bulk compared to MJ, cavity depth did not significantly affect the void volume fraction (p = 0.08). The flowable composite with SDR (stress-decreasing resin) technology performed better than the conventional composite; however, bulk filling a 4-mm-deep cavity will compromise the sealing of the bonding interface regardless of the type of composite. OCT is a unique method of characterizing materials and their behaviors nondestructively and precisely.

Tensor total variation approach to optical coherence tomography reconstruction for improved visualization of retinal microvasculature

A novel optical coherence tomography (OCT) reconstruction approach is introduced for improved visualization of inner-retina capillaries in retinal OCT tomograms. The proposed method utilizes a minimization framework based on a tensor total variation (TTV) energy functional, to enforce capillary structural characteristics in the spatial domain. By accounting for structure tensor characteristics, the TTV reconstruction method allows for contrast enhancement of capillary structural characteristics. The novel TTV method was tested on high resolution OCT images acquired in-vivo from the foveal region of the retina of a healthy human subject. Experimental results demonstrate significant contrast and visibility enhancement of the inner retina capillaries in the retinal OCT tomograms, achieved by use of the TTV reconstruction method. Therefore, the TTV method has a strong potential for improved disease progression analysis based on the study of disease-induced changes in the inner retina vasculature.

Optical Coherence Tomography: its role in the non-invasive structural examination and conservation of cultural heritage objects—a review

A brief introduction to Optical Coherence Tomography (OCT) is presented, stressing the origin of the tomographic signal and the detection methods defining various modalities of the technique. The parameters of the tomographs, such as axial and lateral resolution, wavelength and intensity of the probing light, imaging range, time of examination, and sensitivity are then defined, and a paradigm for interpreting the OCT tomograms provided. The second part of the article comprises a review of the utilisation of OCT for structural examination of artworks, illustrated with some representative results. Applications to the structural imaging of semi-transparent subsurface layers such as varnishes and glazes, of underdrawings and of reverse painting on glass, are described first, and then applications in the examination of the structure and state of preservation of historic glass, jade, glazed porcelain and faience are discussed. Finally, the use of OCT combined with LIBS analysis and laser ablation of surface layers is presented.

Structural Examination of Easel Paintings with Optical Coherence Tomography

Identification of the order, thickness, composition, and possibly the origin of the paint layers forming the structure of a painting, that is, its stratigraphy, is important in confirming its attribution and history as well as planning conservation treatments. The most common method of examination is analysis of a sample collected from the art object, both visually with a microscope and instrumentally through a variety of sophisticated, modern analytical tools. Because of its invasiveness, however, sampling is less than ideally compatible with conservation ethics; it is severely restricted with respect to the amount of material extirpated from the artwork. Sampling is also rather limited in that it provides only very local information. There is, therefore, a great need for a noninvasive method with sufficient in-depth resolution for resolving the stratigraphy of works of art. Optical coherence tomography (OCT) is a noninvasive, noncontact method of optical sectioning of partially transparent objects, with micrometer-level axial resolution. The method utilizes near-infrared light of low intensity (a few milliwatts) to obtain cross-sectional images of various objects; it has been mostly used in medical diagnostics. Through the serial collection of many such images, volume information may be extracted. The application of OCT to the examination of art objects has been in development since 2003. In this Account, we present a short introduction to the technique, briefly discuss the apparatus we use, and provide a paradigm for reading OCT tomograms. Unlike the majority of papers published previously, this Account focuses on one, very specific, use of OCT. We then consider two examples of successful, practical application of the technique. At the request of a conservation studio, the characteristics of inscriptions on two oil paintings, originating from the 18th and 19th centuries, were analyzed. In the first case, it was possible to resolve some questions concerning the history of the work. From an analysis of the positions of the paint layers involved in three inscriptions in relation to other strata of the painting, the order of events in its history was resolved. It was evident that the original text had been overpainted and that the other inscriptions were added later, thus providing convincing evidence as to the painting's true date of creation. In the second example, a painting was analyzed with the aim of confirming the possibility of forgery of the artist's signature, and evidence strongly supporting this supposition is presented. These two specific examples of successful use of the technique on paintings further demonstrate how OCT may be readily adaptable to other similar tasks, such as in the fields of forensic or materials science. In a synergistic approach, in which information is obtained with a variety of noninvasive techniques, OCT is demonstrably effective and offers great potential for further development.

Interval type-II fuzzy anisotropic diffusion algorithm for speckle noise reduction in optical coherence tomography images

A novel speckle noise reduction algorithm based on a combination of Anisotropic Diffusion (AD) filtering and Interval Type-II fuzzy system was developed for reducing speckle noise in Optical Coherence Tomography (OCT) images. Unlike regular AD, the Interval Type-II fuzzy based AD algorithm considers the uncertainty in the calculated diffusion coefficient and appropriate adjustments to the coefficient are made. The new algorithm offers flexibility in optimizing the trade-off between the two image metrics: signal-to-noise (SNR) and Edginess, which are directly related to the structure of the imaged object. Application of the Interval Type-II fuzzy AD algorithm to OCT tomograms acquired in-vivo from a human finger tip and human retina show reduction in the speckle noise with very little edge blurring and about 13 dB and 7 dB image SNR improvement respectively. Comparison with Wiener, Adaptive Lee and regular Anisotropic Diffusion filters, applied to the same images, demonstrates the superior performance of the fuzzy Type-II AD algorithm in terms image SNR and edge preservation metrics improvement.

Optical coherence tomography in art diagnostics and restoration

An overview of the technique of optical coherence tomography (OCT) is presented, and a spectral OCT instrument especially designed for art diagnostics is described. The applicability of OCT to the stratigraphy of oil paintings is discussed with emphasis on examination of the artist’s signature. For the first time, OCT tomograms of stained glass are presented and discussed. The utilisation of Spectral OCT in real-time monitoring of varnish ablation is discussed with examples of ablation, melting and evaporation, and exfoliation of the varnish layer provided, for the first time.

Influence of ocular chromatic aberration and pupil size on transverse resolution in ophthalmic adaptive optics optical coherence tomography

Optical coherence tomography (OCT) enables visualization of the living human retina with unprecedented high axial resolution. The transverse resolution of existing OCT approaches is relatively modest as compared to other retinal imaging techniques. In this context, the use of adaptive optics (AO) to correct for ocular aberrations in combination with OCT has recently been demonstrated to notably increase the transverse resolution of the retinal OCT tomograms. AO is required when imaging is performed through moderate and large pupil sizes. A fundamental difference of OCT as compared to other imaging techniques is the demand of polychromatic light to accomplish high axial resolution. In ophthalmic OCT applications, the performance is therefore also limited by ocular chromatic aberrations. In the current work, the effects of chromatic and monochromatic ocular aberrations on the quality of retinal OCT tomograms, especially concerning transverse resolution, sensitivity and contrast, are theoretically studied and characterized. The repercussion of the chosen spectral bandwidth and pupil size on the final transverse resolution of OCT tomograms is quantitatively examined. It is found that losses in the intensity of OCT images obtained with monochromatic aberration correction can be up to 80 %, using a pupil size of 8 mm diameter in combination with a spectral bandwidth of 120 nm full width at half maximum for AO ultrahigh resolution OCT. The limits to the performance of AO for correction of monochromatic aberrations in OCT are established. The reduction of the detected signal and the resulting transverse resolution caused by chromatic aberration of the human eye is found to be strongly dependent on the employed bandwidth and pupil size. Comparison of theoretical results with experimental findings obtained in living human eyes is also provided.

Ultrahigh-resolution optical coherence tomography.

In the past two decades, optical coherence tomography (OCT) has been established as an adjunct diagnostic technique for noninvasive, high-resolution, cross-sectional imaging in a variety of medical fields. The rapid development of ultrabroad bandwidth light sources has recently enabled a significant improvement in OCT imaging resolution, demonstrating the potential of OCT to accomplish its original goal of performing noninvasive optical biopsies, i.e., the in vivo visualization of microstructural morphology in situ, which had previously only been possible with histopathology. In addition, these novel light sources might also enable the use of spectroscopic OCT, an extension of ultrahigh-resolution OCT, for enhancing image contrast as well as detecting spatially resolved functional, biochemical tissue information. State-of-the-art-light sources that now permit ultrahigh-resolution OCT covering the whole wavelength region from 500 to 1600 nm are reviewed and fundamental limitations of OCT image resolution are discussed. Ex vivo ultrahigh-resolution OCT tomograms are compared with histological results; first clinical in vivo ultrahigh-resolution OCT and preliminary spectroscopic OCT results are presented and their impact for future clinical and research applications is discussed.

Histologic correlation of pig retina radial stratification with ultrahigh-resolution optical coherence tomography.

To compare ultrahigh-resolution optical coherence tomography (OCT) cross-sectional images of the pig retina with histology, to evaluate the potential of ultrahigh-resolution OCT for enhanced visualization of intra- and subretinal structures. Ultrahigh-resolution OCT images were acquired with 1.4- micro m axial x 3- micro m transverse resolution from in vitro posterior eyecup preparations of the domestic pig. Frozen sections were obtained in precise alignment with OCT tomograms, by using major blood vessels as orientation markers and were counterstained with cresyl violet or unstained and examined by differential interference contrast microscopy. Micrographs from histologic sections were linearly scaled to correct for tissue shrinkage and compared with OCT tomograms. In the proximal retina, ultrahigh-resolution OCT signal bands directly corresponded to the main retinal layers. For the wavelength region used ( approximately 800 nm), axodendritic layers (nerve fiber layer, inner and outer plexiform layers) were more reflective than cell body layers (ganglion cell layer, inner nuclear layer, outer nuclear layer). In the distal retina, substructures of the photoreceptor layer such as the interface between inner and outer segments were visualized, and the retinal pigment epithelium, the choriocapillaris, and superficial choroid layers were resolved. In addition, the time sequence of a retinal detachment event was monitored by ultrahigh-resolution OCT. In vitro ophthalmic ultrahigh-resolution OCT imaging reveals retinal morphology with unprecedented detail. The specific assignment of OCT signal patterns to retinal substructures provides a basis for improved interpretation of in vivo ophthalmic OCT tomograms of high clinical relevance.

Optical coherence tomography findings in adult-onset foveomacular vitelliform dystrophy

PURPOSE: The purpose of this article is to analyze cross-sectional images of a subretinal macular lesion, using optical coherence tomography (OCT) in eyes with adult-onset foveomacular vitelliform dystrophy (AOFVD), to compare thickness of the neurosensory retina over the lesion with best-corrected visual acuity (BCVA) of each eye, and to compare OCT tomograms of AOFVD patients with OCT of Best disease. DESIGN: Observational case series. METHODS: This is a retrospective study which took place in a clinical practice. Forty-three patients (72 eyes) with AOFVD and 12 patients (24 eyes) with Best’s disease were studied. The observation procedures used were biomicroscopic fundus examination, fluorescein angiography (FA), indocyanine green angiography (ICGA), and optical coherence tomography (OCT). The main outcome measures were a description of the typical picture of AOFVD in OCT tomograms, the relationship between the neurosensory retinal thickness over the lesion, the BCVA expressed in decimal terms, and a comparison with description of OCT in Best disease. RESULTS: Of the 43 patients affected by AOFVD, 29 had bilateral macular lesions. Fluorescein angiography showed a central hypofluorescent spot surrounded by an irregular hyperfluorescent ring in 65 of the 72 eyes. Indocyanine green angiography demonstrated a central nonfluorescent spot and a hyperfluorescent area surrounding the central spot in 22 of 27 eyes examined. In all 72 eyes of 43 patients, OCT showed a well-defined central region of thickening in the reflective band representing the retinal pigment epithelium (RPE). The relationship between the thickness of neurosensory retina over the lesion and BCVA was significant ( P = .001, r 2 = 0.61). Optical coherence tomography in all 24 eyes with Best disease showed a well-defined central serous retinal detachment. CONCLUSION: In the 72 eyes with AOFVD, FA and ICGA presented different features. Instead, OCT tomograms showed a well-defined subretinal thickening of the RPE in all the eyes. The lack of difference in OCT patterns between cases with or without the hypofluorescent spot on angiography was useful for confirming the diagnosis of AOFVD. Moreover, a reduced visual acuity was evident in patients with a thinner neurosensory retinal layer over AOFVD lesion. Finally, OCT images were also useful for distinguishing AOFVD from Best disease.

The macular thickness and volume in glaucoma: an analysis in normal and glaucomatous eyes using OCT

To evaluate macular volume in normal and glaucomatous eyes using Optical Coherence Tomography (OCT). Fifty eyes of 30 patients (age: 49-68); 20 eyes normal, 15 eyes with early glaucoma and 15 eyes with advanced glaucoma have been studied with the commercially available OCT unit (OCT 2000) (Humphrey Zeiss, Dublin, CA, USA). All eyes were examined at a scan length of 3.44 mm vertically across the fovea. OCT macular retinal thickness maps were used to calculate macular volume. We observed significant differences between groups. Normals (7.35 +/- 0.455 mm3) and early glaucoma (7.09 +/- 0.475 mm3), each had significantly greater volume than subjects with advanced glaucoma (6.678 +/- 0.455 mm3). Volumetric analysis of macular thickness with OCT tomograms may be a useful method of documenting and monitoring patients with early glaucoma and advanced glaucoma. In our analysis, and according to the observations of other authors, OCT macular volumes correlates significantly with glaucoma status.

In vivo detection of experimentally induced cortical dysgenesis in the adult rat neocortex using optical coherence tomography

Imaging cerebral structure in vivo can be accomplished by many methods, including MRI, ultrasound, and computed tomography. Each offers advantages and disadvantages with respect to the others, but all are limited in spatial resolution to millimeter-scale features when used in routine applications. Optical coherence tomography (OCT) is a new, high resolution imaging technique which uses light to directly image living tissue. Here, we investigate the potential use of OCT for structural imaging of the fully developed mammalian cerebral cortex. In particular, we show that OCT can perform in vivo detection of neocortex and differentiate normal and abnormal cortical anatomy. We present the results of detailed optical coherence tomographic (OCT) observations of both normal and abnormal rat neocortex obtained in vivo. Comparative histologic analysis shows excellent correlation with the OCT tomograms.