Capability Of Optical Coherence Tomography Research Articles

Full field measurements and identification in Solid Mechanics Depth-resolved Phase Imaging

Traditional full-field interferometric techniques (speckle, moiré, holography etc) encode the surface deformation state of the object under test in the form of 2-D phase images. Over the past 10 years, a family of related techniques (Wavelength Scanning Interferometry, Phase Contrast Spectral Optical Coherence Tomography (OCT), Tilt Scanning Interferometry and Hyperspectral Interferometry) has emerged that allows one to measure the volume deformation state within weakly-scattering objects. The techniques can be thought of as combining the phase-sensing capabilities of Phase Shifting Interferometry and the depth-sensing capabilities of OCT. This paper provides an overview of the techniques, and describes a theoretical framework based on the Ewald sphere construction that allows key parameters such as depth resolution and displacement sensitivity to be calculated straightforwardly for any given optical geometry and wavelength scan range. Finally, the related issue of robust phase unwrapping of noisy 3-D wrapped phase volumes is also described.

Use of optical coherence tomography in the diagnosis and management of uveitis.

Regatieri, Caio V. MD, PhD; Alwassia, Ahmad MD; Zhang, Jason Y. MD; Vora, Robin MD; Duker, Jay S. MD Author Information

Optical coherence tomography (OCT) findings in patients with optic tract syndrome

Purpose To analyze retinal nerve fiber layer (RNFL) thickness in eyes with optic tract syndrome (OTS) by using optical coherence tomography (OCT) and to evaluate the capability of OCT to detect the characteristic pattern of RNFL loss. Methods Eight patients (4 males and 4 females) with optic tract syndrome were enrolled in this retrospective collection of medical records. Characteristics including age, sex, etiology of optic tract lesion, visual acuity, visual field defect type were recorded. The diagnosis of optic tract syndrome were made by clinical history and typical optic disc findings, visual field defect and neuro-imaging findings including brain MRI and/or CT. The average of RNFL thickness of optic disc, four quadrants, specific four o’clock meridians and related parameters were analyzed and compared between both eyes. Results The nasal segment average of RNFL thickness was significantly lower in contralateral eyes than that of ipsilateral eyes (37.5 ± 6.7 μm and 67.9 ± 10.3 μm respectively; p < 0.001). The average RNFL thickness and mean thickness of other three quadrants were not significantly different between both eyes. The ratio of superior maximum to nasal segment (Smax/Navg), superior maximum to temporal segment (Smax/Tavg) and inferior maximum to temporal segment (Imax/Tavg) of were significantly different between both eyes ( p < 0.001 in all comparisons). The RNFL thickness at nasal, temporal sectors of the contralateral and those at superior, inferior sectors of the ipsilateral eyes were significantly thinner than those of fellow eyes. Conclusion The RNFL thickness measured by OCT demonstrated a characteristic pattern of optic atrophies in OTS. The difference of nasal average, Smax/Navg, Smax/Tavg, Imax/Tavg values and specific radians between both eyes can provide useful information in the diagnosis of optic tract syndrome.

Optical Coherence Tomography in the Diagnosis and Management of Diabetic Macular Edema: Time-Domain Versus Spectral-Domain

Optical coherence tomography (OCT) is an important imaging modality in the setting of diabetic macular edema (DME). Its use allows more precise evaluation of retinal pathology in DME, including retinal thickness and edema, vitreomacular interface abnormalities, subretinal fluid, and foveal microstructural changes. Additional advantages include its ability to quantitatively monitor response to treatment of DME by laser, intravitreal pharmacotherapies, and vitreoretinal surgery. OCT measurements are now used in all major clinical studies of DME treatment as critical endpoints. This article presents a review of both time-domain and spectral-domain OCT in the diagnosis and management of DME. The authors discuss the various parameters evaluated by the OCT systems and provide an evidence-based evaluation of their accuracy, significance, reliability, and limitations. As the capability of OCT continues to advance, it appears that its use will play an increasingly important role in the understanding, evaluation, and treatment of DME.

Adaptive optics and the eye (super resolution OCT)

The combination of adaptive optics (AO) and optical coherence tomography (OCT) was first reported 8 years ago and has undergone tremendous technological advances since then. The technical benefits of adding AO to OCT (increased lateral resolution, smaller speckle, and enhanced sensitivity) increase the imaging capability of OCT in ways that make it well suited for three-dimensional (3D) cellular imaging in the retina. Today, AO-OCT systems provide ultrahigh 3D resolution (3 × 3 × 3 μm³) and ultrahigh speed (up to an order of magnitude faster than commercial OCT). AO-OCT systems have been used to capture volume images of retinal structures, previously only visible with histology, and are being used for studying clinical conditions. Here, we present representative examples of cellular structures that can be visualized with AO-OCT. We overview three studies from our laboratory that used ultrahigh-resolution AO-OCT to measure the cross-sectional profiles of individual bundles in the retinal nerve fiber layer; the diameters of foveal capillaries that define the terminal rim of the foveal avascular zone; and the spacing and length of individual cone photoreceptor outer segments as close as 0.5° from the fovea center.

Trend-Based Analysis of Retinal Nerve Fiber Layer Thickness Measured by Optical Coherence Tomography in Eyes with Localized Nerve Fiber Layer Defects

To evaluate the rate of change in retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) in eyes with stable and progressive localized RNFL defects and to investigate, in a trend-based approach, the diagnostic capability of OCT in the detection of progressive RNFL thinning. The study included 153 glaucomatous eyes with localized RNFL defects. The patients were divided into nonprogressors (n = 77) and progressors (n = 76) on the basis of an evaluation of serial red-free photographs. The rates of progressive thinning in global, quadrant, and clock-hour OCT RNFL thicknesses were determined, by linear regression, and were compared between groups. Areas under receiver operating characteristic curves and sensitivities at fixed specificities were calculated for each parameter. The rate of progressive RNFL thinning was significantly faster in progressors than in nonprogressors globally; in the inferior quadrant; in the 10, 11, 6, and 7 o'clock sectors; and in the affected quadrant and clock-hour sector thicknesses (all P ≤ 0.001). The rate of RNFL thinning in affected clock-hour sectors had the highest ability to discriminate between stable and progressive RNFL thinning with a sensitivity of 62% (95% confidence interval, 50%-73%) at a specificity ≥80%. Agreement between OCT and red-free photography was strongest when the criterion of -3.6 μm/year with P < 0.1 was used for each clock hour. The rate of OCT RNFL thinning was significantly greater in patients with progressive localized RNFL defects than in those with stable localized defects. The data suggest that trend-based analysis of OCT RNFL thickness may be useful in glaucoma progression analysis and may complement other diagnostic tests.

Integrated Optical Coherence Tomography and Microscopy for Ex Vivo Multiscale Evaluation of Human Breast Tissues

Three-dimensional (3D) tissue imaging methods are expected to improve surgical management of cancer. In this study, we examined the feasibility of two 3D imaging technologies, optical coherence tomography (OCT) and optical coherence microscopy (OCM), to view human breast specimens based on intrinsic optical contrast. Specifically, we imaged 44 ex vivo breast specimens including 34 benign and 10 malignant lesions with an integrated OCT and OCM system developed in our laboratory. The system enabled 4-μm axial resolution (OCT and OCM) with 14-μm (OCT) and 2-μm (OCM) transverse resolutions, respectively. OCT and OCM images were compared with corresponding histologic sections to identify characteristic features from benign and malignant breast lesions at multiple resolution scales. OCT and OCM provide complimentary information about tissue microstructure, thus showing distinctive patterns for adipose tissue, fibrous stroma, breast lobules and ducts, cysts and microcysts, as well as in situ and invasive carcinomas. The 3D imaging capability of OCT and OCM provided complementary information to individual 2D images, thereby allowing tracking features from different levels to identify low-contrast structures that were difficult to appreciate from single images alone. Our results lay the foundation for future in vivo optical evaluation of breast tissues, using OCT and OCM, which has the potential to guide core needle biopsies, assess surgical margins, and evaluate nodal involvement in breast cancer.

Depth-resolved Imaging and Displacement Measurement Techniques Viewed as Linear Filtering Operations

The last 5 years have seen the emergence of a family of optical interferometric techniques that provide deformation measurements throughout three-dimensional (3-D) weakly scattering materials. They include wavelength scanning interferometry (WSI), tilt scanning interferometry (TSI), phase contrast spectral optical coherence tomography (PC SOCT) and hyperspectral interferometry (HSI) and can be thought of as a marriage between the phase sensing capabilities of Phase Shifting Interferometry and the depth-sensing capabilities of Optical Coherence Tomography. It was recently shown that some closely related 3-D optical imaging techniques can be treated as shift-invariant linear filtering operations. In this paper, we extend that work to include WSI, TSI, PC SOCT and HSI as spatial filtering operations and also relate the properties of their transfer functions in the spatial frequency domain to their spatial resolution and phase sensitivity, for depth-resolved displacement measurements.

Imaging of Human Lymph Nodes Using Optical Coherence Tomography: Potential for Staging Cancer

Histologic assessment is the gold standard technique for the identification of metastatic involvement of lymph nodes in malignant disease, but can only be performed ex vivo and often results in the unnecessary excision of healthy lymph nodes, leading to complications such as lymphedema. Optical coherence tomography (OCT) is a high-resolution, near-IR imaging modality capable of visualizing microscopic features within tissue. OCT has the potential to provide in vivo assessment of tissue involvement by cancer. In this morphologic study, we show the capability of OCT to image nodal microarchitecture through an assessment of fresh, unstained ex vivo lymph node samples. Examples include both benign human axillary lymph nodes and nodes containing metastatic breast carcinoma. Through accurate correlation with the histologic gold standard, OCT is shown to enable differentiation of lymph node tissue from surrounding adipose tissue, reveal nodal structures such as germinal centers and intranodal vessels, and show both diffuse and well circumscribed patterns of metastatic node involvement.

Multispectral in vivo three-dimensional optical coherence tomography of human skin

The capability of optical coherence tomography (OCT) to perform "optical biopsy" of tissues within a depth range of 1 to 2 mm with micron-scale resolution in real time makes it a promising biomedical imaging modality for dermatologic applications. Three high-speed, spectrometer-based frequency-domain OCT systems operating at 800 nm (20,000 A-scans/s), 1060 nm, and 1300 nm (both 47,000 A-scans/s) at comparable signal-to-noise ratio (SNR), SNR roll-off with scanning depth, and transverse resolution (<15 microm) were used to acquire 3-D tomograms of glabrous and hairy human skin in vivo. Images obtained using these three systems were compared in terms of penetration depth, resolution, and contrast. Normal as well as abnormal sites like moles and scar tissue were examined. In this preliminary study, skin pigmentation had little effect on penetration accomplished at three different wavelengths. The epidermis and dermal-epidermal junction could be properly delineated using OCT at 800 nm, and this wavelength offered better contrast over the other two wavelength regions. OCT at 1300 nm permits imaging of deeper dermal layers, critical for detecting deeper tumor boundaries and other deeper skin pathologies. The performance at 1060 nm compromises between the other wavelengths in terms of penetration depth and image contrast.

LIVE IMAGING OF EARLY DEVELOPMENTAL PROCESSES IN MAMMALIAN EMBRYOS WITH OPTICAL COHERENCE TOMOGRAPHY

Early embryonic imaging of cardiovascular development in mammalian models requires a method that can penetrate through and distinguish the many tissue layers with high spatial and temporal resolution. In this paper we evaluate the capability of Optical Coherence Tomography (OCT) technique for structural 3D embryonic imaging in mouse embryos at different stages of the developmental process ranging from 7.5 dpc up to 10.5 dpc. Obtained results suggest that the collected data is suitable for quantitative and qualitative measurements to assess cardiovascular function in mouse models, which is likely to expand our knowledge of the complexity of the embryonic heart, and its development into an adult heart.

Application of hyperosmotic agent to determine gastric cancer with optical coherence tomography ex vivo in mice

Noninvasive tumor imaging could lead to the early detection and timely treatment of cancer. Optical coherence tomography (OCT) has been reported as an ideal diagnostic tool for distinguishing tumor tissues from normal tissues based on structural imaging. In this study, the capability of OCT for functional imaging of normal and tumor tissues based on time- and depth-resolved quantification of the permeability of biomolecules through these tissues is investigated. The orthotopic graft model of gastric cancer in nude mice is used, normal and tumor tissues from the gastric wall are imaged, and a diffusion of 20% aqueous solution of glucose in normal stomach tissues and gastric tumor tissues is monitored and quantified as a function of time and tissue depth by an OCT system. Our results show that the permeability coefficient is (0.94+/-0.04)x10(-5) cms in stomach tissues and (5.32+/-0.17)x10(-5) cms in tumor tissues, respectively, and that tumor tissues have a higher permeability coefficient compared to normal tissues in optical coherence tomographic images. From the results, it is found that the accurate and sensitive assessment of the permeability coefficients of normal and tumor tissues offers an effective OCT image method for detection of tumor tissues and clinical diagnosis.

Clinical and research applications of anterior segment optical coherence tomography – a review

Optical coherence tomography (OCT) is being employed more and more often to image pathologies and surgical anatomy within the anterior segment, specifically in anterior chamber biometry, corneal pachymetric mapping, angle evaluation and high-resolution cross-sectional imaging. The cross-sectional imaging capability of OCT is similar to ultrasound, but its higher resolution allows OCT to measure and visualize very fine anatomic structures. No contact is required. In this review, we describe the utility and limitations of anterior segment OCT.

Optical Coherence Tomography Imaging of the Inner Ear: A Feasibility Study with Implications for Cochlear Implantation

Cochlear implantation is now being performed in ears with residual hearing. Those implant recipients who keep residual hearing may benefit from improved pitch resolution through both electrical and acoustic hearing. Preservation of cochlear function after implantation is a challenging task for the surgeon. Current topics of hearing preservation research include electrode design and surgical technique. To maintain hearing, surgeons strive to create a cochleostomy and place the electrode in a minimally traumatic fashion. In this study, we examine a novel catheter-based real-time imaging modality with 10- to 15-microm resolution, optical coherence tomography (OCT), on the inner ear. We demonstrate the capability of OCT to allow visualization of inner ear structures through bone in live mice. We additionally used OCT to image the inner ear in a human temporal bone. Optical coherence tomography was able to delineate soft tissue structures within the cochlea and may be useful as an adjunct to cochlear implantation. Other potential otologic applications of OCT are discussed.

Optical approach for monitoring the periodontal ligament changes induced by orthodontic forces around maxillary anterior teeth of white rats

Structural variations of the periodontal ligament (PDL) induced by orthodontic forces have been evaluated by optical coherence tomography (OCT) and compared to images obtained by conventional radiography. Here, two specially designed orthodontic appliances were installed on the maxillary anterior teeth of white rats for applying different magnitudes of orthodontic forces. Constant distraction force magnitudes of 0, 5, 10, and 30 gf were given to four respective rats over a period of 5 days. At the end of the treatment period, the rats were sacrificed and the maxillaries were extracted for X-ray and OCT imaging. The PDL variations, proportional to the force magnitude, were clearly indicated in the OCT measurements. The OCT images further showed that the ligament was torn for a constant orthodontic force of 30 gf. These results support the clinical dental application of OCT for monitoring the ligament changes during orthodontic procedures. The real-time imaging capability of OCT, together with its high resolution, has the potential to help dentists with in vivo orthodontic treatments in human subjects as well.

Permeability of hyperosmotic agent in normal and atherosclerotic vascular tissues

Noninvasive cardiovascular imaging could lead to the early detection and timely treatment of complex atherosclerotic lesions responsible for major cardiovascular events. Recent investigations have suggested that optical coherence tomography (OCT) is an ideal diagnostic tool due to the high resolution this technology achieves in discriminating the different features of atherosclerotic lesions based on structural imaging. We explore the capability of OCT for functional imaging of normal and atherosclerotic aortic tissues based on time- and depth-resolved quantification of the permeability of biomolecules through these tissues. The permeability coefficient of 20% aqueous solution of glucose was found to be (6.80+/-0.18)x10(-6) cms in normal aortas and (2.69+/-0.42)x10(-5) cms in aortas with atherosclerotic disease. The results suggest that this new OCT functional imaging method-the assessment of the permeability coefficients of various physiologically neutral biomolecules in vascular tissues-could assist in early diagnosing and detecting the different components of atherosclerotic lesions.

Relationship between coronary remodeling and plaque characterization in patients without clinical evidence of coronary artery disease

AimsThe objectives of this study were: (1) to evaluate the relationship between coronary arterial remodeling assessed by intravascular ultrasound (IVUS) and plaque morphology assessed by histological examination in patients without clinical evidence of coronary artery disease and (2) to compare plaque morphology between histological examination and optical coherence tomography (OCT). MethodsCoronary segments (n=98) were harvested from the heart of 34 patients who died without clinical evidence of coronary artery disease. The segments with remodeling were assessed by IVUS and compared with corresponding OCT and histological images. ResultsThe fibrofatty plaque area was larger in lesions with expansive remodeling (ER) than in lesions with intermediate/constrictive remodeling (IR/CR) (p<0.01). Incidence of lipid containing plaque with the thickness of the fibrous cap smaller than 200μm tended to be higher in ER than in IR/CR (34% versus 13%, p=0.10). OCT assessment of lipid containing plaque with thinner fibrous cap was achieved with 92% sensitivity and 75% specificity. ConclusionsThe fibrofatty plaque area was larger in lesions with ER than IR/CR even in patients without clinical evidence of coronary artery disease. The current capabilities of OCT are well suited for evaluation of lipid containing plaques with thinner fibrous cap.

The role of optical coherence tomography in multiple sclerosis: Expert panel consensus

Optic neuritis (ON), a common manifestation of multiple sclerosis (MS), often occurs as the initial manifestation of central nervous system demyelination or develops during the course of this disease. Since the retinal nerve fiber layer (RNFL) is composed only of unmyelinated axons, measuring RNFL thickness represents a viable method of monitoring axonal loss in these patients. Optical coherence tomography (OCT) is a noninvasive, noncontact, accurate, and reproducible technique that quantitates the thickness of the peripapillary RNFL, fovea, and macula. Because of its potential role in defining axonal loss in ON and in assessing longitudinal changes in the RNFL before and after MS treatment, a multidisciplinary expert panel was charged with the following tasks: assess the current capabilities of OCT; review the current data about OCT, ON, and MS; and determine whether OCT could be a primary or secondary outcome measure in future MS clinical trials. The panel concluded that: [1] OCT is valid and reproducible; [2] OCT has yielded some important limited data concerning cross-sectional studies with ON and MS; [3] more studies are required to correlate OCT results with other measures of MS disease activity; [4] after correlation with these other measures and upon agreement of standardized technical and statistical methods, OCT may evolve into a important primary or secondary outcome metric for MS clinical trials and patient care.

Prediction Capability of Optical Coherence Tomography for Blood Glucose Concentration Monitoring

Optical coherence tomography (OCT) has been shown to be a promising optical approach to noninvasive monitoring of blood glucose concentration because of its capability of probing optical properties at different depths in tissue with high resolution. This article investigates the capability of OCT to predict changes in blood glucose concentration. We varied blood glucose concentration in the physiological range in three sets of experiments. In the first set, we investigated large variations of blood glucose concentration ( approximately 400 mg/dl) and used 2100 OCT A scans for signal averaging. In the second set, we varied blood glucose concentration by approximately 200 mg/dl and used 8400 A scans for signal averaging. In the third set, we improved OCT blood glucose monitoring by increasing and controlling skin temperature under the OCT probe. In this set of experiments we increased the glucose concentration by approximately 300 mg/dl and used 4200 A scans for averaging. The predicted glucose concentrations in the first two sets were lower than actual glucose concentration by 10-20% (the mean shift), while the heating and temperature control in the third set of experiments reduced the mean shift down to 1.5%. Therefore, the mean shift was reduced substantially by tissue heating and temperature control. However, it did not depend on the number of A scans to be averaged. In contrast, the uncertainty in OCT prediction of glucose concentration (the standard deviation) did not depend on heating and temperature control, but was reduced substantially from 56 to 24 mg/dl by increasing the number of A scans from 2100 to 8400, respectively. These results suggest that the accuracy of OCT-based glucose monitoring is approaching that of standard invasive and minimally invasive techniques.

Diagnostic Capability of Optical Coherence Tomography (Stratus OCT 3) in Early Glaucoma

To evaluate the diagnostic capability of optical coherence tomography (Stratus OCT 3) for early glaucoma in Asian Indian eyes. Cross-sectional observational study. Two groups of patients (early glaucoma and normal) who satisfied the inclusion and exclusion criteria were included. Early glaucoma was diagnosed in presence of open angles, characteristic glaucomatous optic disc changes correlating with the visual field on automated perimetry (visual field defect fulfilling at least 2 of Anderson and Patella's 3 criteria with mean deviation > or = -6 dB). Normals had visual acuity > or =20/30, intraocular pressure <22 mmHg with normal optic disc and fields and no ocular abnormality. All patients underwent complete ophthalmic evaluation including visual field examination (24-2/30-2 SITA standard program) and imaging with Stratus OCT 3. Sensitivity, specificity, positive and negative predictive values, area under the receiving operating characteristic curve and likelihood ratios were calculated for various Stratus OCT 3 parameters. Seventy-two eyes (72 patients) with early glaucoma and 96 eyes (96 normal subjects) were analyzed. The inferior maximum parameter had the best combination of sensitivity and specificity, 75% (95% confidence interval [CI], 70.2-79.8%) and 89.6% (95% CI, 82.6-96.6%), respectively. The 6-o'clock parameter had a sensitivity of 61.1% (95% CI, 52.3-69.9) and specificity of 99% (95% CI, 95-100); for an assumed prevalence of 5%, the positive and negative predictive values were 75% and 98%, respectively. The positive likelihood ratio for the 6-o'clock parameter (P<5%) in early glaucoma was 61. Optical coherence tomography has moderate sensitivity with high specificity for the diagnosis of early glaucoma and may have a potential role in screening.