Showing papers on "Optical coherence tomography published in 2015"
TL;DR: Optical coherence tomography (OCT) was introduced in the 1990s in dermatology and is nowadays established as a noninvasive high-resolution technique for the in vivo evaluation of the skin this paper.
Abstract: Optical coherence tomography (OCT) was introduced in the 1990s in dermatology and is nowadays established as a noninvasive high-resolution technique for the in vivo evaluation of the skin. To date several studies have been successfully demonstrated the application of OCT for various dermatological questions. The main indication for OCT in the daily practice is the noninvasive diagnosis of nonmelanoma skin cancer such as actinic keratosis and basal cell carcinoma. OCT has also been shown to be a valuable tool in treatment monitoring and evaluation of therapeutic success of noninvasive treatment strategies like topical immune modulators or photodynamic treatment. Other potential applications for OCT include inflammatory diseases, microbial or parasitic infestations of the skin, e.g. scabies mites or onychomycosis. In recent years high-definition OCT devices have been developed that can potentially be used for the evaluation of melanocytic lesions and, due to the higher resolution, for the visualization of intrafollicular demodex mites. Furthermore different commercially available devices offer-in addition to the cross-sectional images-a fast-generated horizontal (en face) imaging mode. With respect to resolution and penetration depth the OCT technique is taking a middle position in comparison to other noninvasive imaging devices in dermatology such as sonography and reflectance confocal microscopy.
1,047 citations
TL;DR: Because of the quantity of data available and the potential for artifacts, physician interaction in viewing the image data will be required, much like what happens in modern radiology practice.
Abstract: Purpose:To describe image artifacts of optical coherence tomography (OCT) angiography and their underlying causative mechanisms. To establish a common vocabulary for the artifacts observed.Methods:The methods by which OCT angiography images are acquired, generated, and displayed are reviewed as are
777 citations
01 Nov 2015
TL;DR: In this paper, the authors describe image artifacts of OCT angiography and their underlying causative mechanisms, and establish a common vocabulary for the artifacts observed, and provide a review of the methods by which OCT images are acquired, generated and displayed.
Abstract: Purpose:To describe image artifacts of optical coherence tomography (OCT) angiography and their underlying causative mechanisms. To establish a common vocabulary for the artifacts observed.Methods:The methods by which OCT angiography images are acquired, generated, and displayed are reviewed as are
589 citations
TL;DR: The purpose of this review is to help readers understand and select appropriate OCT angiography algorithm for use in specific applications and it is found that the method that utilizes complex OCT signal to contrast retinal blood flow delivers the best performance among all the algorithms in terms of image contrast and vessel connectivity.
Abstract: Optical coherence tomography (OCT)-based angiography is increasingly becoming a clinically useful and important imaging technique due to its ability to provide volumetric microvascular networks innervating tissue beds in vivo without a need for exogenous contrast agent. Numerous OCT angiography algorithms have recently been proposed for the purpose of contrasting microvascular networks. A general literature review is provided on the recent progress of OCT angiography methods and algorithms. The basic physics and mathematics behind each method together with its contrast mechanism are described. Potential directions for future technical development of OCT based angiography is then briefly discussed. Finally, by the use of clinical data captured from normal and pathological subjects, the imaging performance of vascular networks delivered by the most recently reported algorithms is evaluated and compared, including optical microangiography, speckle variance,phase variance, split-spectrum amplitude decorrelation angiography, and correlation mapping. It is found that the method that utilizes complex OCT signal to contrast retinal blood flow delivers the best performance among all the algorithms in terms of image contrast and vessel connectivity. The purpose of this review is to help readers understand and select appropriate OCT angiography algorithm for use in specific applications.
312 citations
TL;DR: Optical coherence tomography angiography provides a noninvasive method to visualize and measure the superficial and deep plexus FAZ in a normal population, which can vary in size and shape, with the FAZ area significantly larger in the deep compared with the superficial plexi.
Abstract: Purpose:To analyze the foveal avascular zone (FAZ) in normal eyes using optical coherence tomography angiography.Methods:Prospective noncomparative case series. The parafoveal region of 70 eyes from 67 healthy subjects was imaged using optical coherence tomography angiography to visualize the superf
290 citations
TL;DR: To the best of the knowledge, this is the first validated, fully-automated, seven-layer and fluid segmentation method which has been applied to real-world images containing severe DME.
Abstract: We present a fully automatic algorithm to identify fluid-filled regions and seven retinal layers on spectral domain optical coherence tomography images of eyes with diabetic macular edema (DME). To achieve this, we developed a kernel regression (KR)-based classification method to estimate fluid and retinal layer positions. We then used these classification estimates as a guide to more accurately segment the retinal layer boundaries using our previously described graph theory and dynamic programming (GTDP) framework. We validated our algorithm on 110 B-scans from ten patients with severe DME pathology, showing an overall mean Dice coefficient of 0.78 when comparing our KR + GTDP algorithm to an expert grader. This is comparable to the inter-observer Dice coefficient of 0.79. The entire data set is available online, including our automatic and manual segmentation results. To the best of our knowledge, this is the first validated, fully-automated, seven-layer and fluid segmentation method which has been applied to real-world images containing severe DME.
275 citations
TL;DR: Although fluorescein angiography remains the gold standard for determining the presence of leakage, and OCT shows fluid accumulation and its variations, OCTA may now offer noninvasive monitoring of the CNV, aiding for each treatment decision during the follow-up.
Abstract: Purpose:To compare optical coherence tomography angiography (OCTA) with traditional multimodal imaging in patients with exudative age-related macular degeneration in terms of guiding the treatment decision.Methods:Prospective case series of 80 eyes of 73 consecutive patients with exudative age-relat
267 citations
TL;DR: In this article, a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation is presented, where a lead zirconate titanate stack actuator is employed to achieve the sinusoid vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays.
Abstract: We present a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation. For the sinusoidal modulation strategy, a lead zirconate titanate stack actuator is employed to achieve the sinusoidal vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays. The purpose of this strategy is to get higher performance complex-conjugate artifact elimination. Bessel separation of the signal sequence at each wavelength of the spectrometer was used to reconstruct the real and imaginary components of interference fringes; however, the sinusoidal modulation method is independent of light source wavelength. The experimental results demonstrated that the method had an excellent performance in a complex-conjugate suppression of 50 dB for a full width at half maximum bandwidth of 236 nm, and it has better anti-artifact ability and more flexible range in phase shifting than the conventional wavelength-dependent phase-shifting method on a full-range complex spectral optical coherence tomography system. Furthermore, the effect of the hysteresis error of lead zirconate titanate actuators on the performance of complex-conjugate artifact elimination was investigated and the solution of lead zirconate titanate positioning performance for both conventional phase-shifting and sine-modulation methods was suggested.
260 citations
TL;DR: The description of the mechanical contrast that has been employed by OCE is described and the state-of-the-art techniques based on the reported applications are reviewed and the current technical challenges are discussed, emphasizing the unique role of OCE in tissue mechanical characterization.
Abstract: The position of OCE among other elastography techniques.
Optical coherence elastography (OCE) represents the frontier of optical elasticity imaging techniques and focuses on the micro-scale assessment of tissue biomechanics in 3D that is hard to achieve with traditional elastographic methods. Benefit from the advancement of optical coherence tomography, and driven by the increasing requirements in nondestructive biomechanical characterization, this emerging technique recently has experienced a rapid development. In this paper, we start with the description of the mechanical contrast that has been employed by OCE and review the state-of-the-art techniques based on the reported applications and discuss the current technical challenges, emphasizing the unique role of OCE in tissue mechanical characterization.
249 citations
TL;DR: Optical coherence tomography angiography can separately detect the superficial vascular and the deep vascular networks in the inner retina, which are overlaid and seem to be fused when seen with standard angiographies.
Abstract: Purpose:To evaluate retinal vessel morphology using split-spectrum amplitude-decorrelation angiography with optical coherence tomography in healthy eyes.Methods:Fifty-two eyes of 26 healthy volunteers (age range from 35 to 48 years; mean age 41.94 years; SD: ±4.13) were evaluated by optical coherenc
239 citations
TL;DR: In healthy Chinese eyes, macular perfusion decreased with increasing age, and decreased more rapidly in males than in females, while the CFZ area was larger in females than in males, while all three parameters seemed to change more rapidly with age in malesthan in females.
Abstract: The retinal vascular system, especially the part that perfuses the macular area, is essential to normal visual function1 Numerous factors (eg, pathology, trauma) can cause severe and irreversible visual damage to the macula1,2 Ophthalmologists have used a variety of different methods to observe the vasculature in the macular area, including fundus camera3 and fundus fluorescein angiography (FFA)4 While these methods provide important clinical information, their use in clinical settings is limited by their invasive nature or low resolution Moreover, the monitoring of early and subtle changes in the macular capillary system in clinical settings has proven challenging Thus, an effective and noninvasive method for monitoring macular perfusion would provide not only a means for early detection of changes related to various pathologies, leading in turn to early interventions, but also a more thorough understanding of the pathophysiology of macular vascular disease
Recently, development of a new technique known as split-spectrum amplitude-decorrelation angiography (SSADA) has promised new insights for understanding ocular perfusion The technique, based on optical coherence tomography (OCT), is able to rapidly and accurately quantify retinal and disc blood flow in a noninvasive manner5,6 Previous research has demonstrated that OCT angiography (angio-OCT) with SSADA offers results with high intravisit repeatability and intervisit reproducibility7,8 However, an understanding of the status in normal eyes is necessary before its application in clinical settings Moreover, some previous studies have found that the thicknesses of the retinal nerve fiber layer (RNFL), the macula, and the choroid vary with both age and sex9–13 Thus, we here report on macular perfusion in normal volunteer subjects to explore the potential effects of age and sex on macular retinal functions
TL;DR: The diagnostic accuracy of OCT for detecting DMO and CSMO is determined in patients referred to ophthalmologists after DR is detected in patients with DR who were referred to eye clinics to assessed using random-effects hierarchical sROC meta-analysis models.
Abstract: Background
Diabetic macular oedema (DMO) is a thickening of the central retina, or the macula, and is associated with long-term visual loss in people with diabetic retinopathy (DR). Clinically significant macular oedema (CSMO) is the most severe form of DMO. Almost 30 years ago, the Early Treatment Diabetic Retinopathy Study (ETDRS) found that CSMO, diagnosed by means of stereoscopic fundus photography, leads to moderate visual loss in one of four people within three years. It also showed that grid or focal laser photocoagulation to the macula halves this risk. Recently, intravitreal injection of antiangiogenic drugs has also been used to try to improve vision in people with macular oedema due to DR.
Optical coherence tomography (OCT) is based on optical reflectivity and is able to image retinal thickness and structure producing cross-sectional and three-dimensional images of the central retina. It is widely used because it provides objective and quantitative assessment of macular oedema, unlike the subjectivity of fundus biomicroscopic assessment which is routinely used by ophthalmologists instead of photography. Optical coherence tomography is also used for quantitative follow-up of the effects of treatment of CSMO.
TL;DR: In this article, a synthetic aperture-based on-chip microscope was proposed to achieve a very large effective numerical aperture of 1.4 over a field-of-view (FOV) of >20 mm2.
Abstract: Wide field-of-view (FOV) and high-resolution imaging requires microscopy modalities to have large space-bandwidth products. Lensfree on-chip microscopy decouples resolution from FOV and can achieve a space-bandwidth product greater than one billion under unit magnification using state-of-the-art opto-electronic sensor chips and pixel super-resolution techniques. However, using vertical illumination, the effective numerical aperture (NA) that can be achieved with an on-chip microscope is limited by a poor signal-to-noise ratio (SNR) at high spatial frequencies and imaging artifacts that arise as a result of the relatively narrow acceptance angles of the sensor's pixels. Here, we report, for the first time, a synthetic aperture-based on-chip microscope in which the illumination angle is scanned across the surface of a dome to increase the effective NA of the reconstructed lensfree image to 1.4, achieving e.g., ∼250-nm resolution at 700-nm wavelength under unit magnification. This synthetic aperture approach not only represents the largest NA achieved to date using an on-chip microscope but also enables color imaging of connected tissue samples, such as pathology slides, by achieving robust phase recovery without the need for multi-height scanning or any prior information about the sample. To validate the effectiveness of this synthetic aperture-based, partially coherent, holographic on-chip microscope, we have successfully imaged color-stained cancer tissue slides as well as unstained Papanicolaou smears across a very large FOV of 20.5 mm2. This compact on-chip microscope based on a synthetic aperture approach could be useful for various applications in medicine, physical sciences and engineering that demand high-resolution wide-field imaging. An on-chip microscope that offers both a high-resolution and a wide field of view looks set to benefit the biological and physical sciences. The lensfree imaging device, developed by researchers at the University of California at Los Angeles, CA, USA, makes use a synthetic aperture approach to provide a very large effective numerical aperture of 1.4 over a field of view of >20 mm2; this is a much larger numerical aperture than previous lensfree approaches had realized (<0.9). Consequently, very high spatial resolution (for example, 250 nm at a wavelength of 700 nm) was achieved. By illuminating samples with light of three different wavelengths (470 nm, 532 nm and 632 nm), the researchers also obtained lens-free color images of samples such as breast cancer tissue.
TL;DR: The proposed method is shown effective to eliminate the projection artifacts in outer retinal space of OCT micro-angiography, resulting in better visualization of the pathological neovascularization when compared with the current common approaches.
Abstract: Current optical coherence tomography (OCT) based micro-angiography is prone to a projection (or tailing) effect due to the high scattering property of blood within overlying patent vessels, creating artifacts that interfere with the interpretation of retinal angiographic results. In this work, the projection effect in OCT micro-angiography is examined and its causality is explained by strong light scattering and photon propagation within blood. A simple practical approach is then introduced to minimize these artifacts presented in the outer retinal avascular space, especially useful for examining clinical cases with choroidal neovascularization (CNV). Demonstrated through in-vivo human posterior eye imaging of healthy and CNV subjects, the proposed method is shown effective to eliminate the projection artifacts in outer retinal space of OCT micro-angiography, resulting in better visualization of the pathological neovascularization when compared with the current common approaches. In addition, it is also shown that the proposed method is applicable to minimize the projection artifacts appearing in deep retinal layers.
TL;DR: An aggregate meta-analysis combining results from different studies that examined the RNFL thickness by means of OCT in AD and MCI patients compared with cognitively healthy controls supports the important role of OCT for RNFL analysis in monitoring the progression of AD and in assessing the effectiveness of purported AD treatments.
Abstract: Background
Alzheimer’s disease (AD) is a neurodegenerative disorder, which is likely to start as mild cognitive impairment (MCI) several years before the its full-blown clinical manifestation. Optical coherence tomography (OCT) has been used to detect a loss in peripapillary retina nerve fiber layer (RNFL) and a reduction in macular thickness and volume of people affected by MCI or AD. Here, we performed an aggregate meta-analysis combining results from different studies.
TL;DR: Retinal nerve fiber layer (RNFL) thinning, assessed by optical coherence tomography (OCT), has recently been reported in various dementias.
TL;DR: An overview of advanced image processing for three dimensional (3D) optical coherence tomographic (OCT) angiography of macular diseases, including age-related macular degeneration and diabetic retinopathy is provided.
Abstract: This article provides an overview of advanced image processing for three dimensional (3D) optical coherence tomographic (OCT) angiography of macular diseases, including age-related macular degeneration (AMD) and diabetic retinopathy (DR). A fast automated retinal layers segmentation algorithm using directional graph search was introduced to separates 3D flow data into different layers in the presence of pathologies. Intelligent manual correction methods are also systematically addressed which can be done rapidly on a single frame and then automatically propagated to full 3D volume with accuracy better than 1 pixel. Methods to visualize and analyze the abnormalities including retinal and choroidal neovascularization, retinal ischemia, and macular edema were presented to facilitate the clinical use of OCT angiography.
TL;DR: The use of OCT is described for detecting dental caries, tooth fractures, and interfacial gaps in intraoral restorations and can be a reliable and an accurate method and a safer alternative to X-ray radiography.
Abstract: Optical coherence tomography (OCT) is a noninvasive technique providing cross-sectional images of a tooth structure. This review describes the use of OCT for detecting dental caries, tooth fractures, and interfacial gaps in intraoral restorations. OCT can be a reliable and an accurate method and a safer alternative to X-ray radiography.
TL;DR: With optical coherence tomography angiography, it is possible to identify small intraretinal neov vascular complexes communicating with the deep retinal capillary plexus in eyes with Type 3 neovascularization secondary to age-related macular degeneration.
Abstract: Purpose:To characterize the vascular structure of Type 3 neovascularization secondary to age-related macular degeneration using optical coherence tomography angiography.Methods:Optical coherence tomography angiography cube scans (3 mm × 3 mm) were acquired in 29 eyes of 24 patients with Type 3 lesio
TL;DR: The results suggest that 100° FOV OCT is possible with current swept source OCT technology and investigate the origin of an angle dependent signal fall-off which is present in 85° and 100° single volume images, but not in the mosaic.
Abstract: We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85° FOV as well as with 100° and stitching of five 60° images to a 100° mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85° and 100° single volume images, but not in the mosaic. Our results suggest that 100° FOV OCT is possible with current swept source OCT technology.
TL;DR: Although clinical imaging and research microscopy are often isolated from one another, it is argued that their combination and integration is not only informative but also essential to discovering new biology and interpreting clinical datasets in which signals invariably originate from hundreds to thousands of cells per voxel.
Abstract: Imaging reveals complex structures and dynamic interactive processes, located deep inside the body, that are otherwise difficult to decipher. Numerous imaging modalities harness every last inch of the energy spectrum. Clinical modalities include magnetic resonance imaging (MRI), X-ray computed tomography (CT), ultrasound, and light-based methods [endoscopy and optical coherence tomography (OCT)]. Research modalities include various light microscopy techniques (confocal, multiphoton, total internal reflection, superresolution fluorescence microscopy), electron microscopy, mass spectrometry imaging, fluorescence tomography, bioluminescence, variations of OCT, and optoacoustic imaging, among a few others. Although clinical imaging and research microscopy are often isolated from one another, we argue that their combination and integration is not only informative but also essential to discovering new biology and interpreting clinical datasets in which signals invariably originate from hundreds to thousands of cells per voxel.
TL;DR: Improved differentiation of the ONL and HFL boundary is made possible by using directional OCT, a method that purposefully varies the pupil entrance position of the OCT beam to improve clinical trial endpoints and assessment of disease progression.
Abstract: Purpose:The outer nuclear layer (ONL) contains photoreceptor nuclei, and its thickness is an important biomarker for retinal degenerations. Accurate ONL thickness measurements are obscured in standard optical coherence tomography (OCT) images because of Henle fiber layer (HFL). Improved differentiat
TL;DR: This work combined photoacoustic ophthalmoscopy with spectral domain-optical coherence tomography with SD-OCT to tackle the challenge of quantifying retinal oxygen metabolic rate (rMRO2), and tested the integrated system on normal wild-type rats.
Abstract: Quantitatively determining physiological parameters at a microscopic level in the retina furthers the understanding of the molecular pathways of blinding diseases, such as diabetic retinopathy and glaucoma. An essential parameter, which has yet to be quantified noninvasively, is the retinal oxygen metabolic rate (rMRO2). Quantifying rMRO2 is challenging because two parameters, the blood flow rate and hemoglobin oxygen saturation (sO2), must be measured together. We combined photoacoustic ophthalmoscopy (PAOM) with spectral domain-optical coherence tomography (SD-OCT) to tackle this challenge, in which PAOM measured the sO2 and SD-OCT mapped the blood flow rate. We tested the integrated system on normal wild-type rats, in which the measured rMRO2 was 297.86 ± 70.23 nl/minute. This quantitative method may shed new light on both fundamental research and clinical care in ophthalmology in the future.
TL;DR: In some eyes with age-related macular degeneration, the earliest sign of Type 3 neovascularization is punctate hyperreflective foci above the external limiting membrane, and the mature Type 3 lesions and associated serous pigment epithelial detachments are highly responsive to anti-vascular endothelial growth factor therapy.
Abstract: Purpose:To demonstrate the evolution and treatment response of Type 3 neovascularization using spectral domain optical coherence tomography.Methods:We retrospectively analyzed 40 eyes treated with intravitreal anti-vascular endothelial growth factor therapy for Type 3 neovascularization over a varia
TL;DR: The split-spectrum amplitude-decorrelation angiography algorithm was optimized on a spectral optical coherence tomography system using a flow phantom to increase the detectable retinal microvascular flow and decrease the variability of the quantified vessel density in OCT retinal angiograms of healthy human subjects.
Abstract: The split-spectrum amplitude-decorrelation angiography algorithm was optimized on a spectral optical coherence tomography system using a flow phantom. The number of times the spectrum was split and the bandwidth of each split were adjusted to maximize the flow phantom decorrelation signal-to-noise ratio. The improvement in flow detection was then demonstrated with en face retinal angiograms. The optimized algorithm increased the detectable retinal microvascular flow and decreased the variability of the quantified vessel density in OCT retinal angiograms of healthy human subjects.
TL;DR: An automatic algorithm, OCTRIMA 3D (OCT Retinal IMage Analysis 3D), that could segment OCT volume data in the macular region fast and accurately is developed and is believed to be a leap forward towards achieving reliable, real-time analysis of 3D OCT retinal data.
Abstract: Optical coherence tomography (OCT) is a high speed, high resolution and non-invasive imaging modality that enables the capturing of the 3D structure of the retina. The fast and automatic analysis of 3D volume OCT data is crucial taking into account the increased amount of patient-specific 3D imaging data. In this work, we have developed an automatic algorithm, OCTRIMA 3D (OCT Retinal IMage Analysis 3D), that could segment OCT volume data in the macular region fast and accurately. The proposed method is implemented using the shortest-path based graph search, which detects the retinal boundaries by searching the shortest-path between two end nodes using Dijkstra’s algorithm. Additional techniques, such as inter-frame flattening, inter-frame search region refinement, masking and biasing were introduced to exploit the spatial dependency between adjacent frames for the reduction of the processing time. Our segmentation algorithm was evaluated by comparing with the manual labelings and three state of the art graph-based segmentation methods. The processing time for the whole OCT volume of 496×644×51 voxels (captured by Spectralis SD-OCT) was 26.15 seconds which is at least a 2-8-fold increase in speed compared to other, similar reference algorithms used in the comparisons. The average unsigned error was about 1 pixel (∼ 4 microns), which was also lower compared to the reference algorithms. We believe that OCTRIMA 3D is a leap forward towards achieving reliable, real-time analysis of 3D OCT retinal data.
TL;DR: An automated algorithm for CNV area detection relies on denoising and a saliency detection model to overcome issues such as projection artifacts and the heterogeneity of CNV.
Abstract: Optical coherence tomography angiography has recently been used to visualize choroidal neovascularization (CNV) in participants with age-related macular degeneration. Identification and quantification of CNV area is important clinically for disease assessment. An automated algorithm for CNV area detection is presented in this article. It relies on denoising and a saliency detection model to overcome issues such as projection artifacts and the heterogeneity of CNV. Qualitative and quantitative evaluations were performed on scans of 7 participants. Results from the algorithm agreed well with manual delineation of CNV area.
TL;DR: The defining OCT features of ORT are location in the outer nuclear layer, a hyperreflective band differentiating it from cysts, and retinal pigment epithelium that is either dysmorphic or absent.
Abstract: Purpose:To compare optical coherence tomography (OCT) and histology of outer retinal tubulation (ORT) secondary to advanced age-related macular degeneration in patients and in postmortem specimens, with particular attention to the basis of the hyperreflective border of ORT.Method:A private referral
TL;DR: The use of OCT angiography could greatly enrich the understanding of the ischemic processes affecting different layers of the retinal vasculature, such as cotton-wool spots to superficial plexus indices, paracentral acute middle maculopathy, and macular telangiectasia type 2.
Abstract: Fluorescein angiography has been the gold standard imaging modality for the retinal vasculature since its groundbreaking introduction in 1961 by Alvis and Novotny and has revolutionized our ability to diagnose diseases of the retinal vasculature and to identify retinal and choroidal neovascularization.1 Its greatest advantage may lie in its ability to detect dynamic patterns of dye transit and leakage. Various innovations have broadened the use of angiography, including the application of indocyanine green, wide-field image acquisition, confocal scanning laser ophthalmoscopy, and adaptive optics. However, a major limitation of traditional angiography resides in its inability to image the entire retinal capillary system or to directly visualize nascent vessels, leaving the practitioner to deduce the presence of neovascularization on the basis of other indicators such as fluid, leakage, or edema. Optical coherence tomography (OCT) angiography applies high-speed OCT scanning to detect blood flow by analyzing signal decorrelation between scans. Compared with stationary areas of the retina, the movement of erythrocytes within a vessel generates a decorrelated signal. The split-spectrum amplitude decorrelation angiography (SSADA) algorithm improves the signal to noise ratio by splitting the source spectrum into 4 parts and averaging the resultant 4 signals. High-density raster scanning of a 2-dimensional area of the retina generates a volumetric rendering of blood flow from the internal limiting membrane to the choroid and allows for direct visualization of normal and abnormal blood vessels. The currently available Optovue AngioVue System uses spectral-domain technology, an 840-nm laser, and the SSADA algorithm (Figure). The 70-kHz A-scan rate on this device allows a 3 × 3-mm OCT angiography volume to be acquired in 3 seconds. The lateral and axial resolutions are both 15 μm; the axial resolution is significantly less than that for structural OCT (5 μm) owing to signal averaging. Another device under development by Zeiss will feature a swept-source laser centered at 1040 nm with the potential for augmented signal penetration depth. Future devices may use other approaches for OCT angiography, such as phase contrast or intensity variance. Unlike traditional angiography, which uses a fluorescent dye and provides limited 3-dimensional information, OCT angiography requires no exogenous contrast and uses dense volumetric scanning to provide depth-resolved visualization of the retinal and choroidal vasculature. The retinal vasculature of the central macula is predominantly a 3-layered capillary bed. Even though one can identify the superficial retinal capillary plexus using fluorescein angiography, this angiographic technique poorly visualizes the intermediate and deep plexuses that are a critical focus of retinal vascular disease.1,2 Using the SSADA technique, Spaide et al1 were the first to demonstrate distinct superficial and deep capillary networks, the latter of which includes both the deep and intermediate plexuses. The use of OCT angiography could greatly enrich our understanding of the ischemic processes affecting different layers of the retinal vasculature, such as cotton-wool spots (superficial plexus ischemia), paracentral acute middle maculopathy (deep plexus ischemia),2 and macular telangiectasia type 2.3 Optical coherence tomography angiography may also have the potential to dissect the long-debated origin and microvascular anatomy of neovascularization in age-related macular degeneration, including type 1 (sub– retinal pigment epithelium), type 2 (subretinal), and type 3 (intraretinal; retinal angiomatous proliferation) neovascularization. In a seminal study, Jia et al4 generated 3-dimensional reconstructions of choroidal neovascularization and en face OCT renderings to highlight the precise vascular anatomy of choroidal neovascularization. It may be possible to identify distinct morphologies of choroidal neovascularization and then correlate these subtypes with disease course, prognosis, and response to treatment. In addition to providing enhanced anatomic detail, OCT angiography intrinsically generates data on vascular flow. This powerful feature has enormous implications for understanding tissue perfusion in the absence of obvious morphological changes. A flow index of the optic nerve head can be used to ascertain disc perfusion. For example, glaucomatous optic discs and discs damaged by optic neuritis have significantly diminished flow indices compared with normal discs.5,6 Remarkably, OCT angiographic measurements are sensitive
TL;DR: Applications of this novel platform include monitoring disease progression and pathophysiology in rodent models of Alzheimer's disease and subcortical dementias, including vascular dementia.
Abstract: A spectral/Fourier domain optical coherence tomography (OCT) intravital microscope using a supercontinuum light source at 1.7 μm was developed to study subcortical structures noninvasively in the living mouse brain. The benefits of 1.7 μm for deep tissue brain imaging are demonstrated by quantitatively comparing OCT signal attenuation characteristics of cortical tissue across visible and near-infrared wavelengths. Imaging of hippocampal tissue architecture and white matter microvasculature are demonstrated in vivo through thinned-skull, glass coverslip-reinforced cranial windows in mice. Applications of this novel platform include monitoring disease progression and pathophysiology in rodent models of Alzheimer’s disease and subcortical dementias, including vascular dementia.