To describe image artifacts of optical coherence tomography (OCT) angiography and their underlying causative mechanisms. To establish a common vocabulary for the artifacts observed.
The methods by ...which OCT angiography images are acquired, generated, and displayed are reviewed as are the mechanisms by which each or all of these methods can produce extraneous image information. A common set of terminology is proposed and used.
Optical coherence tomography angiography uses motion contrast to image blood flow and thereby images the vasculature without the need for a contrast agent. Artifacts are very common and can arise from the OCT image acquisition, intrinsic characteristics of the eye, eye motion, image processing, and display strategies. Optical coherence tomography image acquisition for angiography takes more time than simple structural scans and necessitates trade-offs in flow resolution, scan quality, and speed. An important set of artifacts are projection artifacts in which images of blood vessels seem at erroneous locations. Image processing used for OCT angiography can alter vascular appearance through segmentation defects, and because of image display strategies can give false impressions of the density and location of vessels. Eye motion leads to discontinuities in displayed data. Optical coherence tomography angiography artifacts can be detected by interactive evaluation of the images.
Image artifacts are common and can lead to incorrect interpretations of OCT angiography images. 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.
Optical coherence tomography angiography Spaide, Richard F.; Fujimoto, James G.; Waheed, Nadia K. ...
Progress in retinal and eye research,
05/2018, Volume:
64
Journal Article
Peer reviewed
Open access
Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina ...and choroid with levels of detail far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
To describe the characteristics as well as the sensitivity and specificity of detection of choroidal neovascularization (CNV) on optical coherence tomography angiography (OCTA) using spectral-domain ...optical coherence tomography.
Observational, retrospective study.
Seventy-two eyes of 61 subjects (48 eyes of 43 subjects with CNV, 24 eyes of 18 subjects without CNV).
Patients imaged using the prototype AngioVue OCTA system (Optovue, Inc, Fremont, CA) between August 2014 and October 2014 at New England Eye Center were assessed. Patients in whom CNV was identified on OCTA were evaluated to define characteristics of CNV on OCTA: size using greatest linear dimension (small, <1 mm; medium, 1-2 mm; large, >2 mm), appearance (well-circumscribed, poorly circumscribed), and presence of subretinal and intraretinal fluid. Concurrently, an overlapping second cohort of patients who underwent same-day OCTA and fluorescein angiography (FA) for suspected CNV was evaluated to estimate sensitivity and specificity of OCTA in detecting CNV using FA as ground truth.
Choroidal neovascularization appearance, CNV size, and presence of subretinal and intraretinal fluid.
In 48 eyes, CNV was visualized on OCTA. Thirty-one eyes had CNV associated with neovascular age-related macular degeneration. Size of CNV was small in 23% (7/31), medium in 42% (13/31), and large in 35% (11/31). Poorly circumscribed vessels, subretinal fluid, and intraretinal fluid each were seen in 71% (22/31). Seven eyes had CNV associated with central serous chorioretinopathy. Size of CNV was small in 71% (5/7) and large in 29% (2/7). Seventy-one percent (5/7) had well-circumscribed vessels, 86% (6/7) had subretinal fluid, and 14% (1/7) had intraretinal fluid. Thirty eyes with OCTA and same-day FA were evaluated to determine sensitivity and specificity of CNV detection on OCTA. Sensitivity was 50% (4/8) and specificity was 91% (20/22).
Using OCTA allows the clinician to visualize CNV noninvasively and may provide a method for identifying and guiding treatment of CNV. The specificity of CNV detection on OCTA compared with FA seems to be high. Future studies with larger sample sizes are needed to elaborate better on the sensitivity and specificity of CNV detection and to illustrate clinical usefulness.
The body of knowledge of in vivo investigation of the choroid has been markedly enhanced by recent technological advances in optical coherence tomography (OCT). New insights elucidating the ...morphological features of the choriocapillaris and choroidal vasculature, in both physiological and pathological conditions, indicate that the choroid plays a pivotal role in many posterior segment diseases. In this article, a review of the histological characteristics of the choroid, which must be considered for the proper interpretation of in vivo imaging, is followed by a comprehensive discussion of fundamental principles of the current state-of-the-art in OCT, including cross-sectional OCT, en face OCT, and OCT angiography using both spectral domain OCT and swept source OCT technologies. A detailed review of the tomographic features of the choroid in the normal eye is followed by relevant findings in prevalent chorioretinal diseases, focusing on major causes of vision loss such as typical early and advanced age-related macular degeneration, polypoidal choroidal vasculopathy, central serous chorioretinopathy, pachychoroid spectrum disorders, diabetic choroidopathy, and myopia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
IMPORTANCE Diabetic retinopathy (DR) is characterized by microaneurysms, capillary nonperfusion, and ischemia within the retina, ultimately leading to neovascularization and/or macular edema. ...Evidence suggests that choroidal angiopathy may coexist with retinal vascular damage. Recent advances in spectral-domain optical coherence tomography (SD-OCT) permit an efficient visualization of the choroid. OBJECTIVE To analyze the morphological features and vascular layers of the choroid in patients with DR using SD-OCT. DESIGN A cross-sectional retrospective review identified patients with DR and healthy (control) subjects who underwent 1-line raster scanning from February 1, 2010, through June 30, 2012. Patients were classified into the following 3 groups: nonproliferative DR without macular edema (9 eyes), proliferative DR without macular edema (PDR) (10 eyes), and diabetic macular edema (DME) (14 eyes). Two independent raters experienced in analyzing OCT images evaluated the morphological features and vasculature of the choroid. SETTING New England Eye Center. PARTICIPANTS Thirty-three eyes of 33 patients with DR and 24 eyes of 24 controls. EXPOSURE Diabetic retinopathy. MAIN OUTCOME AND MEASURE Choroidal morphological features and vasculature analysis. RESULTS The choroidoscleral interface had an irregular contour in 8 of 9 eyes with nonproliferative DR (89%), 9 of 10 eyes with PDR (90%), and 13 of 14 eyes with DME (93%) compared with 0 of 24 controls. The thickest point of the choroid was displaced from under the fovea, and focal choroidal thinning was observed in eyes with DR. Mean subfoveal choroidal thickness and mean subfoveal medium choroidal vessel layer and choriocapillaris layer thickness were significantly reduced in eyes with PDR (P < .05) and DME (P < .05) compared with controls. CONCLUSIONS AND RELEVANCE Choroidal morphological features are altered in patients with moderate to severe DR. The subfoveal choroidal thickness and the subfoveal medium choroidal vessel layer and choriocapillaris layer thicknesses are significantly reduced in patients with PDR and DME. To our knowledge, this is the first study to analyze the morphological features and vasculature of the choroid in DR using SD-OCT. These findings may be clinically useful in predicting the progression of DR.
Optical coherence tomography angiography (OCTA) is a new, non-invasive imaging technique that generates volumetric angiography images in a matter of seconds. This is a nascent technology with a ...potential wide applicability for retinal vascular disease. At present, level 1 evidence of the technology's clinical applications doesn't exist. In this paper, we introduce the technology, review the available English language publications regarding OCTA, and compare it with the current angiographic gold standards, fluorescein angiography (FA) and indocyanine green angiography (ICGA). Finally we summarize its potential application to retinal vascular diseases. OCTA is quick and non-invasive, and provides volumetric data with the clinical capability of specifically localizing and delineating pathology along with the ability to show both structural and blood flow information in tandem. Its current limitations include a relatively small field of view, inability to show leakage, and proclivity for image artifact due to patient movement/blinking. Published studies hint at OCTA's potential efficacy in the evaluation of common ophthalmologic diseases such age related macular degeneration (AMD), diabetic retinopathy, artery and vein occlusions, and glaucoma. OCTA can detect changes in choroidal blood vessel flow and can elucidate the presence of choroidal neovascularization (CNV) in a variety of conditions but especially in AMD. It provides a highly detailed view of the retinal vasculature, which allows for accurate delineation of the foveal avascular zone (FAZ) in diabetic eyes and detection of subtle microvascular abnormalities in diabetic and vascular occlusive eyes. Optic disc perfusion in glaucomatous eyes is notable as well on OCTA. Further studies are needed to more definitively determine OCTA's utility in the clinical setting and to establish if this technology may offer a non-invasive option of visualizing the retinal vasculature in detail.
Binarization is a critical technique in optical coherence tomography angiography (OCTA) image analysis, but there is no consistency in the method used in published OCTA studies. This study assessed ...whether differences in OCTA binarization and brightness and contrast adjustments affect quantification measurements.
Prospective cross-sectional validity study.
This was a single-center study examining 21 eyes of 11 healthy individuals. All eyes were imaged using a swept-source OCTA (Zeiss), and quantitative measurements resulting from five binarization thresholding and five brightness/contrast adjustment methods were compared. All measurements were calculated for the superficial plexus and choriocapillaris (CC), as well as unaveraged and averaged en face OCTA images.
There were statistically significant differences between measurements from different binarization thresholding methods (P < 0.0001), as well as measurements from different histogram adjustments (P < 0.0001). The binarization thresholds yielded different measurements when combined with variable brightness/contrast adjustments. The method of analysis also affected the directionality of trends in imaging measurements between unaveraged and averaged CC images.
The method of OCTA image binarization thresholding and histogram adjustment significantly alters quantitative measurements and the directionality of trends. Results obtained from different OCTA binarization methods should be seen as valid only for that given method. This has significant consequences for clinical trials using OCTA measurements as outcome measurements. A consensus is needed across the research community for a consistent method for OCTA image quantification and greater attention paid to fully describing methods in published studies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Purpose To analyze type 1 neovascular membranes in age-related macular degeneration (AMD) using optical coherence tomography (OCT) angiography, to correlate morphologic characteristics with imaging ...and clinical criteria, and to analyze structural features of type 1 neovascularization sequentially after anti–vascular endothelial growth factor (VEGF) therapy. Design Prospective interventional case series. Methods Macular OCT angiography images were acquired using the RTVue XR Avanti with AngioVue. Distinct morphologic patterns and quantifiable features of the neovascular membranes were studied on en face projection images at baseline and follow-up. Results Thirty-three eyes of 25 patients were included. In 75% of the eyes, a highly organized vascular complex could be identified. A large main central vessel trunk/feeder vessel could be seen in 72% of these eyes, with vessels radiating in a branching pattern either in all directions from the center of the lesion (“medusa” pattern), or from one side of the lesion (“seafan” pattern). Of the 18 eyes with follow-up OCT angiography, the lesion area and vessel density remained unchanged, even after anti–vascular endothelial growth factor (VEGF) therapy, indicating a more mature longstanding neovascular complex resistant to anti-VEGF therapy. Conclusions OCT angiography provides a unique opportunity to study the morphology of occult type 1 neovascular membranes in AMD and allows precise structural and vascular assessment noninvasively. We identified a large mature neovascular complex in approximately 75% of eyes, typically consisting of a feeder vessel and large branching vessels resistant to anti-VEGF therapy. OCT angiography may better guide evaluation and treatment of neovascular AMD, and may contribute to the development of improved therapies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
To investigate ultrahigh-speed, swept-source optical coherence tomography (SSOCT) angiography for visualizing vascular changes in eyes with nonexudative age-related macular degeneration (AMD) with ...geographic atrophy (GA).
Observational, prospective, cross-sectional study.
A total of 63 eyes from 32 normal subjects and 12 eyes from 7 patients with nonexudative AMD with GA.
A 1050-nm, 400-kHz A-scan rate SSOCT system was used to perform volumetric optical coherence tomography angiography (OCTA) of the retinal and choriocapillaris (CC) vasculatures in normal subjects and patients with nonexudative AMD with GA. Optical coherence tomography angiography using variable interscan time analysis (VISTA) was performed to assess CC alteration and differentiate varying degrees of CC flow impairment.
Qualitative comparison of retinal and CC vasculatures in normal subjects versus those in patients with a clinical diagnosis of nonexudative AMD with GA.
In all 12 eyes with GA, OCTA showed pronounced CC flow impairment within the region of GA. In 10 of the 12 eyes with GA, OCTA with VISTA showed milder CC flow impairment extending beyond the margin of GA. Of the 5 eyes exhibiting foveal-sparing GA, OCTA showed CC flow within the region of foveal sparing in 4 of the eyes.
The ability of ultrahigh-speed, swept-source OCTA to noninvasively visualize alterations in the retinal and CC vasculatures makes it a promising tool for assessing nonexudative AMD with GA. Optical coherence tomography angiography using VISTA can distinguish varying degrees of CC alteration and flow impairment and may be useful for elucidating disease pathogenesis, progression, and response to therapy.
To analyze the long-term growth patterns of type 1 neovascularization (NV) in eyes with age-related macular degeneration (AMD) receiving anti–vascular endothelial growth factor (VEGF) therapy.
...Retrospective cohort study.
Patients were enrolled from 2 eye centers and underwent optical coherence tomography angiography (OCTA) imaging with follow-up greater than 1 year. Choroidal neovascularization (CNV) was manually segmented on OCTA images and compared between time points. CNV growth was subdivided into 3 categories based on OCTA area measurement: CNV doubling, modest growth of less than 50%, and shrinkage. These growth rates were correlated with OCTA morphologic features.
Forty-one eyes were analyzed. Mean CNV area was 1.60 ± 1.84 mm2 at baseline and 1.80 ± 1.84 mm2 at 1 year. Thirty-three eyes (80%) displayed an increase in CNV area at 1 year with a mean increase of 0.20 ± 0.38 mm2 (P = .001). Eleven eyes (27%) underwent CNV doubling, 19 eyes (46%) illustrated modest growth, and 6 (15%) showed shrinkage. Anatomic features including a capillary fringe (odds ratio OR = 5.3, P = .036) and immature lesion morphology (OR = 4.2, P = .015) were significantly associated with CNV doubling. CNV growth occurred in 3 predominant patterns: “symmetric” growth, “asymmetric” growth, and “finger-like projections,” which reflected the orientation of expansion of CNV. “Symmetric” and “asymmetric” growth together correlated with greater frequency of CNV doubling (OR = 15, P = .0048).
OCTA provides noninvasive measurement of the area of neovascular lesions in AMD. Sustained growth of type 1 NV can be identified in the majority of lesions (80%) that display characteristic patterns of progression despite ongoing anti-VEGF therapy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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