Comparison of amplitude-decorrelation, speckle-variance and phase-variance OCT angiography methods for imaging the human retina and choroid.
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ABSTRACT:
SUBMITTER: Gorczynska I
PROVIDER: S-EPMC4866465 | biostudies-other | 2016 Mar
REPOSITORIES: biostudies-other
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Project description:Speckle, amplitude fluctuations in optical coherence tomography (OCT) images, contains information on sub-resolution structural properties of the imaged sample. Speckle statistics could therefore be utilized in the characterization of biological tissues. However, a rigorous theoretical framework relating OCT speckle statistics to structural tissue properties has yet to be developed. As a first step, we present a theoretical description of OCT speckle, relating the OCT amplitude variance to size and organization for samples of discrete random media (DRM). Starting the calculations from the size and organization of the scattering particles, we analytically find expressions for the OCT amplitude mean, amplitude variance, the backscattering coefficient and the scattering coefficient. We assume fully developed speckle and verify the validity of this assumption by experiments on controlled samples of silica microspheres suspended in water. We show that the OCT amplitude variance is sensitive to sub-resolution changes in size and organization of the scattering particles. Experimentally determined and theoretically calculated optical properties are compared and in good agreement.
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Project description:PurposeTo compare the quality of four OCT-angiography(OCT-A) modules.MethodThe retina of nineteen healthy volunteers were scanned with four OCT-devices (Topcon DRI-OCT Triton Swept-source OCT, Optovue RTVue-XR, a prototype Spectralis OCT2, Heidelberg-Engineering and Zeiss Cirrus 5000-HD-OCT). The device-software generated en-face OCT-A images of the superficial (SCP) and deep capillary plexuses (DCP) were evaluated and scored by 3 independent retinal imaging experts. The SCP vessel density was assessed using Angiotool-software. After the inter-grader reliability assessment, a consensus grading was performed and the modules were ranked based on their scoring.ResultsThere was no significant difference in the vessel density among the modules (Zeiss 48.7±4%, Optovue 47.9±3%, Topcon 48.3±2%, Heidelberg 46.5±4%, p = 0.2). The numbers of discernible vessel-bifurcations differed significantly on each module (Zeiss 2±0.9 bifurcations, Optovue 2.5±1.2, Topcon 1.3±0.7 and Heidelberg 0.5±0.6, p≤0.001). The ranking of each module differed depending on the evaluated parameter. In the overall ranking, the Zeiss module was superior and in 90% better than the median (Bonferroni corrected p-value = 0.04). Optovue was better than the median in 60%, Topcon in 40% and Heidelberg module in 10%, however these differences were not statistically significant.ConclusionEach of the four evaluated OCT-A modules had particular strengths, which differentiated it from their competitors.
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Project description:PurposeWe measured reproducibility of speckle-noise freed fluid and tissue compartmentalization of the choroid (choroidal angiography and tissue characterization).MethodsThis study included 26 eyes of 13 healthy females: 13 were used for repeated measurements and 13 were used for side comparison. A semiautomated algorithm removed speckle-noise with structure preservation.ResultsIntraclass correlation (ICC), with respect to reproducibility of the method, showed an ICC for choroidal fluid inner space analysis (FISA) of 95.15% (90.01-98.24). The ICC of tissue inner space analysis (TISA) was 99.75% (99.47-99.91). The total choroid ratio (TCR), calculated from volumes of tissue to vessels, showed an ICC of 88.84% (78.28-95.82). Comparison of eyes (left to right) showed a difference for FISA of 0.033 (95% confidence interval [CI] -0.0018-0.0680, P = 0.063), TISA -0.118 (CI -0.2373-0.0023, P = 0.055), and TCR -0.590 (CI -0.9047 to -0.2754, P = 0.004). The ICC for FISA and TISA showed a trend in the difference comparing left and right eyes; however, TCR showed a significant difference between the eyes in the measured area (P < 0.001). Mean overall FISA was 0.58 mm3 (range, 0.25-0.98 mm3, SD = 0.14). Mean TISA was 3.45 mm3 (range, 2.38-5.0 mm3, SD 0.072). Mean TCR was 6.13 (overall range, 3.93-10.2, SD = 1.34).ConclusionsDifferences in choroidal layers between subjects were found mainly due to alterations in choroidal tissue. Reproducibility of speckle-noise freed choroidal angiography appeared excellent.Translational relevanceSpeckle noise is a granular "noise" that appears in a wide range of medical imaging methods as ultrasonography, magnetic resonance, computer tomography, or optical coherence tomography (OCT). Findings from basic science about speckle noise were translated into a novel, medical image postprocessing application that can separate signal from speckle noise with structure preservation with high reproducibility and enhance medical imaging.
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Project description:Phase amplitude coupling (PAC) is thought to play a fundamental role in the dynamic coordination of brain circuits and systems. There are however growing concerns that existing methods for PAC analysis are prone to error and misinterpretation. Improper frequency band selection can render true PAC undetectable, while non-linearities or abrupt changes in the signal can produce spurious PAC. Current methods require large amounts of data and lack formal statistical inference tools. We describe here a novel approach for PAC analysis that substantially addresses these problems. We use a state space model to estimate the component oscillations, avoiding problems with frequency band selection, nonlinearities, and sharp signal transitions. We represent cross-frequency coupling in parametric and time-varying forms to further improve statistical efficiency and estimate the posterior distribution of the coupling parameters to derive their credible intervals. We demonstrate the method using simulated data, rat local field potentials (LFP) data, and human EEG data.
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Project description:In recent years, advances in optical coherence tomography (OCT) techniques have increased our understanding of diabetic retinopathy, an important microvascular complication of diabetes. OCT angiography is a non-invasive method that visualizes the retinal vasculature by detecting motion contrast from flowing blood. Visible-light OCT shows promise as a novel technique for quantifying retinal hypoxia by measuring the retinal oxygen delivery and metabolic rates. In this article, we discuss recent insights provided by these techniques into the vascular pathophysiology of diabetic retinopathy. The next milestones for these modalities are large multicenter studies to establish consensus on the most reliable and consistent outcome parameters to study diabetic retinopathy.
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Project description:Purpose:To compare review strategies for optical coherence tomography angiography (OCT-A) for multiple disease features found in common diseases of the choroid and retina. Design:Prospective, observational study. Participants:Patients with macular disease undergoing routine spectral-domain optical coherence tomography (SDOCT). Methods:Eyes were imaged with the Avanti RTVue XR HD (Optovue, Fremont, CA), and the split-spectrum amplitude decorrelation angiography (SSADA) algorithm software was utilized for OCT-A performance. Scans were reviewed by 2 masked expert reviewers. A third masked reviewer was utilized in cases of reviewer disagreement. A single report using automated segmentation within the Avanti software to represent the superficial retina capillary plexus, deep retina capillary plexus, outer retina, and choroid capillary layer was generated. A continuous slab descent video export was also reviewed for each OCT-A scan. This video consisted of a continuous (e.g., line-by-line) review of the en face OCT- data. Each dataset was reviewed for the presence of three pathologic features: choroidal neovascularization, microaneurysms, and macular ischemia. Main Outcome Measures:Comparison of identification rates of retinal and choroidal microvascular abnormalities using different review strategies. Results:Four hundred twenty-one eyes were included in the study. Of those, 350 eyes had reports that were deemed sufficient quality for interpretation and analysis by both reviewers. Identification rates of choroidal neovascularization, microaneurysms, and macular ischemia on the report were 90.5%, 84.5%, and 95.4% respectively compared to the overall presence. Likewise, rates of identification in the continuous slab descent review video were 88.1%, 96.4%, and 95.4% for choroidal neovascularization, microaneurysms, and macular ischemia respectively compared to the overall presence. Cohen's kappa values ranged from 0.80 to 0.96, corresponding to very good agreement between the report and continuous slab descent review for each variable. Conclusions:Defining an optimal reporting strategy for OCT-A is important for diagnostic accuracy and optimizing workflow in retina clinics. In this study, OCT-A report using automated segmentation was comparable to continuous slab descent review for identifying microvascular abnormalities of the retina and choroid.
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Project description:PurposeTo determine peripapillary vessel density in eyes with perimetric glaucoma (PG) or preperimetric glaucoma (PPG) compared to normal controls using optical coherence tomography-angiography (OCT-A).MethodsWe recruited 13 patients with unilateral perimetric normal-tension glaucoma (NTG) and fellow preperimetric NTG showing only inferotemporal retinal nerve fiber layer (RNFL) defect in red-free RNFL photography in both eyes. We also enrolled 9 healthy controls. Using OCT-A, radial peripapillary capillary densities at inferotemporal and superotemporal regions were evaluated. Paired comparison of peripapillary vessel density was performed for PG eye, PPG eye, and normal eye.ResultsA total of 26 eyes of the 13 patients with unilateral PG and fellow PPG eyes and 18 eyes of 9 normal controls were analyzed. Vessel densities at the whole peripapillary region and inferotemporal region in PG eyes were significantly lower than those in PPG eyes (P = 0.001, P<0.001, respectively). Comparison between PPG and normal eyes showed no significant difference in the whole peripapillary region or the inferotemporal region (P = 0.654, P = 0.174, respectively). There was no significant (P = 0.288) difference in vessel density at superotemporal region among the three types of eyes (PG eye, PPG eye, and normal eye).ConclusionPPG eyes and normal eyes were found to have the similar densities of peripapillary microvasculature at the area with nerve fiber layer defect, whereas in PG eye, there was a significant decrease in vessel density at the area of RNFL thinning. This provides evidence that microvascular compromise in the retina might be a secondary change to nerve fiber layer degeneration in the pathogenesis of NTG.
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