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Phase stable swept-source optical coherence tomography with active mode-locking laser for contrast enhancements of retinal angiography.

ABSTRACT: Swept-source optical coherence tomography (SS-OCT) is an attractive high-speed imaging technique for retinal angiography. However, conventional swept lasers vary the cavity length of the laser mechanically to tune the output wavelength. This causes sweep-timing jitter and hence low phase stability in OCT angiography. Here, we improve an earlier phase-stabilized, akinetic, SS-OCT angiography (OCTA) method by introducing coherent averaging. We develop an active mode-locking (AML) laser as a high phase-stable akinetic swept source for the OCTA system. The phase stability of the improved system was analyzed, and the effects of coherent averaging were validated using a retina phantom. The effectiveness of the coherent averaging method was further confirmed by comparing coherently and conventionally averaged en face images of human retinal vasculature for their contrast-to-noise ratio, signal-to-noise ratio, and vasculature connectivity. The contrast-to-noise ratio was approximately 1.3 times larger when applying the coherent averaging method in the human retinal experiment. Our coherent averaging method with the high phase-stability AML laser source for OCTA provides a valuable tool for studying healthy and diseased retinas.

SUBMITTER: Park KS

PROVIDER: S-EPMC8371173 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging.

Project description:Optical coherence tomography (OCT) is a noninvasive imaging modality that can provide high-resolution, cross-sectional images of tissues. Especially in retinal imaging, OCT has become one of the most valuable imaging tools for diagnosing eye diseases. Considering the scattering and absorption properties of the eye, the 1000-nm OCT system is preferred for retinal imaging. In this study, we describe the use of an akinetic swept-source OCT system based on a pulse-modulated active mode locking (AML) fiber laser at a 1080-nm wavelength for in-vivo human retinal imaging. The akinetic AML wavelength-swept fiber laser was constructed with polarization-maintaining fiber that has an average linewidth of 0.625?nm, a spectral bandwidth of 81.15?nm, and duty ratio of 90% without the buffering method. We successfully obtained in-vivo human retinal images using the proposed OCT system without the additional k-clock and the frequency shifter that provides a wide field of view of 43.1°. The main retina layers, such as the retinal pigment epithelium, can be distinguished from the OCT image with an axial resolution of 6.3 ?m with this OCT system.

| S-EPMC6281618 | biostudies-literature

Choroidal Neovascularization Analyzed on Ultrahigh-Speed Swept-Source Optical Coherence Tomography Angiography Compared to Spectral-Domain Optical Coherence Tomography Angiography.

Project description:PurposeTo compare visualization of choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD) using an ultrahigh-speed swept-source (SS) optical coherence tomography angiography (OCTA) prototype vs a spectral-domain (SD) OCTA device.DesignComparative analysis of diagnostic instruments.MethodsPatients were prospectively recruited to be imaged on SD OCT and SS OCT devices on the same day. The SD OCT device employed is the RTVue Avanti (Optovue, Inc, Fremont, California, USA), which operates at ∼840 nm wavelength and 70 000 A-scans/second. The SS OCT device used is an ultrahigh-speed long-wavelength prototype that operates at ∼1050 nm wavelength and 400 000 A-scans/second. Two observers independently measured the CNV area on OCTA en face images from the 2 devices. The nonparametric Wilcoxon signed rank test was used to compare area measurements and P values of <.05 were considered statistically significant.ResultsFourteen eyes from 13 patients were enrolled. The CNV in 11 eyes (78.6%) were classified as type 1, 2 eyes (14.3%) as type 2, and 1 eye (7.1%) as mixed type. Total CNV area measured using SS OCT and SD OCT 3 mm × 3 mm OCTA were 0.949 ± 1.168 mm(2) and 0.340 ± 0.301 mm(2), respectively (P = .001). For the 6 mm × 6 mm OCTA the total CNV area using SS OCT and SD OCT were 1.218 ± 1.284 mm(2) and 0.604 ± 0.597 mm(2), respectively (P = .0019). The field of view did not significantly affect the measured CNV area (P = .19 and P = .18 for SS OCT and SD OCT, respectively).ConclusionSS OCTA yielded significantly larger CNV areas than SD OCTA. It is possible that SS OCTA is better able to demarcate the full extent of CNV vasculature.

| S-EPMC4811690 | biostudies-literature

Swept-source optical coherence tomography angiography findings in choroidal and retinal tumors.

Project description:ObjectivesTo report the swept-source optical coherence tomography angiography (SS-OCTA) findings in choroidal and retinal tumors.MethodsA retrospective noncomparative interventional case series of 60 eyes having various choroidal and retinal tumors imaged with SS-OCTA (Topcon DR1 Triton Plus, Tokyo, Japan) between September 2018 and February 2020 was conducted. Inclusion criteria were tumor thickness <4 mm, tumor base diameter <10 mm, and tumor location at the posterior pole.ResultsChoroidal nevi usually demonstrated well-defined borders, hyperreflective internal structure, and no outer retinal involvement on SS-OCTA. Choroidal melanoma, in contrast to nevi, usually had ill-defined borders (p = 0.018), mixed hyperreflective-hyporeflective or hyperreflective internal structure (p = 0.014), and demonstrated outer retinal involvement (p < 0.001). Circumscribed choroidal hemangioma usually presented with well-defined borders, a hyperreflective internal tumor structure with multiple dilated interconnected tumor vessels intermixed with signal void areas representing connective tissue. Optic disc melanocytomas showed a hyporeflective plexus related to blocking of signal by the pigment and an intact radial peripapillary capillary network. There was flow on the surface and slightly deeper within the lesion on B-scan angiography overlay. Retinal astrocytic hamartomas had well-defined borders and a hyperreflective vascular plexus in the superficial and deep retina. Outer retina and choriocapillaris showed hyporeflective change due to shadowing/masking from calcium or high blood flow in the lesion.ConclusionsEach of the different retinal and choroidal tumors studied in this series presented with different SS-OCTA features to aid in the differential diagnosis of these conditions. Good quality images are obtained in patients with good fixation and tumors <3 mm in thickness located at the posterior pole.

| S-EPMC7853135 | biostudies-literature

Vascular Patterns in Retinitis Pigmentosa on Swept-Source Optical Coherence Tomography Angiography.

Project description:Retinitis Pigmentosa (RP) represents a retinal dystrophy with an extremely complex pathogenesis further worsened by the impairment of the retinal vascular supply. The main goal of this study was to identify different vascular patterns in RP, by means of optical coherence tomography angiography (OCTA). A total of 32 RP patients (16 males, 50%; mean age 45.93 ± 11.4) and 32 healthy age-matched controls (16 males, 50%; age 42.8 ± 11.2). High resolution OCT and OCTA images were obtained from all participants. Several quantitative parameters were extracted both from structural OCT and OCTA images. A post-hoc analysis assessed the relationship between the quantitative OCTA parameters adopted and the following measures: best corrected visual acuity (BCVA), central macular thickness (CMT) and retinal nerve fiber layer (RNFL). Mean LogMAR BCVA was 0.24 ± 0.32 for RP patients and 0.0 ± 0.0 for controls (p < 0.01). CMT, choroidal thickness and RNFL were statistically different between RP and controls (p < 0.01). OCTA parameters showed strong alterations of the retinal vascular network in RP (all p < 0.01). Several statistically significant correlations were also found. Furthermore, a vessel tortuosity cut-off of 4.80 and a vessel rarefaction cut-off of 0.62 enabled the RP cohort to be divided into two significantly different sub-groups in terms of BCVA, RNFL and CMT. Quantitative OCTA parameters help identify vascular abnormalities in RP, separating two different vascular patterns.

| S-EPMC6780333 | biostudies-literature

Swept-source optical coherence tomography angiography findings of diabetic papillopathy after intravitreal bevacizumab.

Project description:Purpose:We report a case of diabetic papillopathy (DP) treated with intravitreal bevacizumab injections and evaluated for disc vessel changes using swept-source optical coherence tomography angiography (SS-OCTA). Observations:A 52-year-old man was referred with a 1-week history of acute painless decreased vision in both eyes (OU). His best-corrected visual acuity (BCVA) was 20/40 in the right eye (OD) and 20/100 in the left eye (OS). Fundus examination showed swollen optic discs with superficial radially oriented telangiectatic vessels, peripapillary splinter hemorrhages, and hard exudates OU. On SS-OCTA, B-scan images displayed blood flow signals in the thickened retinal nerve fiber layer (RNFL) of the optic disc and superficial RNFL slab images displayed radially oriented telangiectatic vessels OU. Laboratory tests revealed previously unknown diabetes, and we diagnosed the patient with DP OU. Two weeks after an intravitreal injection of bevacizumab OS, the disc swelling, radially oriented telangiectatic vessels, and peripapillary splinter hemorrhages had decreased OS. The superficial RNFL slab OS also depicted decreased radially oriented telangiectatic vessels. However, OD showed no interval changes. Two weeks after an intravitreal bevacizumab injection OD, improved BCVA, decreased disc swelling, radially oriented telangiectatic vessels, and peripapillary splinter hemorrhages were observed OU. The superficial RNFL slab also showed decreased radially oriented telangiectatic vessels OU. Conclusions and importance:This case showed that bevacizumab is a useful treatment option for DP as they resolve underlying optic nerve capillary vasculopathy. SS-OCTA demonstrated resolved superficial telangiectatic vessels of the optic disc which has not been previously described.

| S-EPMC7256312 | biostudies-literature

4D optical coherence tomography-based micro-angiography achieved by 1.6-MHz FDML swept source.

Project description:We demonstrate the use of an ultra-high-speed swept-source optical coherence tomography (OCT) to achieve optical micro-angiography (OMAG) of microcirculatory tissue beds in vivo. The system is based on a 1310-nm Fourier domain mode-locking (FDML) laser with 1.6-MHz A-line rate, providing a frame rate of 3.415 KHz, an axial resolution of ?10???m and signal to noise ratio of 102 dB. Motion from blood flow causes change in OCT signals between consecutive B-frames acquired at the same location. Intensity-based inter-frame subtraction algorithm is applied to extract blood flow from tissue background without any motion correction. We demonstrate the capability of this 1.6-MHz OCT system for 4D OMAG of in vivo tissue at a volume rate of 4.7 volumes/s (volume size: 512×200×720 voxels).

| S-EPMC4612623 | biostudies-literature

9.4 MHz A-line rate optical coherence tomography at 1300 nm using a wavelength-swept laser based on stretched-pulse active mode-locking.

Project description:In optical coherence tomography (OCT), high-speed systems based at 1300 nm are among the most broadly used. Here, we present 9.4 MHz A-line rate OCT system at 1300 nm. A wavelength-swept laser based on stretched-pulse active mode locking (SPML) provides a continuous and linear-in-wavenumber sweep from 1240 nm to 1340 nm, and the OCT system using this light source provides a sensitivity of 98 dB and a single-sided 6-dB roll-off depth of 2.5 mm. We present new capabilities of the 9.4 MHz SPML-OCT system in three microscopy applications. First, we demonstrate high quality OCTA imaging at a rate of 1.3 volumes/s. Second, by utilizing its inherent phase stable characteristics, we present wide dynamic range en face Doppler OCT imaging with multiple time intervals ranging from 0.25 ms to 2.0 ms at a rate of 0.53 volumes/s. Third, we demonstrate video-rate 4D microscopic imaging of a beating Xenopus embryo heart at a rate of 30 volumes/s. This high-speed and high-performance OCT system centered at 1300 nm suggests that it can be one of the most promising high-speed OCT platforms enabling a wide range of new scientific research, industrial, and clinical applications at speeds of 10 MHz.

| S-EPMC7283258 | biostudies-literature

Comparison of retina specialist preferences regarding spectral-domain and swept-source optical coherence tomography angiography.

Project description:PurposeThe aim of this study was to compare physician preferences regarding the commercially available spectral-domain (SD) optical coherence tomography angiography (OCTA) and swept-source (SS) OCTA prototype device.DesignComparative analysis of diagnostic instruments was performed.Patients and methodsSubjects at the University of Washington Eye Institute and Harborview Medical Center were prospectively recruited and imaged with the Zeiss SD OCTA (HD-5000, Angioplex) and Zeiss SS OCTA (Plex Elite, Everest) devices on the same day. The study included 10 eyes from 10 subjects diagnosed with a retinal/choroidal disease. Deidentified images were compiled into a survey and sent to retina specialists in various countries. The survey presented masked SD and SS images of each eye for each retinal sublayer side by side. Respondents were asked about their image preference and impact on clinical management. A priori and post hoc preferences for SD vs SS were collected.ResultsFifty-four retina specialists responded to the survey. Median years in practice was 3.00 (interquartile range [IQR] 1.50-17.00). At baseline, 23 (48%) physicians owned an OCTA machine. The majority of physician responses showed a preference for the SS over SD OCTA, independent of the retinal pathology shown (n=454 overall responses, 74%). Nevertheless, the majority indicated that both SD and SS would be equally valuable in informing clinical decisions (n=374 overall responses, 61%).ConclusionThese findings indicate that the majority of retina specialists surveyed prefer SS over SD OCTA based on image quality, regardless of the retinal pathology shown. Regarding the clinical utility of each modality, the majority of physicians perceive SD and SS as equally effective.

| S-EPMC5440072 | biostudies-literature

Assessment of Artifacts in Swept-Source Optical Coherence Tomography Angiography for Glaucomatous and Normal Eyes.

Project description:PurposeTo evaluate the frequency of and identify the factors that influence the artifacts of swept-source optical coherence tomography angiography (SS-OCTA) in glaucomatous and normal eyes.MethodsArtifacts of OCTA images of open-angle glaucoma (OAG) and normal subjects were analyzed using SS-OCTA. Univariate and multivariate logistic regression analyses were performed to evaluate the association of age, sex, best-corrected visual acuity, axial length (AL), intraocular pressure, presence and severity of OAG, and image quality score (IQS) with the presence of artifacts.ResultsImages from 4426 subjects were included in the study. At least one type of artifact was present in 24.54% of the images. The most common artifacts were occurrence of motion (705 eyes, 15.93%), followed by defocus (628 eyes, 14.19%), decentration (134 eyes, 3.03%), masking (62 eyes,1.40%), and segmentation errors (23 eyes, 0.52%). Multivariate logistic analyses showed that the presence of OAG (odds ratio [OR] = 2.71; 95% confidence interval [CI], 2.09-3.51; P < 0.001), female sex (OR = 1.34; 95% CI, 1.12-1.61; P = 0.001), longer AL (OR = 1.09; 95% CI, 1.02-1.17; P = 0.017), and IQS < 40 (OR = 3.75; 95% CI, 3.15-4.48; P < 0.001) were significantly associated with higher odds for the presence of any artifact. The IQS had poor performance for detecting artifacts, with an area under the curve of 0.723, sensitivity of 73.04%, and specificity of 62.53%.ConclusionsOAG eyes had more SS-OCTA image artifacts than normal eyes. IQS is an imperfect tool for identifying artifacts.Translational relevanceSpecial attention should be paid to the effect of artifacts when using SS-OCTA in the clinical setting to assess vascular parameters in patients with glaucoma.

| S-EPMC8764211 | biostudies-literature

Swept-source optical coherence tomography angiography of retinal occlusive vasculitis following brolucizumab administration: a case report.

Project description:BackgroundWe present a case of retinal occlusive vasculitis following brolucizumab administration and the first report of optical coherence tomography angiography (OCTA) findings after treatment.Case presentationA 71-year-old man complained of vision loss in the left eye 6 weeks after brolucizumab injection. His visual acuity was counting fingers, and examination revealed 1 + anterior chamber cells with 2 + vitreous cells. Fundus examination demonstrated vitreous haze, retinal whitening, and vascular sheathing. Fluorescein angiography revealed filling defects in the retinal arteries and veins, and OCTA showed extensive capillary nonperfusion. Under the diagnosis of brolucizumab-associated intraocular inflammation (IOI) and retinal occlusive vasculitis, topical, sub-Tenon, and systemic corticosteroids were administered. After the treatment, visual acuity improved to 20/200, and OCTA revealed gradual improvement in capillary dropout; however, with the limited improvement of reperfusion in the perifoveal areas.ConclusionsPrompt evaluation and intensive corticosteroid treatments are required for brolucizumab-associated IOI. OCTA imaging provides detailed information on microvascular changes in the retinal vascular plexuses in brolucizumab-associated retinal occlusive vasculitis.

| S-EPMC9164534 | biostudies-literature

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