Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

Amplitude decorrelation measurement is sensitive to transverse flow and immune to phase noise in comparison to Doppler and other phase-based approaches. However, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio (SNR) of flow detection. The full OCT spectrum was split into several narrower bands. Inter-B-scan decorrelation was computed using the spectral bands separately and then averaged. The SSADA algorithm was tested on in vivo images of the human macula and optic nerve head. It significantly improved both SNR for flow detection and connectivity of microvascular network when compared to other amplitude-decorrelation algorithms.National Institutes of Health (U.S.) (Grant R01 EY013516)National Institutes of Health (U.S.) (Grant R01-EY11289-26)United States. Air Force Office of Scientific Research (FA9550-10-1-0551

Identifying characteristic features of the retinal and choroidal vasculature in choroideremia using optical coherence tomography angiography

PURPOSE: Using optical coherence tomography angiography (OCTA) to investigate the area with flow in the superficial retinal vessel network (SVRN) and choriocapillaris (CC) layer among male subjects with choroideremia (CHM), female carriers, and normal controls to identify vascular changes. PATIENTS AND METHODS: Images of SRVN and CC layer were acquired in 9 affected males, 5 female carriers, and 14 age- and gender-matched controls using the Angiovue software of the RTVue XR Avanti. RESULTS: The mean age was 33 years for affected male CHM patients (median 30 years), 46 years for female carriers (median 53 years), and 39 years for controls (median 38.5). Mean SRVN area±SD in subjects with CHM was 12.93±2.06 mm², in carrier subjects 15.36±0.60 mm², and in controls 15.30±1.35 mm² (P<0.01). The mean CC area±SD with flow was 6.97±5.26 mm² in CHM subjects, 21.65±0.17 mm² in carriers and 21.36±0.76 mm² in controls (P<0.01). SRVN and CC area with flow showed a negative correlation in CHM subjects with the age (r=−0.86; P<0.003 and r=−0.77; P<0.01, respectively). CC area with flow had a positive correlation with SRVN (r=0.83, P<0.001). Overall, visual acuity had a negative correlation with SRVN and CC area with flow (r=−0.67, P<0.001 and r=−0.57, P<0.002, respectively). CONCLUSIONS: This is the first study to highlight changes in the SRVN in CHM subjects. OCTA detected a reduced area with flow in both retinal and choroidal circulations, and may be a useful tool for monitoring natural history and disease progression in forthcoming clinical trials

Ultrahigh-Speed, Swept-Source Optical Coherence Tomography Angiography in Nonexudative Age-Related Macular Degeneration with Geographic Atrophy

PURPOSE: To investigate ultrahigh speed, swept source optical coherence tomography (SSOCT) angiography for visualizing vascular changes in eyes with non-exudative age-related macular degeneration (AMD) with geographic atrophy (GA). DESIGN: Observational, prospective, cross-sectional study. PARTICIPANTS: A total of 63 eyes from 32 normal subjects and 12 eyes from 7 patients with non-exudative AMD with GA. METHODS: 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 non-exudative AMD with GA. OCTA using variable interscan time analysis (VISTA) was performed to assess CC alteration and differentiate varying degrees of CC flow impairment. MAIN OUTCOME MEASURES: Qualitative comparison of retinal and CC vasculatures in normal subjects versus those in patients with a clinical diagnosis of non-exudative AMD with GA. RESULTS: 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. CONCLUSIONS: The ability of ultrahigh speed, swept source OCTA to visualize alterations in the retinal and CC vasculatures noninvasively makes it a promising tool for assessing non-exudative AMD with GA. OCTA 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

Multiwavelength Observation Campaign of the TeV Gamma-Ray Binary HESS J0632 + 057 with NuSTAR, VERITAS, MDM, and Swift

HESS J0632+057 belongs to a rare subclass of binary systems that emit gamma rays above 100 GeV. It stands out for its distinctive high-energy light curve, which features a sharp “primary” peak and broader “secondary” peak. We present the results of contemporaneous observations by NuSTAR and VERITAS during the secondary peak between 2019 December and 2020 February, when the orbital phase (ϕ) is between 0.55 and 0.75. NuSTAR detected X-ray spectral evolution, while VERITAS detected TeV emission. We fit a leptonic wind-collision model to the multiwavelength spectra data obtained over the four NuSTAR and VERITAS observations, constraining the pulsar spin-down luminosity and the magnetization parameter at the shock. Despite long-term monitoring of the source from 2019 October to 2020 March, the MDM observatory did not detect significant variation in Hα and Hβ line equivalent widths, an expected signature of Be-disk interaction with the pulsar. Furthermore, fitting folded Swift-XRT light-curve data with an intrabinary shock model constrained the orbital parameters, suggesting two orbital phases (at ϕ $_{D}$ = 0.13 and 0.37), where the pulsar crosses the Be-disk, as well as phases for the periastron (ϕ $_{0}$ = 0.30) and inferior conjunction (ϕ $_{IFC}$ = 0.75). The broadband X-ray spectra with Swift-XRT and NuSTAR allowed us to measure a higher neutral hydrogen column density at one of the predicted disk-passing phases

OCT-Based Velocimetry for Blood Flow Quantification

Current clinically available OCTA imaging methods are able to reliably distinguish retinal regions of significant flow from static tissue by evaluating the backscattered OCT signal from repeated measurements. By accurately controlling time delay and position offset between repeated acquisitions, quantitative OCT-based measurements of the underlying blood flow velocity and flow rate are additionally enabled. Multiple methods have been developed for this purpose that operate either on phase, amplitude, or the complex OCT signal and, accordingly, build on different physical models for interpreting the OCT signal modulation arising from moving red blood cells. Here, we present an overview of the technical background of OCT-based methods for quantitative velocimetry, describe their application for retinal imaging in vivo, and discuss their potential and limitations for future clinical ophthalmic applications