Enhanced depth imaging spectral-domain 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.

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Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

Optical coherence tomography angiography.

We demonstrate the depth-resolved and detailed ocular perfusion maps within retina and choroid can be obtained from an ultrahigh sensitive optical microangiography (OMAG). As opposed to the conventional OMAG, we apply the OMAG algorithm along the slow scanning axis to achieve the ultrahigh sensitive imaging to the slow flows within capillaries. We use an 840 nm system operating at an imaging rate of 400 frames∕s that requires 3 s to complete one 3D scan of ∼3×3 mm2 area on retina. We show the superior imaging performance of OMAG to provide functional images of capillary level microcirculation at different land-marked depths within retina and choroid that correlate well with the standard retinal pathology.

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Depth-resolved imaging of capillary networks in retina and choroid using ultrahigh sensitive optical microangiography

In this paper, we demonstrate for the first time that the detailed cutaneous blood flow at capillary level within dermis of human skin can be imaged by optical micro-angiography (OMAG) technique. A novel scanning protocol, i.e. fast B scan mode is used to achieve the capillary flow imaging. We employ a 1310nm system to scan the skin tissue at an imaging rate of 300 frames per second, which requires only ~5 sec to complete one 3D imaging of capillary blood flow within skin. The technique is sensitive enough to image the very slow blood flows at ~4 microm/sec. The promising results show a great potential of OMAG's role in the diagnosis, treatment and management of human skin diseases.

Ultrahigh sensitive optical microangiography for in vivo imaging of microcirculations within human skin tissue beds.

Optical micro-angiography (OMAG), based on Fourier domain optical coherence tomography (OCT), is a recently developed imaging modality that provides dynamic blood flow imaging within microcirculation tissue beds in vivo. This paper presents its first application in imaging the blood circulations in posterior chamber of human eye. To eliminate/minimize the motion artifacts in OMAG flow image caused by the inevitable subject movement, we describe a method to compensate the bulk tissue motion by use of phase changes in sequential OCT A scan signals. By use of a fast OMAG/OCT imaging system at ~840nm wavelength band, we show that OMAG is capable of providing volumetric vasculatural images in retina and choroids, down to capillary level imaging resolution, within approximately 10 s. The depth-resolved volumetric views of the separate retina and choroid vasculatures are also presented. In the end of this paper, we provide a comparison of the OMAG results with those from Doppler OCT and optical coherence angiography.

In vivo volumetric imaging of vascular perfusion within human retina and choroids with optical micro-angiography.

Importance Quantitative measurements based on optical coherence tomographic angiography (OCTA) may have value in managing diabetic retinopathy (DR), but there is limited information on the ability of OCTA to distinguish eyes with DR. Objective To evaluate the ability of measurements of retinal microvasculature using OCTA to distinguish healthy eyes from eyes with DR. Design, Setting, and Participants In this prospective cross-sectional study, OCTA was used to examine the eyes of participants with type 2 diabetes with or without DR and the eyes of participants without diabetes from September 17, 2015, to April 6, 2016. Density maps based on superficial retinal layer (SRL) and deeper retinal layer (DRL) images were generated after a method to remove decorrelation tails was applied to the DRL images. Exposures Both eyes of each participant were examined by means of a 3-mm OCTA scan and 7-field fundus photography using the Diabetic Retinopathy Severity Scale. Main Outcomes and Measures Two measures were examined: perfusion density, based on the area of vessels, and vessel density, based on a map with vessels of 1-pixel width. The size of the foveal avascular zone was also calculated automatically, and so was the area under the receiver operating characteristic curve. Results A total of 50 eyes from 26 participants with diabetes (10 women and 16 men; mean [SD] age, 64.9 [7.5] years) and 50 healthy eyes from 25 participants without diabetes (14 women and 11 men; mean [SD] age, 64.0 [7.1] years) were imaged. All participants were white. Vessel density measured in the SRL had the highest area under the receiver operating characteristic curve (0.893 [95% CI, 0.827-0.959]), compared with perfusion density in the SRL (0.794 [95% CI, 0.707-0.881]), foveal avascular zone area (0.472 [95% CI, 0.356-0.588]), and vessel density in the DRL (0.703 [95% CI, 0.601-0.805]). Vessel density in the SRL negatively correlated with best-corrected visual acuity ( r  = –0.28; P  = .05) and severity of DR ( r  = –0.46; P  = .001). Density metrics correlated with age. No correlation was detected between vascular density or foveal avascular zone metrics and hemoglobin A 1C or duration of diabetes. Conclusions and Relevance Vessel density measured by OCTA provides a quantitative metric of capillary closure that correlates with severity of DR and may allow staging, diagnosis, and monitoring that do not require subjective evaluation of fundus images.

Quantification of Retinal Microvascular Density in Optical Coherence Tomographic Angiography Images in Diabetic Retinopathy.

We propose a Doppler optical micro-angiography (DOMAG) method to image flow velocities of the blood flowing in functional vessels within microcirculatory tissue beds in vivo. The method takes the advantages of recently developed optical micro-angiography (OMAG) technology, in which the endogenous optical signals backscattered from the moving blood cells are isolated from those originated from the tissue background, i.e., the tissue microstructures. The phase difference between adjacent A scans of OMAG flow signals is used to evaluate the flow velocity, similar to phase-resolved Doppler optical coherence tomography (PRDOCT). To meet the requirement of correlation between adjacent A scans in using the phase resolved technique to evaluate flow velocity, an ideal tissue-sample background (i.e., optically homogeneous tissue sample) is digitally reconstructed to replace the signals that represent the heterogeneous features of the static sample that are rejected in the OMAG flow images. Because of the ideal optical-homogeneous sample, DOMAG is free from the characteristic texture pattern noise due to the heterogeneous property of sample, leading to dramatic improvement of the imaging performance. A series of phantom flow experiments are performed to evaluate quantitatively the improved imaging performance. We then conduct in vivo experiments on a mouse brain to demonstrate that DOMAG is capable of quantifying the flow velocities within cerebrovascular network, down to capillary level resolution. Finally, we compare the in vivo imaging performance of DOMAG with that of PRDOCT, and show that DOMAG delivers at least 15-fold increase over the PRDOCT method in terms of the lower limit of flow velocity that can be detected.

Lin An

Papers

Depth-resolved imaging of capillary networks in retina and choroid using ultrahigh sensitive optical microangiography

Ultrahigh sensitive optical microangiography for in vivo imaging of microcirculations within human skin tissue beds.

In vivo volumetric imaging of vascular perfusion within human retina and choroids with optical micro-angiography.

Quantification of Retinal Microvascular Density in Optical Coherence Tomographic Angiography Images in Diabetic Retinopathy.

Doppler optical micro-angiography for volumetric imaging of vascular perfusion in vivo