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.

/pdf/split-spectrum-amplitude-decorrelation-angiography-with-5066x1kwi2.pdf

Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

Importance The retinal vasculature is involved in many ocular diseases that cause visual loss. Although fluorescein angiography is the criterion standard for evaluating the retina vasculature, it has risks of adverse effects and known defects in imaging all the layers of the retinal vasculature. Optical coherence tomography (OCT) angiography can image vessels based on flow characteristics and may provide improved information. Objective To investigate the ability of OCT angiography to image the vascular layers within the retina compared with conventional fluorescein angiography. Design, Setting, and Participants In this study, performed from March 14, 2014, through June 24, 2014, a total of 5 consecutive, overlapping B-scan OCT angiography images composed of 216 A-scans were obtained at 216 discrete positions within a region of interest, typically a 2 × 2-mm area of the retina. The flow imaging was based on split-spectrum amplitude decorrelation angiography (SSADA), which can dissect layers of vessels in the retina. These distinct layers were compared with the fluorescein angiograms in 12 healthy eyes from patients at a private practice retina clinic to evaluate the ability to visualize the radial peripapillary capillary network. The proportion of the inner vs outer retinal vascular layers was estimated by 3 masked readers and compared with conventional fluorescein angiograms of the same eyes. Main Outcomes and Measures Outcome measures were visualization of the radial peripapillary capillary network in the fluorescein and SSADA scans and the proportion of the inner retinal vascular plexus vs the outer retinal capillary plexus as seen in SSADA scans that would match the fluorescein angiogram. Results In none of the 12 eyes could the radial peripapillary capillary network be visualized completely around the nerve head by fluorescein angiography, whereas the network was readily visualized in the SSADA scans. The fluorescein angiograms were matched, with a mean proportion of the inner vascular plexus being 95.3% (95% CI, 92.2%-97.8%) vs 4.7% (95% CI, 2.6%-5.7%) for the outer capillary plexus from the SSADA scans. Conclusions and Relevance Fluorescein angiography does not image the radial peripapillary or the deep capillary networks well. However, OCT angiography can image all layers of the retinal vasculature without dye injection. Therefore, OCT angiography, and the findings generated, have the potential to affect clinical evaluation of the retina in healthy patients and patients with disease.

https://jamanetwork.com/journals/jamaophthalmology/articlepdf/1910581/eoi140088.pdf

Retinal Vascular Layers Imaged by Fluorescein Angiography and Optical Coherence Tomography Angiography

Microneedles for drug and vaccine delivery.

Quantitative Optical Coherence Tomography Angiography of Choroidal Neovascularization in Age-Related Macular Degeneration

Correlation mapping optical coherence tomography (cmOCT) is a recently proposed technique that extends the capabilities of OCT to enable mapping of vasculature networks. The technique is achieved as a processing step on OCT intensity images that does not require any modification to existing OCT hardware. In this paper we apply the cmOCT processing technique to in vivo human imaging of the volar forearm. We illustrate that cmOCT can produce maps of the microcirculation that clearly follow the accepted anatomical structure. We demonstrate that the technique can extract parameters such as capillary density and vessel diameter. These parameters are key clinical markers for the early changes associated with microvascular diseases. Overall the presented results show that cmOCT is a powerful new tool that generates microcirculation maps in a safe non-invasive, non-contact technique which has clear clinical applications.

In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT).

The use of laser Doppler perfusion imaging LDPI and laser speckle perfusion imaging LSPI is well known in the noninvasive investigation of microcirculatory blood flow. This work compares the two techniques with the recently developed tissue viability TiVi im- aging system, which is proposed as a useful tool to quantify red blood cell concentration in microcirculation. Three systems are evaluated with common skin tests such as the use of vasodilating and vasocon- stricting drugs methlynicotinate and clobetasol, respectively and a reactive hyperaemia maneuver using a sphygmomanometer. The de- vices investigated are the laser Doppler line scanner LDLS, the laser speckle perfusion imager FLPI—both from Moor Instruments Axminster, United Kingdom—and the TiVi imaging system Wheels- Bridge AB, Linkoping, Sweden. Both imaging and point scanning by the devices are used to quantify the provoked reactions. Perfusion images of vasodilatation and vasoconstriction are acquired with both LDLS and FLPI, while TiVi images are acquired with the TiVi imager. Time acquisitions of an averaged region of interest are acquired for temporal studies such as the reactive hyperaemia. In contrast to the change in perfusion over time with pressure, the TiVi imager shows a different response due its measurement of blood concentration rather than perfusion. The responses can be explained by physiological un- derstanding. Although the three devices sample different compart- ments of tissue, and output essentially different variables, comparisons can be seen between the three systems. The LDLS system proves to be suited to measurement of perfusion in deeper vessels, while FLPI and TiVi showed sensitivity to more superficial nutritional supply. LDLS and FLPI are insensitive to the action of the vasoconstrictor, while TiVi shows the clear boundaries of the reaction. Assessment of the reso- lution, penetration depth, and acquisition rate of each instrument show complimentary features that should be taken into account when choosing a system for a particular clinical measurement. © 2009 Society

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-14/issue-3/034025/Comparison-of-instruments-for-investigation-of-microcirculatory-blood-flow-and/10.1117/1.3149863.pdf

Comparison of instruments for investigation of microcirculatory blood flow and red blood cell concentration

Standard optical coherence tomography (OCT) in combination with software tools can be harnessed to generate vascular maps in vivo. In this study we have successfully combined a software algorithm based on correlation statistic to reveal microcirculation morphology on OCT intensity images of a mouse brain in vivo captured trans-cranially and through a cranial window. We were able to estimate vessel geometry at bifurcation as well as along vessel segments down-to mean diameters of about 24 μm. Our technique has potential applications in cardiovascular-related parameter measurements such as volumetric flow as well as in assessing vascular density of normal and diseased tissue.

Correlation mapping method for generating microcirculation morphology from optical coherence tomography (OCT) intensity images.

The use of microneedles as a method of circumventing the barrier properties of the stratum corneum is receiving much attention. Although skin disruption technologies and subsequent transdermal diffusion rates are being extensively studied, no accurate data on depth and closure kinetics of microneedle-induced skin pores are available, primarily due to the cumbersome techniques currently required for skin analysis. We report on the first use of optical coherence tomography technology to image microneedle penetration in real time and in vivo. We show that optical coherence tomography (OCT) can be used to painlessly measure stratum corneum and epidermis thickness, as well as microneedle penetration depth after microneedle insertion. Since OCT is a real-time, in-vivo, nondestructive technique, we also analyze skin healing characteristics and present quantitative data on micropore closure rate. Two locations (the volar forearm and dorsal aspect of the fingertip) have been assessed as suitable candidates for microneedle administration. The results illustrate the applicability of OCT analysis as a tool for microneedle-related skin characterization.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-15/issue-04/046001/In-vivo-dynamic-characterization-of-microneedle-skin-penetration-using-optical/10.1117/1.3463002.pdf

Joey Enfield

Papers

In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT).

Comparison of instruments for investigation of microcirculatory blood flow and red blood cell concentration

Correlation mapping method for generating microcirculation morphology from optical coherence tomography (OCT) intensity images.

In-vivo dynamic characterization of microneedle skin penetration using optical coherence tomography.

Biophotonic methods in microcirculation imaging