To investigate the application of optical microangiography (OMAG) in living human eye. Patients with different macular diseases were recruited, including diabetic retinopathy (DR), geographic atrophy (GA), retinitis pigmentosa (RP), and venous occlusion, et al. Wide field OCT angiography images can be generated by montage scanning protocol based on the tracking system. OMAG algorithm based on complex differentiation was used to extract the blood flow and removed the bulk motion by 2D cross-correlation method. The 3D angiography was segmented into 3 layers in the retina and 2 layers in the choroid. The en-face maximum projection was used to obtain 2-dimensional angiograms of different layers coded with different colors. Flow and structure images were combined for cross-sectional view. En face OMAG images of different macular diseases showed a great agreement with FA. Meanwhile, OMAG gave more distinct vascular network visions that were less affected by hemorrhage and leakage. The MAs were observed in both superficial and middle retinal layers based on OMAG angiograms in different layers of DR patients. The contour line of FAZ was extracted as well, which can be quantitative the retinal diseases. For GA patient, the damage of RPE layer enhanced the penetration of light and enabled the acquisition of choriocapillaries and choroidal vessels. The wide field OMAG angiogram enabled the capability of capturing the entire geographic atrophy. OMAG provides depth-resolved information and detailed vascular images of DR and GA patients, providing a better visualization of vascular network compared to FA.
Optical coherence tomography (OCT)-based angiography is increasingly becoming a clinically useful and important imaging technique due to its ability to provide volumetric microvascular networks innervating tissue beds in vivo without a need for exogenous contrast agent. Numerous OCT angiography algorithms have recently been proposed for the purpose of contrasting microvascular networks. A general literature review is provided on the recent progress of OCT angiography methods and algorithms. The basic physics and mathematics behind each method together with its contrast mechanism are described. Potential directions for future technical development of OCT based angiography is then briefly discussed. Finally, by the use of clinical data captured from normal and pathological subjects, the imaging performance of vascular networks delivered by the most recently reported algorithms is evaluated and compared, including optical microangiography, speckle variance, phase variance, split-spectrum amplitude decorrelation angiography, and correlation mapping. It is found that the method that utilizes complex OCT signal to contrast retinal blood flow delivers the best performance among all the algorithms in terms of image contrast and vessel connectivity. The purpose of this review is to help readers understand and select appropriate OCT angiography algorithm for use in specific applications.
KEYWORDS: Graphene, Fiber Bragg gratings, Sensors, Reflection, Chemical analysis, Gas sensors, Refractive index, Adsorption, Biological and chemical sensing, Signal attenuation
In this paper, a novel graphene-coated microfiber Bragg grating (GMFBG) sensor is proposed and demonstrated for detection of gas concentration, for the first time. Taking advantage of the surface field enhancement and polar molecular adsorption by the graphene film, we find that this structure is very sensitive to local chemical gas concentration, and the obtained sensitivities are 0.2 and 0.5ppm for NH3 and Xylene gas for tiny gas variation, respectively. Such a miniature GMFBG sensor could find applications in biological or chemical sensing, such as for trace analysis.
A high sensitivity NH3 gas sensor based on graphene/microfiber hybrid waveguide (GMHW) is reported for the first time. Enhanced by the graphene, a very high sensitivity of 0.3ppm is achieved for GMHW-based NH3 gas sensing. This work may open a window for development of novel GMHW-based gas sensors with high sensitivity, small footprint, easy fabrication and low cost.
Interstitial near-infrared laser thermal therapy (LITT) is currently undergoing clinical trials as an alternative to watchful waiting or radical surgery in patients with low-risk focal prostate cancer. Currently, we use magnetic resonance image (MRI)-based thermography to monitor treatment delivery and determine indirectly the completeness of the target tissue destruction while avoiding damage to adjacent normal tissues, particularly the rectal wall. However, incomplete tumor destruction has occurred in a significant fraction of patients due to premature termination of treatment, since the photocoagulation zone is not directly observed. Hence, we are developing transrectal diffuse optical tomography (TRDOT), in combination with transrectal 3D ultrasound (3D-TRUS), to address his limitation. This is based on the large changes in optical scattering expected upon tissue coagulation. Here, we present forward simulations of a growing coagulated lesion with optical scattering contrast, using an established finite element analysis software platform (NIRFAST). The simulations were validated in tissue-simulating phantoms, with measurements acquired by a state-of-the-art continuous wave (CW) TRDOT system and a recently assembled bench-top CW-DOT system, with specific source-detector configurations. Two image reconstruction schemes were investigated and evaluated, specifically for the accurate delineation of the posterior boundary of the coagulation zone as the critical parameter for treatment guidance in this clinical application.
The normalized Born ratio of steady-state fluorescence measurements in a concave or convex-shaped medium geometry is investigated by analytical and numerical methods. The “concave” geometry refers to a scattering-dominant medium enclosed by a long circular cylindrical applicator, and the “convex” geometry refers to a scattering-dominant medium enclosing a long circular cylindrical applicator. The numerical investigation uses finite element- method, and the corresponding analytical evaluation is based upon a recently developed method of treating steady-state photon diffusion in both concave and convex geometries. The steady-state Born ratio associated with a source and a detector located on the medium-applicator interface is examined for the medium to have a homogeneous distribution of fluorophore, and for the source and detector aligning either azimuthally or longitudinally in both concave and convex geometries. At a given set of optical properties and the line-of-sight source-detector distance, the normalized Born ratio is always smaller in concave and greater in convex geometry respectively when comparing to that in semi-infinite geometry. At a given set of optical properties, the rate of increase of the normalized Born ratio versus the line-of-sight source-detector distance is the greatest along the azimuthal direction in convex geometry among the studied cases. The change of the normalized Born ratio caused by containing a target of either positive or negative contrast of fluorophore in the otherwise homogeneous background of fluorophore is also investigated numerically. The results for both homogenous and heterogeneous fluorophore distribution demonstrate that the normalized Born ratio is a geometry-specific parameter that imposes geometrically-specific sensitivity in measurements.
We predict the phenomenon of "spiral-planar equivalence" for steady-state photon diffusion associated with a cylindrical
applicator. Recently we have derived a unified theory of steady-state photon diffusion in a homogenous medium
bounded either externally (referred to as a concave geometry) or internally (referred to as a convex geometry) by an
infinitely long circular cylindrical applicator [JOSAA, 27(3): 648-662 (2010)]. Despite the idealization of the geometry
by assuming an infinite length of the applicator, the analytic prediction withholds the quantitative examinations based on
experimental measurements, and finite-element solution of photon diffusion. An interesting finding is that the decay of
photon fluence in a concave boundary is smaller in the azimuth direction but greater along the longitudinal direction, in
comparison with that in a semi-infinite geometry along a straight line, for the same line-of-sight distance between the
source and the detector. Conversely, the decay of photon fluence in a convex boundary is greater in the azimuth direction
but smaller along the longitudinal direction, in comparison with that in a semi-infinite geometry along a straight line, for
the same line-of-sight source-detector distance. These findings suggest that on the cylindrical applicator interface there
should exist a spiral direction (oblique to both the azimuthal and longitudinal directions), along which the rate of photon
fluence decay follows that along a straight line on a planar semi-infinite interface---which is called the "spiral-planar
equivalence". The "spiral-planar equivalence" is derivable analytically, and subject to quantitative evaluations.
Validating the "spiral-planar equivalence" not only enriches the understanding of photon diffusion in cylindricalinterface
geometry, but also provides unique semi-infinite-based imaging application in trans-lumenal diffuse optical
sensing. The "spiral-planar equivalence" may be applicable to time-resolved photon-diffusion.
The geometry of trans-lumenal diffuse optical measurement is considerably different from that of externally applied
diffuse optical imaging. In externally-applied diffuse optical imaging of breast, brain, etc, an analytic solution to
the diffusion equation for a planar semi-infinite medium is often applied. This solution works accurately for planar
applicator and is a good approximation for a ring applicator of considerable size. In trans-lumenal diffuse optical
imaging of internal organs like the prostate, the applicator likely should have a convex surface profile for interfacing
with a typically circular cross-section of the lumen. The influence of this convex applicator shape upon the photon
transport is expected to cause a deviation from the solution predicted by a semi-infinite planar boundary. This
interference, if available, is particularly relevant to the axial geometry in trans-lumenal diffuse optical imaging. This
work investigates the analytic solution of continuous-wave photon diffusion equation for axial imaging when a
cylindrical trans-lumenal applicator is used. The Green's function of the photon diffusion equation in an infinite medium
geometry is expanded in cylindrical coordinates, and an image-source method is utilized to derive the analytic solution
for circular concave & circular convex boundary profiles based on extrapolated boundary condition. Numerical
evaluations are conducted to examine the effect of the circular boundary. Empirical solution potentially useful for
calibrating the photon remission data in a circular boundary is also derived. The numerical evaluation results and the
empirical solution are subject to validation against Monte Carlo simulations and experimental measurements.
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