Anqi Zhang - Academia.edu (original) (raw)

Papers by Anqi Zhang

Ophthalmology retina

To visualize and quantify the size and vessel density of macular neovascularization (MNV) using o... more To visualize and quantify the size and vessel density of macular neovascularization (MNV) using optical coherence tomography angiography (OCTA) with a projection artifact removal algorithm. Multicenter, observational study. Subjects with MNV in at least one eye. Patients were imaged using either a swept-source OCT angiography (SS-OCTA) prototype system or a spectral-domain OCT angiography (SD-OCTA) prototype system. The optical microangiography (OMAG) algorithm was used to generate the OCTA images. Projection artifacts from the overlying retinal circulation were removed from the OMAG OCTA images using a novel algorithm. Following removal of the projection artifacts from the OCTA images, we assessed the size and vascularity of the MNV. Concurrent fluorescein angiography (FA) and indocyanine green angiography (ICGA) images were used to validate the artifact-free OMAG images whenever available. Size and vascularity of MNV imaged with OCTA before and after the use of a projection-artifa...

Biomedical Optics Express, 2015

Current optical coherence tomography (OCT) based microangiography is prone to noise that arises f... more Current optical coherence tomography (OCT) based microangiography is prone to noise that arises from static background. This work presents a novel feature space based optical micro-angiography (OMAG) method (fsOMAG) that can effectively differentiate flow signal from static background in the feature space. fsOMAG consists of two steps. In the first step a classification map is generated that provides criterion for classification in the second step to extract functional blood flow from experimental data set. The performance of fsOMAG is examined through phantom experiments and in-vivo human retinal imaging, and compared with the existing OMAG. The results indicate its potential for clinical applications.

Optics Letters, 2014

We present a novel design for an endoscopic imaging catheter utilizing diffractive optics for ult... more We present a novel design for an endoscopic imaging catheter utilizing diffractive optics for ultrahigh resolution optical coherence tomography (OCT) imaging at 800 nm. A diffractive microlens was developed to alleviate severe chromatic aberration when a broadband light source was employed at the 800 nm wavelength range. Combined with a home-built fiber rotary joint and a broadband Ti:sapphire laser, the imaging catheter achieved a lateral resolution of 6.2 μm and an axial resolution of 3.0 μm in air. The performance of the catheter was demonstrated by threedimensional-fullcircumferential endoscopic OCT imaging of guinea pig esophagus in vivo. Optical coherence tomography (OCT) is a noninvasive imaging technology capable of assessing tissue micro-anatomy with micrometer-scale resolution and a few millimeters of imaging depth. Miniature imaging catheters/endoscopes are a critical component of OCT technology for enabling translational imaging of internal luminal organs, such as the gastrointestinal tract or airways. Most OCT catheters/endoscopes that have been developed so far were designed for working at the wavelength around 1300 nm, which provides an excellent axial resolution of about 7-20 μm and an imaging depth of about 2-3 mm [1-7]. A higher resolution is highly desired in order to resolve fine tissue structures such as airway smooth muscle, intestinal crypts, and structural changes associated with early stage diseases. Considering the quadratic dependence of the axial resolution on the center wavelength λ c of the OCT light source (i.e., δz ∝ /Δλ, where Δλ is the 3 dB bandwidth of the source spectrum), it would be more convenient to achieve an ultrahigh axial resolution with a broadband light source at 800 nm compared to 1300 nm. In addition, an 800 nm source could also potentially provide improved image contrast owing to the increased light

Biomedical Optics Express, 2015

Current optical coherence tomography (OCT) based microangiography is prone to a projection (or ta... more Current optical coherence tomography (OCT) based microangiography is prone to a projection (or tailing) effect due to the high scattering property of blood within overlying patent vessels, creating artifacts that interfere with the interpretation of retinal angiographic results. In this work, the projection effect in OCT micro-angiography is examined and its causality is explained by strong light scattering and photon propagation within blood. A simple practical approach is then introduced to minimize these artifacts presented in the outer retinal avascular space, especially useful for examining clinical cases with choroidal neovascularization (CNV). Demonstrated through in-vivo human posterior eye imaging of healthy and CNV subjects, the proposed method is shown effective to eliminate the projection artifacts in outer retinal space of OCT micro-angiography, resulting in better visualization of the pathological neovascularization when compared with the current common approaches. In addition, it is also shown that the proposed method is applicable to minimize the projection artifacts appearing in deep retinal layers.

Optics letters, 2014

We present a generic phase-domain processing method for detecting speckles in Fourier-domain opti... more We present a generic phase-domain processing method for detecting speckles in Fourier-domain optical coherence tomography (OCT) images. The physics behind the interferometry is revisited and analytically along with simulation results it indicates that the speckle formation comes with phase distortion to the complex OCT signal. The first and the second derivatives of phase along the imaging depth are then calculated for speckle identification. The phase-domain processing method was applied to images acquired by both spectral-domain OCT and swept-source OCT systems, and the experimental results show that this method enables pixel-wise speckle identification.

Journal of biomedical optics, 2015

Optical coherence tomography (OCT)-based angiography is increasingly becoming a clinically useful... more 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-spectru...

introduced this splendid field to me. During my more than four year's Ph.D. study, Dr. Piao guide... more introduced this splendid field to me. During my more than four year's Ph.D. study, Dr. Piao guides me through my stumbling learning progress and helps me overcome every pitfall during my study. His persistent enthusiasm for knowledge has kept me engaged for research and made this dissertation possible. His kindness also makes my stay at OSU a cherishable memory. I also need to thank Dr. Charles F. Bunting who inspires me with his personality and way of teaching, not to mention the knowledge of Electromagnetic I learnt from him. I thank Dr. Weili Zhang for his support in my department and Dr. Jiahong Wu especially for his help on my Mathematics. My thanks also extend to my former and current colleagues: Zhen Jiang, Guan Xu, Wei Sun, Yuanyuan Jiang and Sovanlal Mukherjee for their help on my research. Above ground, I am greatly indebted to my father Peiyi Zhang, my mother Yuhua Gao for their never-ending support and my parents in-law Cilin Li and Jinlian Ouyang for their unswervingly love. Finally I want to thank my wife Shan Li, who blesses my life with bright light during every piece of darkness I have encountered.

JAMA ophthalmology, Jan 29, 2015

Acute macular neuroretinopathy (AMN) has been characterized as wedge-shaped superficial retinal d... more Acute macular neuroretinopathy (AMN) has been characterized as wedge-shaped superficial retinal defects in the macula, resulting in paracentral scotomas. AMN has been associated with vasoconstrictors and sympathomimetics. 1 In 2013, paracentral acute middle maculopathy (PAMM) was described as an AMN variant, seen as a hyperreflective band involving the middle retinal layers on spectral-domain optical coherence tomography (SD-OCT). 1 Type 1 PAMM lesions involve layers above the outer plexiform layer (OPL), reflecting superficial or intermediate capillary plexus occlusion; type 2 lesions involve layers below the OPL, affecting the deep capillary plexus. 1 Macular lesions in AMN/PAMM are best visualized on near-infrared reflectance (NIR) imaging, correlating with SD-OCT OPL hyperreflectivity 2,3 and may be otherwise subclinical. Definitive evidence of the ischemic origin of PAMM has been lacking. Only one case report has demonstrated a transient retinal artery occlusion on fluorescein angiography (FA). 4 OCT angiography (OCT-A) provides novel retinal vascular flow visualization and provides a unique opportunity to visualize the depth of a vascular defect. 5 Here we report the noninvasive ability of OCT-A to visualize a capillary perfusion defect in PAMM/AMN. REPORT OF A CASE A pregnant 29 year-old female at 21 weeks gestational age presented for evaluation of a paracentral scotoma in her right eye. One day prior, she experienced a presyncopal episode after noticing the scotoma. She was treated with intravenous fluids for hypotension (blood pressure: 77/50 mmHg) and was slightly anemic. Besides her pregnancy, she had no other past medical or ocular history. Her only medication was a prenatal vitamin. She denied illicit drug use and excess caffeine consumption.

Optics letters, Jan 15, 2016

Optical coherence tomography angiography (OCTA) has increasingly become clinically important, par... more Optical coherence tomography angiography (OCTA) has increasingly become clinically important, particularly in ophthalmology. However, the field of view (FOV) for current OCTA imaging is severely limited due to A-scan rates that can be afforded by current clinical systems and, more importantly, the requirement of a repeated scanning protocol. This Letter evaluates the possibility of using only two repeated B-scans for OCTA for the purpose of an increased FOV. The effect of repeated numbers on the OCTA result is discussed through experiments on an animal model in vivo and evaluated using quantitative metrics for image quality. Demonstrated through in vivo imaging of a pathological human eye, we show that optical microangiography-based OCTA with two repeated B-scans can provide wide-field angiography up to 12×12 mm with clinically acceptable image quality.

Sovremennye tehnologii v medicine, 2015

The recent development of optical coherence tomography in ophthalmology has shown great interests... more The recent development of optical coherence tomography in ophthalmology has shown great interests in using the system in 1 µm in contrast to 800 nm wavelength range due to the less reflection and absorption of retinal pigment epithelium and pigmented choroidal melanocytes in 1 µm wavelength. The clinical value of using 1 µm system has been demonstrated in choroid imaging, retinal and choroidal microcirculation, etc. By examining different aspects of the posterior eye, the specificity and sensitivity of diagnosis can be increased. On the other hand, higher speed can greatly reduce the measuring time and motion artifacts, which brings comfort to the patients and improves the image quality. In this work, we report a newly developed multifunctional 1050 nm spectral domain optical coherence tomography (SD-OCT) system working at 147 kHz A-scan rate for posterior eye imaging. The uniqueness of this system is: 1) its capability of providing not only simultaneous structural imaging of the complete posterior eye, but also the visualization of the retinal blood vessel network with larger field of view and good image quality compared with former SD-OCT systems; 2) it's fast 147 kHz A-scan rate which has not been reported before. It is demonstrated through in vivo experiments that this system delivers not only superior performance of posterior eye structural imaging but also detailed visualization of microcirculation network in retina. The choroid of the eye with either myopic or normal conditions can clearly be visualized through the entire scanning volume. These results indicate great potential in applying this new system for clinical studies.

Journal of the Optical Society of America A, 2013

As Part V in our series, this paper examines steady-state fluorescence photon diffusion in a homo... more As Part V in our series, this paper examines steady-state fluorescence photon diffusion in a homogenous medium that contains a homogenous distribution of fluorophores, and is enclosed by a "concave" circular cylindrical applicator or is enclosing a "convex" circular cylindrical applicator, both geometries being infinite in the longitudinal dimension. The aim is to predict by analytics and examine with the finite-element method the changing characteristics of the fluorescence-wavelength photon-fluence rate and the ratio (sometimes called the Born ratio) of it versus the excitation-wavelength photon-fluence rate, with respect to the source-detector distance. The analysis is performed for a source and a detector located on the medium-applicator interface and aligned either azimuthally or longitudinally in both concave and convex geometries. When compared to its steady-state counterparts on a semi-infinite medium-applicator interface with the same line-of-sight source-detector distance, the fluorescence-wavelength photon-fluence rate reduces faster along the longitudinal direction and slower along the azimuthal direction in the concave geometry, and conversely in the convex geometry. However, the Born ratio increases slower in both azimuthal and longitudinal directions in the concave geometry and faster in both directions in the convex geometry, respectively, when compared to that in the semi-infinite geometry.

Investigative Opthalmology & Visual Science, 2016

PURPOSE. To investigate the vascular microcirculation changes in the retinal nerve fiber layer (R... more PURPOSE. To investigate the vascular microcirculation changes in the retinal nerve fiber layer (RNFL) in normal, glaucoma suspect, and open-angle glaucoma (OAG) groups using optical coherence tomography-based microangiography (OMAG). METHODS. One eye from each subject was scanned with a Cirrus HD-OCT 5000-based OMAG prototype system montage scanning protocol centered at the optic nerve head (ONH). Blood flow signals were extracted using OMAG algorithm. Retinal nerve fiber layer vascular microcirculation was measured by calculating the blood flux index and vessel area density within a 1.2-mm width annulus centered at the ONH with exclusion of big retinal vessels. One-way ANOVA were performed to analyze the RNFL microcirculation among groups. Linearregression models were constructed to analyze the correlation between RNFL microcirculation and clinical parameters. Discrimination capabilities of the flow metrics were assessed with the area under the receiver operating characteristic curve (AROC). RESULTS. Twenty normal, 26 glaucoma suspect, and 42 OAG subjects were enrolled. Eyes from OAG subjects and glaucoma suspects showed significantly lower blood flux index compared with normal eyes (P 0.0015). Retinal nerve fiber layer blood flow metrics showed significant correlations with visual field indices and structural changes in glaucomatous eyes (P 0.0123). Similar discrimination capability of blood flux index compared with RNFL thickness was found in both disease groups. CONCLUSIONS. Peripapillary RNFL vascular microcirculation measured as blood flux index by OMAG showed significant differences among OAG, glaucoma suspect, and normal controls and was significantly correlated with functional and structural defects. Retinal nerve fiber layer microcirculation measurement using OMAG may help physicians monitor glaucoma.

Scientific reports, Jan 25, 2016

Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal v... more Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal vascular networks without a need for contrast dyes. For sophisticated monitoring and diagnosis of retinal diseases, OCTA capable of providing wide-field and high definition images of retinal vasculature in a single image is desirable. We report OCTA with motion tracking through an auxiliary real-time line scan ophthalmoscope that is clinically feasible to image functional retinal vasculature in patients, with a coverage of more than 60 degrees of retina while still maintaining high definition and resolution. We demonstrate six illustrative cases with unprecedented details of vascular involvement in retinal diseases. In each case, OCTA yields images of the normal and diseased microvasculature at all levels of the retina, with higher resolution than observed with fluorescein angiography. Wide-field OCTA technology will be an important next step in augmenting the utility of OCT technology in...

We demonstrate that, for a long cylindrical applicator that interfaces concavely or convexly with... more We demonstrate that, for a long cylindrical applicator that interfaces concavely or convexly with a scattering-dominant medium, a unique set of spiral-shaped directions exist on the tissue-applicator interface, along which the diffuse photon remission is essentially modeled by the photon remission along a straight line on a semi-infinite interface. This interesting phenomenon, which is validated in steady state in this work by finite-element and Monte Carlo methods, may be particularly useful for simplifying deeper-tissue sensing in endoscopic imaging geometry.

Ophthalmology retina

To visualize and quantify the size and vessel density of macular neovascularization (MNV) using o... more To visualize and quantify the size and vessel density of macular neovascularization (MNV) using optical coherence tomography angiography (OCTA) with a projection artifact removal algorithm. Multicenter, observational study. Subjects with MNV in at least one eye. Patients were imaged using either a swept-source OCT angiography (SS-OCTA) prototype system or a spectral-domain OCT angiography (SD-OCTA) prototype system. The optical microangiography (OMAG) algorithm was used to generate the OCTA images. Projection artifacts from the overlying retinal circulation were removed from the OMAG OCTA images using a novel algorithm. Following removal of the projection artifacts from the OCTA images, we assessed the size and vascularity of the MNV. Concurrent fluorescein angiography (FA) and indocyanine green angiography (ICGA) images were used to validate the artifact-free OMAG images whenever available. Size and vascularity of MNV imaged with OCTA before and after the use of a projection-artifa...

Biomedical Optics Express, 2015

Current optical coherence tomography (OCT) based microangiography is prone to noise that arises f... more Current optical coherence tomography (OCT) based microangiography is prone to noise that arises from static background. This work presents a novel feature space based optical micro-angiography (OMAG) method (fsOMAG) that can effectively differentiate flow signal from static background in the feature space. fsOMAG consists of two steps. In the first step a classification map is generated that provides criterion for classification in the second step to extract functional blood flow from experimental data set. The performance of fsOMAG is examined through phantom experiments and in-vivo human retinal imaging, and compared with the existing OMAG. The results indicate its potential for clinical applications.

Optics Letters, 2014

We present a novel design for an endoscopic imaging catheter utilizing diffractive optics for ult... more We present a novel design for an endoscopic imaging catheter utilizing diffractive optics for ultrahigh resolution optical coherence tomography (OCT) imaging at 800 nm. A diffractive microlens was developed to alleviate severe chromatic aberration when a broadband light source was employed at the 800 nm wavelength range. Combined with a home-built fiber rotary joint and a broadband Ti:sapphire laser, the imaging catheter achieved a lateral resolution of 6.2 μm and an axial resolution of 3.0 μm in air. The performance of the catheter was demonstrated by threedimensional-fullcircumferential endoscopic OCT imaging of guinea pig esophagus in vivo. Optical coherence tomography (OCT) is a noninvasive imaging technology capable of assessing tissue micro-anatomy with micrometer-scale resolution and a few millimeters of imaging depth. Miniature imaging catheters/endoscopes are a critical component of OCT technology for enabling translational imaging of internal luminal organs, such as the gastrointestinal tract or airways. Most OCT catheters/endoscopes that have been developed so far were designed for working at the wavelength around 1300 nm, which provides an excellent axial resolution of about 7-20 μm and an imaging depth of about 2-3 mm [1-7]. A higher resolution is highly desired in order to resolve fine tissue structures such as airway smooth muscle, intestinal crypts, and structural changes associated with early stage diseases. Considering the quadratic dependence of the axial resolution on the center wavelength λ c of the OCT light source (i.e., δz ∝ /Δλ, where Δλ is the 3 dB bandwidth of the source spectrum), it would be more convenient to achieve an ultrahigh axial resolution with a broadband light source at 800 nm compared to 1300 nm. In addition, an 800 nm source could also potentially provide improved image contrast owing to the increased light

Biomedical Optics Express, 2015

Current optical coherence tomography (OCT) based microangiography is prone to a projection (or ta... more Current optical coherence tomography (OCT) based microangiography is prone to a projection (or tailing) effect due to the high scattering property of blood within overlying patent vessels, creating artifacts that interfere with the interpretation of retinal angiographic results. In this work, the projection effect in OCT micro-angiography is examined and its causality is explained by strong light scattering and photon propagation within blood. A simple practical approach is then introduced to minimize these artifacts presented in the outer retinal avascular space, especially useful for examining clinical cases with choroidal neovascularization (CNV). Demonstrated through in-vivo human posterior eye imaging of healthy and CNV subjects, the proposed method is shown effective to eliminate the projection artifacts in outer retinal space of OCT micro-angiography, resulting in better visualization of the pathological neovascularization when compared with the current common approaches. In addition, it is also shown that the proposed method is applicable to minimize the projection artifacts appearing in deep retinal layers.

Optics letters, 2014

We present a generic phase-domain processing method for detecting speckles in Fourier-domain opti... more We present a generic phase-domain processing method for detecting speckles in Fourier-domain optical coherence tomography (OCT) images. The physics behind the interferometry is revisited and analytically along with simulation results it indicates that the speckle formation comes with phase distortion to the complex OCT signal. The first and the second derivatives of phase along the imaging depth are then calculated for speckle identification. The phase-domain processing method was applied to images acquired by both spectral-domain OCT and swept-source OCT systems, and the experimental results show that this method enables pixel-wise speckle identification.

Journal of biomedical optics, 2015

Optical coherence tomography (OCT)-based angiography is increasingly becoming a clinically useful... more 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-spectru...

introduced this splendid field to me. During my more than four year's Ph.D. study, Dr. Piao guide... more introduced this splendid field to me. During my more than four year's Ph.D. study, Dr. Piao guides me through my stumbling learning progress and helps me overcome every pitfall during my study. His persistent enthusiasm for knowledge has kept me engaged for research and made this dissertation possible. His kindness also makes my stay at OSU a cherishable memory. I also need to thank Dr. Charles F. Bunting who inspires me with his personality and way of teaching, not to mention the knowledge of Electromagnetic I learnt from him. I thank Dr. Weili Zhang for his support in my department and Dr. Jiahong Wu especially for his help on my Mathematics. My thanks also extend to my former and current colleagues: Zhen Jiang, Guan Xu, Wei Sun, Yuanyuan Jiang and Sovanlal Mukherjee for their help on my research. Above ground, I am greatly indebted to my father Peiyi Zhang, my mother Yuhua Gao for their never-ending support and my parents in-law Cilin Li and Jinlian Ouyang for their unswervingly love. Finally I want to thank my wife Shan Li, who blesses my life with bright light during every piece of darkness I have encountered.

JAMA ophthalmology, Jan 29, 2015

Acute macular neuroretinopathy (AMN) has been characterized as wedge-shaped superficial retinal d... more Acute macular neuroretinopathy (AMN) has been characterized as wedge-shaped superficial retinal defects in the macula, resulting in paracentral scotomas. AMN has been associated with vasoconstrictors and sympathomimetics. 1 In 2013, paracentral acute middle maculopathy (PAMM) was described as an AMN variant, seen as a hyperreflective band involving the middle retinal layers on spectral-domain optical coherence tomography (SD-OCT). 1 Type 1 PAMM lesions involve layers above the outer plexiform layer (OPL), reflecting superficial or intermediate capillary plexus occlusion; type 2 lesions involve layers below the OPL, affecting the deep capillary plexus. 1 Macular lesions in AMN/PAMM are best visualized on near-infrared reflectance (NIR) imaging, correlating with SD-OCT OPL hyperreflectivity 2,3 and may be otherwise subclinical. Definitive evidence of the ischemic origin of PAMM has been lacking. Only one case report has demonstrated a transient retinal artery occlusion on fluorescein angiography (FA). 4 OCT angiography (OCT-A) provides novel retinal vascular flow visualization and provides a unique opportunity to visualize the depth of a vascular defect. 5 Here we report the noninvasive ability of OCT-A to visualize a capillary perfusion defect in PAMM/AMN. REPORT OF A CASE A pregnant 29 year-old female at 21 weeks gestational age presented for evaluation of a paracentral scotoma in her right eye. One day prior, she experienced a presyncopal episode after noticing the scotoma. She was treated with intravenous fluids for hypotension (blood pressure: 77/50 mmHg) and was slightly anemic. Besides her pregnancy, she had no other past medical or ocular history. Her only medication was a prenatal vitamin. She denied illicit drug use and excess caffeine consumption.

Optics letters, Jan 15, 2016

Optical coherence tomography angiography (OCTA) has increasingly become clinically important, par... more Optical coherence tomography angiography (OCTA) has increasingly become clinically important, particularly in ophthalmology. However, the field of view (FOV) for current OCTA imaging is severely limited due to A-scan rates that can be afforded by current clinical systems and, more importantly, the requirement of a repeated scanning protocol. This Letter evaluates the possibility of using only two repeated B-scans for OCTA for the purpose of an increased FOV. The effect of repeated numbers on the OCTA result is discussed through experiments on an animal model in vivo and evaluated using quantitative metrics for image quality. Demonstrated through in vivo imaging of a pathological human eye, we show that optical microangiography-based OCTA with two repeated B-scans can provide wide-field angiography up to 12×12 mm with clinically acceptable image quality.

Sovremennye tehnologii v medicine, 2015

The recent development of optical coherence tomography in ophthalmology has shown great interests... more The recent development of optical coherence tomography in ophthalmology has shown great interests in using the system in 1 µm in contrast to 800 nm wavelength range due to the less reflection and absorption of retinal pigment epithelium and pigmented choroidal melanocytes in 1 µm wavelength. The clinical value of using 1 µm system has been demonstrated in choroid imaging, retinal and choroidal microcirculation, etc. By examining different aspects of the posterior eye, the specificity and sensitivity of diagnosis can be increased. On the other hand, higher speed can greatly reduce the measuring time and motion artifacts, which brings comfort to the patients and improves the image quality. In this work, we report a newly developed multifunctional 1050 nm spectral domain optical coherence tomography (SD-OCT) system working at 147 kHz A-scan rate for posterior eye imaging. The uniqueness of this system is: 1) its capability of providing not only simultaneous structural imaging of the complete posterior eye, but also the visualization of the retinal blood vessel network with larger field of view and good image quality compared with former SD-OCT systems; 2) it's fast 147 kHz A-scan rate which has not been reported before. It is demonstrated through in vivo experiments that this system delivers not only superior performance of posterior eye structural imaging but also detailed visualization of microcirculation network in retina. The choroid of the eye with either myopic or normal conditions can clearly be visualized through the entire scanning volume. These results indicate great potential in applying this new system for clinical studies.

Journal of the Optical Society of America A, 2013

As Part V in our series, this paper examines steady-state fluorescence photon diffusion in a homo... more As Part V in our series, this paper examines steady-state fluorescence photon diffusion in a homogenous medium that contains a homogenous distribution of fluorophores, and is enclosed by a "concave" circular cylindrical applicator or is enclosing a "convex" circular cylindrical applicator, both geometries being infinite in the longitudinal dimension. The aim is to predict by analytics and examine with the finite-element method the changing characteristics of the fluorescence-wavelength photon-fluence rate and the ratio (sometimes called the Born ratio) of it versus the excitation-wavelength photon-fluence rate, with respect to the source-detector distance. The analysis is performed for a source and a detector located on the medium-applicator interface and aligned either azimuthally or longitudinally in both concave and convex geometries. When compared to its steady-state counterparts on a semi-infinite medium-applicator interface with the same line-of-sight source-detector distance, the fluorescence-wavelength photon-fluence rate reduces faster along the longitudinal direction and slower along the azimuthal direction in the concave geometry, and conversely in the convex geometry. However, the Born ratio increases slower in both azimuthal and longitudinal directions in the concave geometry and faster in both directions in the convex geometry, respectively, when compared to that in the semi-infinite geometry.

Investigative Opthalmology & Visual Science, 2016

PURPOSE. To investigate the vascular microcirculation changes in the retinal nerve fiber layer (R... more PURPOSE. To investigate the vascular microcirculation changes in the retinal nerve fiber layer (RNFL) in normal, glaucoma suspect, and open-angle glaucoma (OAG) groups using optical coherence tomography-based microangiography (OMAG). METHODS. One eye from each subject was scanned with a Cirrus HD-OCT 5000-based OMAG prototype system montage scanning protocol centered at the optic nerve head (ONH). Blood flow signals were extracted using OMAG algorithm. Retinal nerve fiber layer vascular microcirculation was measured by calculating the blood flux index and vessel area density within a 1.2-mm width annulus centered at the ONH with exclusion of big retinal vessels. One-way ANOVA were performed to analyze the RNFL microcirculation among groups. Linearregression models were constructed to analyze the correlation between RNFL microcirculation and clinical parameters. Discrimination capabilities of the flow metrics were assessed with the area under the receiver operating characteristic curve (AROC). RESULTS. Twenty normal, 26 glaucoma suspect, and 42 OAG subjects were enrolled. Eyes from OAG subjects and glaucoma suspects showed significantly lower blood flux index compared with normal eyes (P 0.0015). Retinal nerve fiber layer blood flow metrics showed significant correlations with visual field indices and structural changes in glaucomatous eyes (P 0.0123). Similar discrimination capability of blood flux index compared with RNFL thickness was found in both disease groups. CONCLUSIONS. Peripapillary RNFL vascular microcirculation measured as blood flux index by OMAG showed significant differences among OAG, glaucoma suspect, and normal controls and was significantly correlated with functional and structural defects. Retinal nerve fiber layer microcirculation measurement using OMAG may help physicians monitor glaucoma.

Scientific reports, Jan 25, 2016

Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal v... more Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal vascular networks without a need for contrast dyes. For sophisticated monitoring and diagnosis of retinal diseases, OCTA capable of providing wide-field and high definition images of retinal vasculature in a single image is desirable. We report OCTA with motion tracking through an auxiliary real-time line scan ophthalmoscope that is clinically feasible to image functional retinal vasculature in patients, with a coverage of more than 60 degrees of retina while still maintaining high definition and resolution. We demonstrate six illustrative cases with unprecedented details of vascular involvement in retinal diseases. In each case, OCTA yields images of the normal and diseased microvasculature at all levels of the retina, with higher resolution than observed with fluorescein angiography. Wide-field OCTA technology will be an important next step in augmenting the utility of OCT technology in...

We demonstrate that, for a long cylindrical applicator that interfaces concavely or convexly with... more We demonstrate that, for a long cylindrical applicator that interfaces concavely or convexly with a scattering-dominant medium, a unique set of spiral-shaped directions exist on the tissue-applicator interface, along which the diffuse photon remission is essentially modeled by the photon remission along a straight line on a semi-infinite interface. This interesting phenomenon, which is validated in steady state in this work by finite-element and Monte Carlo methods, may be particularly useful for simplifying deeper-tissue sensing in endoscopic imaging geometry.