Development of an Online Adaptive Parameter Tuning vSLAM Algorithm for UAVs in GPS-Denied Environments.

In recent years, unmanned aerial vehicles (UAVs) have been applied in many fields owing to their mature flight control technology and easy-to-operate characteristics. No doubt, these UAV-related applications rely heavily on location information provided by the positioning system. Most UAVs nowadays use a global navigation satellite system (GNSS) to obtain location information. However, this outside-in 3rd party positioning system is particularly susceptible to environmental interference and cannot be used in indoor environments, which limits the application diversity of UAVs. To deal with this problem, in this paper, a stereo-based visual simultaneous localization and mapping technology (vSLAM) is applied. The presented vSLAM algorithm fuses onboard inertial measurement unit (IMU) information to further solve the navigation problem in an unknown environment without the use of a GNSS signal and provides reliable localization information. The overall visual positioning system is based on the stereo parallel tracking and mapping architecture (S-PTAM). However, experiments found that the feature-matching threshold has a significant impact on positioning accuracy. Selection of the threshold is based on the Hamming distance without any physical meaning, which makes the threshold quite difficult to set manually. Therefore, this work develops an online adaptive matching threshold according to the keyframe poses. Experiments show that the developed adaptive matching threshold improves positioning accuracy. Since the attitude calculation of the IMU is carried out based on the Mahony complementary filter, the difference between the measured acceleration and the gravity is used as the metric to online tune the gain value dynamically, which can improve the accuracy of attitude estimation under aggressive motions. Moreover, a static state detection algorithm based on the moving window method and measured acceleration is proposed as well to accurately calculate the conversion mechanism between the vSLAM system and the IMU information; this initialization mechanism can help IMU provide a better initial guess for the bundle adjustment algorithm (BA) in the tracking thread. Finally, a performance evaluation of the proposed algorithm is conducted by the popular EuRoC dataset. All the experimental results show that the developed online adaptive parameter tuning algorithm can effectively improve the vSLAM accuracy and robustness.

QUAREP-LiMi: A community-driven initiative to establish guidelines for quality assessment and reproducibility for instruments and images in light microscopy.

A modern day light microscope has evolved from a tool devoted to making primarily empirical observations to what is now a sophisticated , quantitative device that is an integral part of both physical and life science research. Nowadays, microscopes are found in nearly every experimental laboratory. However, despite their prevalent use in capturing and quantifying scientific phenomena, neither a thorough understanding of the principles underlying quantitative imaging techniques nor appropriate knowledge of how to calibrate, operate and maintain microscopes can be taken for granted. This is clearly demonstrated by the well-documented and widespread difficulties that are routinely encountered in evaluating acquired data and reproducing scientific experiments. Indeed, studies have shown that more than 70% of researchers have tried and failed to repeat another scientist's experiments, while more than half have even failed to reproduce their own experiments. One factor behind the reproducibility crisis of experiments published in scientific journals is the frequent underreporting of imaging methods caused by a lack of awareness and/or a lack of knowledge of the applied technique. Whereas quality control procedures for some methods used in biomedical research, such as genomics (e.g. DNA sequencing, RNA-seq) or cytometry, have been introduced (e.g. ENCODE), this issue has not been tackled for optical microscopy instrumentation and images. Although many calibration standards and protocols have been published, there is a lack of awareness and agreement on common standards and guidelines for quality assessment and reproducibility. In April 2020, the QUality Assessment and REProducibility for instruments and images in Light Microscopy (QUAREP-LiMi) initiative was formed. This initiative comprises imaging scientists from academia and industry who share a common interest in achieving a better understanding of the performance and limitations of microscopes and improved quality control (QC) in light microscopy. The ultimate goal of the QUAREP-LiMi initiative is to establish a set of common QC standards, guidelines, metadata models and tools, including detailed protocols, with the ultimate aim of improving reproducible advances in scientific research. This White Paper (1) summarizes the major obstacles identified in the field that motivated the launch of the QUAREP-LiMi initiative; (2) identifies the urgent need to address these obstacles in a grassroots manner, through a community of stakeholders including, researchers, imaging scientists, bioimage analysts, bioimage informatics developers, corporate partners, funding agencies, standards organizations, scientific publishers and observers of such; (3) outlines the current actions of the QUAREP-LiMi initiative and (4) proposes future steps that can be taken to improve the dissemination and acceptance of the proposed guidelines to manage QC. To summarize, the principal goal of the QUAREP-LiMi initiative is to improve the overall quality and reproducibility of light microscope image data by introducing broadly accepted standard practices and accurately captured image data metrics.

Familial retinal arteriolar tortuosity and quantification of vascular tortuosity using swept-source optical coherence tomography angiography.

PURPOSE: Familial retinal arteriolar tortuosity (FRAT) is a rare autosomal dominant disorder that is characterized by tortuosity of the second and higher order retinal arterioles. We implement swept-source optical coherence tomography angiography (SS-OCTA) to quantify vessel tortuosity in patients with FRAT. We hypothesize that patients with FRAT will have higher retinal arteriole tortuosity when compared to controls. METHODS: Patients were scanned with a SS-OCTA device (Plex Elite 9000, Carl Zeiss Meditec, Dublin, CA). Images of a 12 × 12 mm2 area centered on the fovea were processed, and retinal vessels >23.5 µm in diameter were identified. An automatic tortuosity measurement program written in MATLAB was used to assess vessel tortuosity. Branch points in the vessels were detected and used to separate the vasculature into individual segments. The tortuosity was measured by calculating the arc-chord ratio of each vessel segment, where a minimum value of 1 indicated a straight vessel and higher values corresponded to increasing tortuosity. RESULTS: Two patients (4 eyes) with a known history of FRAT and six controls (12 eyes) were enrolled in the study. The mean tortuosity of all vessel segments (MTVS) in scans of FRAT eyes was on average 1.1244 [range: 1.1044-1.1438] while for control eyes it was 1.0818 [range: 1.0746-1.0872]. Average MTVS of FRAT eyes was significantly higher compared to control eyes (p = 0.03). CONCLUSIONS AND IMPORTANCE: Our results are consistent with the hypothesis that patients with FRAT have higher objective measurements of tortuosity compared to controls. Broader applications of this method may be of benefit in other retinal diseases with changes in retinal vessel configuration.

Optic Nerve Head Perfusion Before and After Intravitreal Antivascular Growth Factor Injections Using Optical Coherence Tomography-based Microangiography.

PURPOSE: To use optical coherence tomography angiography (OCTA) to evaluate the changes in optic nerve head perfusion following intravitreal antivascular endothelial growth factor injections. METHODS: Preinjection and postinjection intraocular pressure (IOP) and OCTA images were taken of both the injected and uninjected fellow eyes. RESULTS: Mean preinjection IOP was 16.6±4.7 mm Hg, which increased to a mean of 40.3±13.0 mm Hg (P<0.0001) during the first postinjection image and remained elevated at 36.1±11.5 mm Hg (P<0.0001) during the second postinjection image. Although no significant change was observed in flux, vessel area density, or normalized flux when comparing the OCTA preinjection and first postinjection images, a significant decrease at the second postinjection image was observed (P=0.03, 0.02, and 0.03, respectively). No significant change was observed in the uninjected fellow eye during the same time period (P=0.47, 0.37, and 0.38, respectively). CONCLUSIONS: Following an antivascular endothelial growth factor injection, mean IOP increased significantly and OCTA imaging of the optic nerve demonstrated a mild but significant decrease in optic nerve head perfusion parameters. Clinicians performing these injections should be aware of these findings and monitor the status of the optic nerve in patients undergoing injections.

A Novel Strategy for Quantifying Choriocapillaris Flow Voids Using Swept-Source OCT Angiography.

Purpose: To achieve reproducible imaging of the choriocapillaris and associated flow voids using swept-source OCT angiography (SS-OCTA). Methods: Subjects were enrolled and SS-OCTA was performed using the 3 × 3 mm scan pattern. Blood flow was identified using the complex optical microangiography (OMAG) algorithm. The choriocapillaris was defined as a slab from the outer boundary of Bruch's membrane (BM) to approximately 20 µm below BM. Compensation for the shadowing effect caused by the RPE and BM complex on the choriocapillaris angiogram was achieved by using the structural information from the same slab. A thresholding method to calculate the percentage of flow voids from a region was developed based on a normal database. Results: Twenty normal subjects and 12 subjects with drusen were enrolled. SS-OCTA identified the choriocapillaris in normal subjects as a lobular plexus of capillaries in the central macula and the lobular arrangement became more evident toward the periphery. In all eyes, signal compensation resulted in fewer choriocapillaris flow voids with improved repeatability of measurements. The best repeatability for the measurement was achieved by using 1 standard deviation (SD) for the thresholding strategy. Conclusions: SS-OCTA can image the choriocapillaris in vivo, and the repeatability of flow void measurements is high in the presence of drusen. The ability to image the choriocapillaris and associated flow voids should prove useful in understanding disease onset, progression, and response to therapies.

Natural History of Subclinical Neovascularization in Nonexudative Age-Related Macular Degeneration Using Swept-Source OCT Angiography.

PURPOSE: Swept-source (SS) OCT angiography (OCTA) was used to determine the prevalence, incidence, and natural history of subclinical macular neovascularization (MNV) in eyes with nonexudative age-related macular degeneration (AMD). DESIGN: Prospective, observational, consecutive case series. PARTICIPANTS: Patients with intermediate AMD (iAMD) or geographic atrophy (GA) secondary to nonexudative AMD in 1 eye and exudative AMD in the fellow eye. METHODS: All patients were imaged using both the 3×3 mm and 6×6 mm SS OCTA fields of view (PLEX Elite 9000; Carl Zeiss Meditec, Inc, Dublin, CA). The en face slab used to detect the MNV extended from the outer retina to the choriocapillaris, and projection artifacts were removed using a proprietary algorithm. MAIN OUTCOME MEASURES: Prevalence of subclinical MNV and time to exudation with Kaplan-Meier cumulative estimates of exudation at 1 year. RESULTS: From August 2014 through March 2017, 160 patients underwent SS OCTA (110 eyes with iAMD and 50 eyes with GA). Swept-source OCTA identified subclinical MNV at the time of first imaging in 23 of 160 eyes, for a prevalence of 14.4%. Six eyes demonstrated subclinical MNV during the follow-up. Of 134 eyes with follow-up visits, a total of 13 eyes demonstrated exudation, and of these 13 eyes, 10 eyes were found to have pre-existing subclinical MNV. By 12 months, the Kaplan-Meier cumulative incidence of exudation for all 134 eyes was 6.8%. For eyes with subclinical MNV at the time of first SS OCTA imaging, the incidence was 21.1%, and for eyes without subclinical MNV, the incidence was 3.6%. There was no difference in the cumulative incidence of exudation from pre-existing MNV in eyes with iAMD or GA (P = 0.847, log-rank test). After the detection of subclinical MNV, the risk of exudation was 15.2 times (95% confidence interval, 4.2-55.4) greater compared with eyes without subclinical MNV. CONCLUSIONS: By 12 months, the risk of exudation was greater for eyes with documented subclinical MNV compared with eyes without detectable MNV. For eyes with subclinical MNV, recommendations include more frequent follow-up and home monitoring. Intravitreal therapy is not recommended until prospective studies are performed.

Complex signal-based optical coherence tomography angiography enables in vivo visualization of choriocapillaris in human choroid.

The choriocapillaris (CC) plays an essential role in maintaining the normal functions of the human eye. There is increasing interest in the community to develop an imaging technique for visualizing the CC, yet this remains underexplored due to technical limitations. We propose an approach for the visualization of the CC in humans via a complex signal-based optical microangiography (OMAG) algorithm, based on commercially available spectral domain optical coherence tomography (SD-OCT). We show that the complex signal-based OMAG was superior to both the phase and amplitude signal-based approaches in detailing the vascular lobules previously seen with histological analysis. With this improved ability to visualize the lobular vascular networks, it is possible to identify the feeding arterioles and draining venules around the lobules, which is important in understanding the role of the CC in the pathogenesis of ocular diseases. With built-in FastTrac™ and montage scanning capabilities, we also demonstrate wide-field SD-OCT angiograms of the CC with a field of view at 9×11 mm2.

Comparison of Neovascular Lesion Area Measurements From Different Swept-Source OCT Angiographic Scan Patterns in Age-Related Macular Degeneration.

Purpose: We compared area measurements for the same neovascular lesions imaged using swept source optical coherence tomography angiography (SS-OCTA) and enlarging scan patterns. Methods: Patients with neovascular age-related macular degeneration were imaged using a 100-kHz SS-OCTA instrument (PLEX Elite 9000). The scanning protocols included the 3 × 3, 6 × 6, 9 × 9, and 12 × 12 mm fields of view. Two groups were studied. Group 1 included small lesions contained within the 3 \( \times \) 3 mm scan, and Group 2 included larger lesions that were fully contained within the 6 \( \times \) 6 mm scan. Results: A total of 30 eyes of 26 patients were enrolled in Group 1 and 30 eyes of 25 patients were enrolled in Group 2. In Group 1, the automated mean lesion area measurements were 1.11 (SD = 0.78), 1.14 (SD = 0.80), and 1.27 (SD = 0.82) mm2 for the 3 \( \times \) 3, 6 \( \times \) 6, and 12 \( \times \) 12 mm scans, respectively (ANOVA P < 0.001; post hoc comparisons, P = 0.184, 3 \( \times \) 3 vs. 6 \( \times \) 6 mm; P < 0.001 for the other two pairs). In Group 2, the automated mean lesion area measurements were 5.43 (SD = 2.56), 5.53 (SD = 2.48), and 5.49 (SD = 2.65) mm2 for the 6 \( \times \) 6, 9 \( \times \) 9, and 12 \( \times \) 12 mm scans, respectively (ANOVA P = 0.435; post-hoc comparisons, P = 0.062, 6 \( \times \) 6 vs. 9 \( \times \) 9 mm; P = 0.553, 6 \( \times \) 6 vs. 12 \( \times \) 12 mm; P = 0.654, 9 \( \times \) 9 vs. 12 \( \times \) 12 mm). Conclusions: The similarity in lesion area measurements across different scan patterns suggests that SS-OCTA imaging can be used to follow quantitatively the enlargement of choroidal neovascularization as the disease progresses.

Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications.

OCT has revolutionized the practice of ophthalmology over the past 10-20 years. Advances in OCT technology have allowed for the creation of novel OCT-based methods. OCT-Angiography (OCTA) is one such method that has rapidly gained clinical acceptance since it was approved by the FDA in late 2016. OCTA images are based on the variable backscattering of light from the vascular and neurosensory tissue in the retina. Since the intensity and phase of backscattered light from retinal tissue varies based on the intrinsic movement of the tissue (e.g. red blood cells are moving, but neurosensory tissue is static), OCTA images are essentially motion-contrast images. This motion-contrast imaging provides reliable, high resolution, and non-invasive images of the retinal vasculature in an efficient manner. In many cases, these images are approaching histology level resolution. This unprecedented resolution coupled with the simple, fast and non-invasive imaging platform have allowed a host of basic and clinical research applications. OCTA demonstrates many important clinical findings including areas of macular telangiectasia, impaired perfusion, microaneurysms, capillary remodeling, some types of intraretinal fluid, and neovascularization among many others. More importantly, OCTA provides depth-resolved information that has never before been available. Correspondingly, OCTA has been used to evaluate a spectrum of retinal vascular diseases including diabetic retinopathy (DR), retinal venous occlusion (RVO), uveitis, retinal arterial occlusion, and age-related macular degeneration among others. In this review, we will discuss the methods used to create OCTA images, the practical applications of OCTA in light of invasive dye-imaging studies (e.g. fluorescein angiography) and review clinical studies demonstrating the utility of OCTA for research and clinical practice.

A QRS Detection and R Point Recognition Method for Wearable Single-Lead ECG Devices.

In the new-generation wearable Electrocardiogram (ECG) system, signal processing with low power consumption is required to transmit data when detecting dangerous rhythms and to record signals when detecting abnormal rhythms. The QRS complex is a combination of three of the graphic deflection seen on a typical ECG. This study proposes a real-time QRS detection and R point recognition method with low computational complexity while maintaining a high accuracy. The enhancement of QRS segments and restraining of P and T waves are carried out by the proposed ECG signal transformation, which also leads to the elimination of baseline wandering. In this study, the QRS fiducial point is determined based on the detected crests and troughs of the transformed signal. Subsequently, the R point can be recognized based on four QRS waveform templates and preliminary heart rhythm classification can be also achieved at the same time. The performance of the proposed approach is demonstrated using the benchmark of the MIT-BIH Arrhythmia Database, where the QRS detected sensitivity (Se) and positive prediction (+P) are 99.82% and 99.81%, respectively. The result reveals the approach's advantage of low computational complexity, as well as the feasibility of the real-time application on a mobile phone and an embedded system.

The facial expression of schizophrenic patients applied with infrared thermal facial image sequence.

BACKGROUND: Schizophrenia is a neurological disease characterized by alterations to patients' cognitive functions and emotional expressions. Relevant studies often use magnetic resonance imaging (MRI) of the brain to explore structural differences and responsiveness within brain regions. However, as this technique is expensive and commonly induces claustrophobia, it is frequently refused by patients. Thus, this study used non-contact infrared thermal facial images (ITFIs) to analyze facial temperature changes evoked by different emotions in moderately and markedly ill schizophrenia patients. METHODS: Schizophrenia is an emotion-related disorder, and images eliciting different types of emotions were selected from the international affective picture system (IAPS) and presented to subjects during ITFI collection. ITFIs were aligned using affine registration, and the changes induced by small irregular head movements were corrected. The average temperatures from the forehead, nose, mouth, left cheek, and right cheek were calculated, and continuous temperature changes were used as features. After performing dimensionality reduction and noise removal using the component analysis method, multivariate analysis of variance and the Support Vector Machine (SVM) classification algorithm were used to identify moderately and markedly ill schizophrenia patients. RESULTS: Analysis of five facial areas indicated significant temperature changes in the forehead and nose upon exposure to various emotional stimuli and in the right cheek upon evocation of high valence low arousal (HVLA) stimuli. The most significant P-value (lower than 0.001) was obtained in the forehead area upon evocation of disgust. Finally, when the features of forehead temperature changes in response to low valence high arousal (LVHA) were reduced to 9 using dimensionality reduction and noise removal, the identification rate was as high as 94.3%. CONCLUSIONS: Our results show that features obtained in the forehead, nose, and right cheek significantly differed between moderately and markedly ill schizophrenia patients. We then chose the features that most effectively distinguish between moderately and markedly ill schizophrenia patients using the SVM. These results demonstrate that the ITFI analysis protocol proposed in this study can effectively provide reference information regarding the phase of the disease in patients with schizophrenia.

Signal Normalization Reduces Image Appearance Disparity Among Multiple Optical Coherence Tomography Devices.

PURPOSE: To assess the effect of the previously reported optical coherence tomography (OCT) signal normalization method on reducing the discrepancies in image appearance among spectral-domain OCT (SD-OCT) devices. METHODS: Healthy eyes and eyes with various retinal pathologies were scanned at the macular region using similar volumetric scan patterns with at least two out of three SD-OCT devices at the same visit (Cirrus HD-OCT, Zeiss, Dublin, CA; RTVue, Optovue, Fremont, CA; and Spectralis, Heidelberg Engineering, Heidelberg, Germany). All the images were processed with the signal normalization. A set of images formed a questionnaire with 24 pairs of cross-sectional images from each eye with any combination of the three SD-OCT devices either both pre- or postsignal normalization. Observers were asked to evaluate the similarity of the two displayed images based on the image appearance. The effects on reducing the differences in image appearance before and after processing were analyzed. RESULTS: Twenty-nine researchers familiar with OCT images participated in the survey. Image similarity was significantly improved after signal normalization for all three combinations (P ≤ 0.009) as Cirrus and RTVue combination became the most similar pair, followed by Cirrus and Spectralis, and RTVue and Spectralis. CONCLUSIONS: The signal normalization successfully minimized the disparities in the image appearance among multiple SD-OCT devices, allowing clinical interpretation and comparison of OCT images regardless of the device differences. TRANSLATIONAL RELEVANCE: The signal normalization would enable direct OCT images comparisons without concerning about device differences and broaden OCT usage by enabling long-term follow-ups and data sharing.

Retinal and choroidal vascular features in patients with retinitis pigmentosa imaged by OCT based microangiography.

PURPOSE: To image vascular features of retinitis pigmentosa (RP) using optical coherence tomography angiography (OCTA). METHODS: Patients with RP were imaged by spectral domain optical coherence tomography based angiography (OCTA). The optical microangiography (OMAG) algorithm was applied to scanned datasets to generate 3D OCTA retinal angiograms, i.e., OMAG angiograms. Motion tracking was used to minimize artifacts due to eye movement, and large field of view OMAG angiograms were achieved through a montage scanning protocol. For better visualization, depth volumes were segmented to separate the superficial retinal layers from deep outer retinal layers. The choriocapillaris and other choroidal layers were also segmented. To investigate the changes in retinal architecture, the inner segment/outer segment (IS/OS) junction to RPE layer was segmented to generate en face structural images through averaging intensity projection. Color fundus images and/or Goldmann visual fields were available for comparison of the findings to OMAG images. RESULTS: A total of 25 eyes (13 patients, seven women and six men) diagnosed with RP at various stages were enrolled in this study from October 2014 to January 2016 and imaged by OCTA. The resulting OMAG angiograms provided detailed visualization of retinal and choroidal vascular networks presented within the retina and choroid in a large field of view (FOV) (∼6.7 mm × 6.7 mm). All patients with a severity score greater than 3 showed abnormal microvasculature in both deep retinal and choroidal layers on OMAG images. Images of patients with a score of 4 indicating only peripheral abnormalities demonstrated relatively normal vasculature networks. Microvascular changes in the retinal and choroidal vasculature correlate with structural changes in the slab from IS/OS junction to RPE layer. CONCLUSIONS: OCTA is useful in evaluating the microvascular changes in a large FOV encompassing the maculae of patients with RP. The large FOV of OMAG angiograms, enabled by the motion tracking, provides visualization of high definition and high resolution microvascular networks at varying stages of RP. Microvascular imaging may have significant utility in the diagnosis and monitoring of disease progression in RP patients.

Optical coherence tomography based angiography [Invited].

Optical coherence tomography (OCT)-based angiography (OCTA) provides in vivo, three-dimensional vascular information by the use of flowing red blood cells as intrinsic contrast agents, enabling the visualization of functional vessel networks within microcirculatory tissue beds non-invasively, without a need of dye injection. Because of these attributes, OCTA has been rapidly translated to clinical ophthalmology within a short period of time in the development. Various OCTA algorithms have been developed to detect the functional micro-vasculatures in vivo by utilizing different components of OCT signals, including phase-signal-based OCTA, intensity-signal-based OCTA and complex-signal-based OCTA. All these algorithms have shown, in one way or another, their clinical values in revealing micro-vasculatures in biological tissues in vivo, identifying abnormal vascular networks or vessel impairment zones in retinal and skin pathologies, detecting vessel patterns and angiogenesis in eyes with age-related macular degeneration and in skin and brain with tumors, and monitoring responses to hypoxia in the brain tissue. The purpose of this paper is to provide a technical oriented overview of the OCTA developments and their potential pre-clinical and clinical applications, and to shed some lights on its future perspectives. Because of its clinical translation to ophthalmology, this review intentionally places a slightly more weight on ophthalmic OCT angiography.

Comparison Between Spectral-Domain and Swept-Source Optical Coherence Tomography Angiographic Imaging of Choroidal Neovascularization.

Purpose: The purpose of this study was to compare imaging of choroidal neovascularization (CNV) using swept-source (SS) and spectral-domain (SD) optical coherence tomography angiography (OCTA). Methods: Optical coherence tomography angiography was performed using a 100-kHz SS-OCT instrument and a 68-kHz SD-OCTA instrument (Carl Zeiss Meditec, Inc.). Both 3 × 3- and 6 × 6-mm2 scans were obtained on both instruments. The 3 × 3-mm2 SS-OCTA scans consisted of 300 A-scans per B-scan at 300 B-scan positions, and the SD-OCTA scans consisted of 245 A-scans at 245 B-scan positions. The 6 × 6-mm2 SS-OCTA scans consisted of 420 A-scans per B-scan at 420 B-scan positions, and the SD-OCTA scans consisted of 350 A-scans and 350 B-scan positions. B-scans were repeated four times at each position in the 3 × 3-mm2 scans and twice in the 6 × 6-mm2 scans. Choroidal neovascularization was excluded if not fully contained within the 3 × 3-mm2 scans. The same algorithm was used to detect CNV on both instruments. Two graders outlined the CNV, and the lesion areas were compared between instruments. Results: Twenty-seven consecutive eyes from 23 patients were analyzed. For the 3 × 3-mm2 scans, the mean lesion areas for the SS-OCTA and SD-OCTA instruments were 1.17 and 1.01 mm2, respectively (P = 0.047). For the 6 × 6-mm2 scans, the mean lesion areas for the SS-OCTA and SD-OCTA instruments were 1.24 and 0.74 mm2 (P = 0.003). Conclusions: The areas of CNV tended to be larger when imaged with SS-OCTA than with SD-OCTA, and this difference was greater for the 6 × 6-mm2 scans.

Automated Quantitation of Choroidal Neovascularization: A Comparison Study Between Spectral-Domain and Swept-Source OCT Angiograms.

Purpose: To compare the lesion sizes of choroidal neovascularization (CNV) imaged with spectral-domain (SD) and swept-source (SS) optical coherence tomography angiography (OCTA) and measured using an automated detection algorithm. Methods: Patients diagnosed with CNV were imaged by SD-OCTA and SS-OCTA systems using 3 × 3-mm and 6 × 6-mm scans. The complex optical microangiography (OMAGC) algorithm was used to generate the OCTA images. Optical coherence tomography A datasets for imaging CNV were derived by segmenting from the outer retina to 8 µm below Bruch's membrane. An artifact removal algorithm was used to generate angiograms free of retinal vessel projection artifacts. An automated detection algorithm was developed to quantify the size of the CNV. Automated measurements were compared with manual measurements. Measurements from SD-OCTA and SS-OCTA instruments were compared as well. Results: Twenty-seven eyes from 23 subjects diagnosed with CNV were analyzed. No significant differences were detected between manual and automatic measurements: SD-OCTA 3 × 3-mm (P = 0.61, paired t-test) and 6 × 6-mm (P = 0.09, paired t-test) scans and the SS-OCTA 3 × 3-mm (P = 0.41, paired t-test) and 6 × 6-mm (P = 0.16, paired t-test) scans. Bland-Altman analyses were performed to confirm the agreement between automatic and manual measurements. Mean lesion sizes were significantly larger for the SS-OCTA images compared with the SD-OCTA images: 3 × 3-mm scans (P = 0.011, paired sample t-test) and the 6 × 6-mm scans (P = 0.021, paired t-test). Conclusions: The automated algorithm measurements of CNV were in agreement with the hand-drawn measurements. On average, automated SS-OCTA measurements were larger than SD-OCTA measurements and consistent with the results from using hand-drawn measurements.

Peripapillary Retinal Nerve Fiber Layer Vascular Microcirculation in Eyes With Glaucoma and Single-Hemifield Visual Field Loss.

Importance: Understanding the differences in vascular microcirculation of the peripapillary retinal nerve fiber layer (RNFL) between the hemispheres in eyes with glaucoma with single-hemifield visual field (VF) defects may provide insight into the pathophysiology of glaucoma. Objective: To investigate the changes in the microcirculation of the peripapillary RNFL of eyes with glaucoma by using optical microangiography. Design, Setting, and Participants: Eyes with glaucoma and single-hemifield VF defect and normal eyes underwent scanning using an optical microangiography system covering a 6.7 × 6.7-mm2 area centered at the optic nerve head. The RNFL microcirculation was measured within an annulus region centered at the optic nerve head divided into superior and inferior hemispheres. Blood flux index (the mean flow signal intensity in the vessels) and vessel area density (the percentage of the detected vessels in the annulus) were measured. Main Outcomes and Measures: Differences in microcirculation between the hemispheres in eyes with glaucoma and normal eyes and correlations among blood flow metrics, VF thresholds, and clinical optical coherence tomography structural measurements were assessed. Results: Twenty-one eyes from 21 patients with glaucoma (7 men and 14 women; mean [SD] age, 63.7 [9.9] years) and 20 eyes from 20 healthy control individuals (9 men and 11 women; mean [SD] age, 68.3 [10.7] years) were studied. In eyes with glaucoma, the abnormal hemisphere showed a thinner RNFL (mean [SE] difference, 23.5 [4.5] µm; 95% CI, 15.1-32.0 µm; P < .001), lower RNFL blood flux index (mean [SE] difference, 0.04 [0.01]; 95% CI, 0.02-0.05; P < .001), and less vessel area density (mean [SE] difference, 0.08% [0.02%]; 95% CI, 0.05%-0.10%; P < .001) than did the normal hemisphere. Compared with normal eyes, reduced RNFL microcirculation was found in the normal hemisphere of eyes with glaucoma, measured by mean [SE] differences in blood flux index (0.06 [0.01]; 95% CI, 0.04-0.09; P < .001) and vessel area density (0.04% [0.02%]; 95% CI, 0.02%-0.08%; P = .003) but not in RNFL thickness (3.4 [4.7] µm; 95% CI, -6.2 to 12.9 µm; P = .48). Strong correlations were found between the blood flux index and VF mean deviation (Spearman ρ = 0.44; P = .045) and RNFL thickness (Spearman ρ = 0.65; P = .001) in the normal hemisphere of the eye with glaucoma. Conclusions and Relevance: Reduced RNFL microcirculation was detected in the normal hemisphere of eyes with glaucoma, with strong correspondence with VF loss and RNFL thinning. Although the results suggest that vascular dysfunction precedes structural changes seen in glaucoma, longitudinal studies would be needed to confirm this finding.

Optic Nerve Head Measurements With Optical Coherence Tomography: A Phantom-Based Study Reveals Differences Among Clinical Devices.

PURPOSE: Optical coherence tomography (OCT) can monitor for glaucoma by measuring dimensions of the optic nerve head (ONH) cup and disc. Multiple clinical studies have shown that different OCT devices yield different estimates of retinal dimensions. We developed phantoms mimicking ONH morphology as a new way to compare ONH measurements from different clinical OCT devices. METHODS: Three phantoms were fabricated to model the ONH: One normal and two with glaucomatous anatomies. Phantoms were scanned with Stratus, RTVue, and Cirrus clinical devices, and with a laboratory OCT system as a reference. We analyzed device-reported ONH measurements of cup-to-disc ratio (CDR) and cup volume and compared them with offline measurements done manually and with a custom software algorithm, respectively. RESULTS: The mean absolute difference between clinical devices with device-reported measurements versus offline measurements was 0.082 vs. 0.013 for CDR and 0.044 mm3 vs. 0.019 mm3 for cup volume. Statistically significant differences between devices were present for 16 of 18 comparisons of device-reported measurements from the phantoms. Offline Cirrus measurements tended to be significantly different from those from Stratus and RTVue. CONCLUSIONS: The interdevice differences in CDR and cup volume are primarily caused by the devices' proprietary ONH analysis algorithms. The three devices yield more similar ONH measurements when a consistent offline analysis technique is applied. Scan pattern on the ONH also may be a factor in the measurement differences. This phantom-based study has provided unique insights into characteristics of OCT measurements of the ONH.

Peripapillary Retinal Nerve Fiber Layer Vascular Microcirculation in Glaucoma Using Optical Coherence Tomography-Based Microangiography.

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. Linear-regression 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.

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels.

Optical microangiography (OMAG) is a powerful optical angio-graphic tool to visualize micro-vascular flow in vivo. Despite numerous demonstrations for the past several years of the qualitative relationship between OMAG and flow, no convincing quantitative relationship has been proven. In this paper, we attempt to quantitatively correlate the OMAG signal with flow. Specifically, we develop a simplified analytical model of the complex OMAG, suggesting that the OMAG signal is a product of the number of particles in an imaging voxel and the decorrelation of OCT (optical coherence tomography) signal, determined by flow velocity, inter-frame time interval, and wavelength of the light source. Numerical simulation with the proposed model reveals that if the OCT amplitudes are correlated, the OMAG signal is related to a total number of particles across the imaging voxel cross-section per unit time (flux); otherwise it would be saturated but its strength is proportional to the number of particles in the imaging voxel (concentration). The relationship is validated using microfluidic flow phantoms with various preset flow metrics. This work suggests OMAG is a promising quantitative tool for the assessment of vascular flow.