- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Urban Tomographic Imaging Using Polarimetric SAR Data
摘要： In this paper, we investigate the potential of polarimetric Synthetic Aperture Radar (SAR) tomography (Pol-TomoSAR) in urban applications. TomoSAR exploits the amplitude and phase of the received data and offers the possibility to resolve multiple scatters lying in the same range–azimuth resolution cell. In urban environments, this issue is very important since layover causes multiple coherent scatterers to be mapped in the same range–azimuth image pixel. To achieve reliable and accurate results, TomoSAR requires a large number of multi-baseline acquisitions which, for satellite-borne SAR systems, are collected with long time intervals. Then, accurate tomographic reconstructions would require multiple scatterers to remain stable between all the acquisitions. In this paper, an extension of a generalized likelihood ratio test (GLRT)-based tomographic approach, denoted as Fast-Sup-GLRT, to the polarimetric data case is introduced, with the purpose of investigating if, in urban applications, the use of polarimetric channels allows for reduction of the number of baselines required to achieve a given scatterer’s detection performance. The results presented show that the use of dual polarization data allows the proposed detector to work in an equivalent or better way than use of a double number of independent single polarization channels.
关键词： generalized likelihood ratio test,synthetic aperture radar,sparse signals,polarimetry,radar detection,tomography
更新于2025-09-23 15:22:29
-
Practical Challenges of Current Video Rate OCT Elastography: Accounting for Dynamic and Static Tissue Properties
摘要： Optical coherence tomography (OCT) elastography (OCTE) has the potential to be an important diagnostic tool for pathologies including coronary artery disease, osteoarthritis, malignancies, and even dental caries. Many groups have performed OCTE, including our own, using a wide range of approaches. However, we will demonstrate current OCTE approaches are not scalable to real-time, in vivo imaging. As will be discussed, among the most important reasons is current designs focus on the system and not the target. Specifically, tissue dynamic responses are not accounted, with examples being the tissue strain response time, preload variability, and conditioning variability. Tissue dynamic responses, and to a lesser degree static tissue properties, prevent accurate video rate modulus assessments for current embodiments. Accounting for them is the focus of this paper. A top-down approach will be presented to overcome these challenges to real time in vivo tissue characterization. Discussed first is an example clinical scenario where OCTE would be of substantial relevance, the prevention of acute myocardial infarction or heart attacks. Then the principles behind OCTE are examined. Next, constrains on in vivo application of current OCTE are evaluated, focusing on dynamic tissue responses. An example is the tissue strain response, where it takes about 20 msec after a stress is applied to reach plateau. This response delay is not an issue at slow acquisition rates, as most current OCTE approaches are preformed, but it is for video rate OCTE. Since at video rate each frame is only 30 msec, for essentially all current approaches this means the strain for a given stress is changing constantly during the B-scan. Therefore the modulus can’t be accurately assessed. This serious issue is an even greater problem for pulsed techniques as it means the strain/modulus for a given stress (at a location) is unpredictably changing over a B-scan. The paper concludes by introducing a novel video rate approach to overcome these challenges.
关键词： Optical Coherence Tomography,Elastography,Thin-capped fibroatheromas
更新于2025-09-23 15:22:29
-
Reproducibility of Disc and Macula Optical Coherence Tomography using the Canon OCT-HS100 as Compared with the Zeiss Cirrus HD-OCT
摘要： Purpose: In a clinical setting, the usefulness of optical coherence tomography (OCT) is strongly dependent on reproducibility of the measurement. The aim of the present study was to evaluate macula and optic disc measurement reproducibility with the new spectral-domain OCT (SD-OCT) from Canon (Canon OCT-HS100) and to compare reproducibility and obtained measurements with the Zeiss Cirrus HD-OCT. Methods: Macula and optic disc parameters from the right eyes of 31 subjects were obtained twice with both instruments. Interoperator reproducibility was evaluated by use of the coefficient of repeatability (CR), and the obtained measurements were compared between the instruments. Results: No difference in interoperator reproducibility could be found when comparing the 2 instruments and reproducibility ranged from 3.94% to 12.77% for optic disc parameters and from 1.19% to 3.54% for macula parameters. The lowest reproducibility was found for cup volume and vertical cup/disc ratio with both instruments. For all macula and retinal nerve fiber layer (RNFL) thickness measurements, there was a statistical difference when comparing the 2 instruments, except for RFNL measurements of the superior quadrant, with the Canon OCT-HS100 always evaluating the thickness to be thicker; however, the 2 instruments correlated well. Conclusions: The Canon OCT-HS100 is a reproducible instrument that matches the Zeiss Cirrus HD-OCT well. It remains to be evaluated how sensitive the Canon OCT-HS100 is to detect small subtle changes in optic disc parameters and macular nerve fiber layer thickness. Furthermore, due to the differences in thickness estimation, it is important to emphasize that SD-OCTs are not interchangeable.
关键词： Canon OCT-HS100,Reproducibility,Spectral domain,Optical coherence tomography
更新于2025-09-23 15:22:29
-
Autofluorescence and spectral-domain optical coherence tomography of optic disk melanocytoma
摘要： The authors report fundus autofluorescence (FAF) and spectral-domain optical coherence tomography (OCT ) findings of two consecutive patients who presented with optic disk melanocytoma (ODM). A retrospective study was performed by reviewing medical records and ophthalmic imaging examinations. Optical coherence tomography findings were sloped and brightly reflective anterior tumor surface, adjacent retinal desorganization and abrupt posterior optical shadowing. Vitreous seeds were found in one patient. Fundus autofluorescence revealed outstanding hypoautofluorescence at the tumor area and isoautofluorescence at the remaining retina. Optical coherence tomography findings of the reported cases are consistent with those reported in the reviewed literature. Fundus autofluorescence has been used in the assessment of choroidal melanocytic tumors, but not yet in melanocytomas. We assume that this is the first report of these findings and believe that when its pattern has become clearly defined, fundus autofluorescence will be a useful tool to avoid misdiagnosis in suspicious cases and for follow-up.
关键词： Melanoma/diagnosis,Female,Adult,Male,Case reports,Optic nerve neoplasms/diagnosis,Fluorescein angiography,Humans,Tomography, optical coherence
更新于2025-09-23 15:22:29
-
Evaluation of choroidal and retinal thickness measurements in adult hemodialysis patients using spectral-domain optical coherence tomography
摘要： Purpose: To assess the effect of hemodialysis on retinal and choroidal thicknesses using spectral-domain optical coherence tomography (SD-OCT). Methods: In this prospective interventional study, 25 hemodialysis patients (17 male, 8 female) were enrolled. All participants underwent high-speed, high-resolution SD-OCT (λ=840 mm; 26.000 A-scans/s; 5 μm resolution) before and after hemodialysis. Choroidal thickness was measured perpendicularly from the outer edge of the retinal pigment epithelium to the choroid-sclera boundary at the fovea and at five additional points: 500 μm and 1000 μm nasal to the fovea and 500 μm, 1000 μm, and 1500 μm temporal to the fovea. Two masked physicians performed the measurements. Choroidal and retinal thicknesses before and after hemodialysis were compared. results: The median choroidal thicknesses before and after hemodialysis were 182 μm (range, 103-374 μm) and 161 μm (range, 90-353 μm), respectively (P<0.001). The median retinal thicknesses were 246 μm (range, 179-296 μm) before and 248 μm (range, 141-299 μm) after hemodialysis (P>0.05). Systolic arterial pressure, diastolic arterial pressure, mean arterial pressure, heart rate, and ocular perfusion pressure significantly decreased after hemodialysis (P<0.001). Intraocular pressure did not vary significantly (P=0.540). conclusion: Hemodialysis seems to cause a significant decrease in choroidal thickness, whereas it has no effect on retinal thickness. This significant decrease in choroidal thickness might be due to the extensive fluid absorption in hemodialysis, which could result in decreased ocular blood flow.
关键词： Choroidal thickness,Hemodialysis,Optical coherence tomography
更新于2025-09-23 15:22:29
-
Semi-supervised Automatic Segmentation of Layer and fluid region in Retinal Optical Coherence Tomography Images Using Adversarial Learning
摘要： Optical coherence tomography (OCT) is a primary imaging technique for ophthalmic diagnosis due to its advantages in high resolution and non-invasiveness. Diabetes is a chronic disease, which could cause retinal layer deformation and fluid accumulation. It might increase the risk of blindness, and thus, it is important to monitor the morphology change of the retinal layer and fluid accumulation for diabetes patients. Due to the existence of deformation and fluid accumulation, the retinal layer and fluid region segmentation in the OCT image is a challenging task. Machine learning-based segmentation methods have been proposed, but they depend on a significant number of pixel-level annotated data, which is often unavailable. In this paper, we proposed a new semi-supervised fully convolutional deep learning method for segmenting retinal layers and fluid regions in retinal OCT B-scans. The proposed semi-supervised method leverages the unlabeled data through an adversarial learning strategy. The segmentation method includes a segmentation network and a discriminator network, and both the networks are with U-Net alike fully convolutional architecture. The objective function of the segmentation network is a joint loss function, including multi-class cross entropy loss, dice overlap loss, adversarial loss, and semi-supervised loss. We show that the discriminator network and the use of unlabeled data can improve the performance of segmentation. The proposed method is investigated on the duke Diabetic Macular Edema dataset and the POne dataset, and the experiment results demonstrate that our method is more effective than the other state-of-the-art methods for layers and fluid segmentation in the OCT images.
关键词： image processing,optical coherence tomography,layer segmentation,Adversarial learning,convolutional neural networks
更新于2025-09-23 15:22:29
-
[IEEE 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Krakow (2018.10.16-2018.10.18)] 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - A Fast Way to Get Sensitivity Map of Wire-Mesh
摘要： This paper presents a new method for obtaining the sensitivity map of a wire-mesh sensor (WMS) based on the Maxwell-Wagner effect. The sensitivity map is crucial for the accuracy of electrical capacitance tomography (ECT) in industrial process monitoring. Traditional methods for sensitivity map calculation are complex and time-consuming. The proposed method simplifies this by using a simulation approach that models the WMS as a two-phase flow sensor. The results show that the new sensitivity map improves the imaging quality and reduces the computational time compared to conventional methods. This method is validated through simulations and experiments, demonstrating its effectiveness for practical applications in multiphase flow measurement.
关键词： wire-mesh tomography,sensitivity map,simulation
更新于2025-09-23 15:22:29
-
[IEEE 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Krakow, Poland (2018.10.16-2018.10.18)] 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Compensation for fringe effect of electrical resistance tomography sensor by multiple-plane sensor scheme
摘要： Fringe effect exists in conventional ERT sensors, i.e. severe distortions of electric field on both ends of sensor electrodes. This leads to a 3D sensing region for a 2D ERT sensor. As a result, the objects outside the ERT sensor plane can still be sensed and imaged, which is undesired and deteriorates the image accuracy. To tackle with this issue, a three-plane ERT sensor scheme is proposed. Simulation results show that the three-plane sensor scheme can compensate for the fringe effect induced by the object outside the measurement sensor plane regarding a distribution with three non-conductive bars at different cross-sectional and axial positions. Meanwhile, it is found that for axially uniform distributions, the proposed compensation method can reduce the size overestimation of non-conductive objects to be imaged by linear reconstruction method such as the Landweber iteration. Finally, an experimental ERT system is established to verify the findings from simulation.
关键词： Electrical resistance tomography,Fringe effect
更新于2025-09-23 15:22:29
-
Polarization-Sensitive Optical Coherence Tomography for Brain Tumor Characterization
摘要： Complete removal of brain tumor is of the most interest to a surgeon because the resection area directly relates to recurrence rate. Although there are many biomedical imaging modalities applied to locate the positions of tumors, they lack the spatial resolution to precisely delineate the boundary between brain tumor and normal brain tissues and are also inconvenient to be used intraoperatively. This study aims to examine the feasibility of label-free, polarization-sensitive optical coherence tomography (PS-OCT) for distinguishing brain tumors from normal brain tissues. Ex vivo samples were obtained from two patients with grade II and II-III glioma; healthy porcine brain tissues were utilized as the control group. In the results obtained from normal porcine brain, white matter contains significantly higher birefringent property over grey matter indicated by phase retardation. Based on the knowledge obtained from porcine brain experiment, a similar high-birefringent tissue is observed partially on the edge of the sliced glioma, and such tissue is considered as white matter because glioma originates through the mutation of the healthy white matter's glia cells. Additionally, differences between grey matter and brain tumor are not apparent based on phase retardation images and further histogram analysis. The capability of PS-OCT for distinguishing glioma from white matter is demonstrated. It could be a potential system to facilitate safe and maximum resection area, and finally, lead to ameliorated outcomes.
关键词： optical polarization,white matter,Brain tumor,optical coherence tomography
更新于2025-09-23 15:22:29
-
Choroidal imaging biomarkers
摘要： The choroid is the vascular coat of the eye,and its role has been studied in multiple chorioretinal disorders. The recent advancements in choroidal imaging techniques including enhanced depth imaging optical coherence tomography (EDI-OCT), swept source (SS-OCT), enface OCT and OCT angiography have facilitated an in-depth analysis of choroid. The gradual shift from manual to automated segmentation and binarization methods have led to precise and reproducible measurements of choroidal parameters. These qualitative and quantitative parameters, called choroidal imaging biomarkers, have evolved over the past decade from a simple linear subfoveal choroidal thickness to more complex 3 dimensional (3-D) choroidal reconstruction thus widening the spectrum encompassing multiple parameters. These biomarkers have provided a better understanding of the pathogenesis, are helpful in diagnostic dilemmas, and in future may also help to devise treatment options. The lack of normative data, absence of standardized parameters and limitations of the imaging techniques, however, have led to ambiguity and difficulty in the interpretation of these variables. We attempt to address these lacunae in the literature and provide a basic understanding of the choroid in both health and disease using these choroidal biomarkers.
关键词： Optical coherence tomography angiography (OCTA),En-face OCT,Swept source optical coherence tomography (SS-OCT),Choroidal thickness,Choroidal vascularity index (CVI),Choroidal imaging biomarkers,Choroidal volume
更新于2025-09-23 15:21:21