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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Three-dimensional Advanced Tomographic Procedure for the Imaging of Metallic and Dielectric Targets through GPR Data
摘要： The tomographic algorithms commonly used to process ground penetrating radar (GPR) data assume the scattering phenomenon activated by ideal sources. This can be considered an adequately accurate assumption if the actual GPR antenna presents almost nondirectional features, but should instead properly revisited when a target is illuminated by means of more collimated near-field distributions. In this work, moving from the recent advancements done for two-dimensional scalar GPR imaging theory, we propose a three-dimensional (3-D) vector formulation of the scattering equation, modeling the incident field with the actual field radiated by a directional antenna. Both 3-D dielectric and metallic targets are reconstructed in challenging environments by considering multi- frequency data at microwaves. A comparative analysis is developed through the processing of numerical data by means of a singular-value decomposition as well as an adjoint-operator scheme. The effectiveness of is assessed considering full-wave synthetic data generated on a customized virtual setup based on a commercial tool.
关键词： 3-D imaging,microwave tomography,Ground Penetrating Radar
更新于2025-09-04 15:30:14
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Spectral domain optical coherence tomography as an adjunctive tool for screening Beh?et uveitis
摘要： Background This study investigated the association of central macular thickness (CMT) and macular volume (MV) with severity of Behc?et uveitis in the absence of macular edema (ME). Methods This retrospective, interventional study included a total 131 treatment-na?ve Behc?et patients with varying degree of uveitis in the absence of ME. The mean CMT and MV were obtained by spectral domain optical coherence tomography (SD ODT). The patients were classified according to the anatomical classification of Behc?et uveitis. The main outcome measure was comparison of mean CMT and MV with the types of Behc?et uveitis. Results Sixty patients (45.8%) with no uveitis, 41 patients (31.3%) with anterior uveitis, 18 patients (13.7%) with posterior uveitis, and 12 patients (9.2%) with panuveitis. The mean CMT were 261.6±22.2 μm in no uveitis, 268.1±17.8 μm in anterior uveitis, 306.4±32.9 μm in posterior uveitis, and 300.4±44.0 μm in panuveitis (P < 0.001). The mean MV was 8.7±0.3 mm3 in those without uveitis, 8.8±0.3 mm3 in anterior uveitis, 9.9±1.1 mm3 in those with posterior uveitis, and 9.7±0.4 mm3 in panuveitis (P < 0.001). Types of Behc?et uveitis was the only significant factor correlated with the mean CMT (B = 18.170, β = 0.408, P < 0.001) and the mean MV (B = 0.328, β = 0.652, P < 0.001). Conclusions The mean CMT and MV were significantly thicker in the Behc?et uveitis with posterior involvement. SD OCT can be used for an adjunctive tool for screening Behc?et uveitis, especially for the presence of posterior involvement.
关键词： Behc?et uveitis,macular volume,posterior involvement,spectral domain optical coherence tomography,central macular thickness
更新于2025-09-04 15:30:14
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Evaluation of Ocular Perfusion in Alzheimer’s Disease Using Optical Coherence Tomography Angiography
摘要： Background: There is increasing evidence for the involvement of cerebrovascular factors in Alzheimer’s disease (AD). Objective: To evaluate retinal and optic nerve head perfusion in patients with AD using optical coherence tomography angiography (OCTA), and to analyze the correlations of quantitative OCTA metrics with AD pathology and vascular cerebral lesions in AD patients. Methods: 36 eyes of 36 patients with AD (study group) and 38 eyes of 38 healthy subjects (control group) were prospectively included in this study. OCTA was performed using RTVue XR Avanti with AngioVue. In addition, patients underwent a detailed ophthalmological and neurological examination including Mini-Mental State Examination, cerebral magnetic resonance imaging, and amyloid-β (Aβ) and tau levels in the cerebrospinal fluid (CSF). Results: The flow density in the superficial retinal OCT angiogram of the macula in the study group was significantly lower compared to the control group (p = 0.001). There was a significant correlation between the flow density in the superficial retinal OCT angiogram of the macula, as measured using OCTA, and the Fazekas scale (Spearman’s correlation coefficient = –0.520; p = 0.003). There was no significant correlation between the Aβ or tau levels in the CSF and the flow density data. Conclusion: Patients with AD showed a reduced flow density in the radial peripapillary capillaries layer and in the superficial retinal OCT angiogram when compared with healthy controls. The reduced retinal flow density measured using OCTA is not specifically associated with AD pathology but is associated with the vascular cerebral lesions in AD.
关键词： optical coherence tomography angiography,retinal and optic nerve head perfusion,Alzheimer’s disease,flow density
更新于2025-09-04 15:30:14
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Modeling clustered activity increase in amyloid-beta positron emission tomographic images with statistical descriptors
摘要： Background: Amyloid-beta (Aβ) imaging with positron emission tomography (PET) holds promise for detecting the presence of Aβ plaques in the cortical gray matter. Many image analyses focus on regional average measurements of tracer activity distribution; however, considerable additional information is available in the images. Metrics that describe the statistical properties of images, such as the two-point correlation function (S2), have found wide applications in astronomy and materials science. S2 provides a detailed characterization of spatial patterns in images typically referred to as clustering or flocculence. The objective of this study was to translate the two-point correlation method into Aβ-PET of the human brain using 11C-Pittsburgh compound B (11C-PiB) to characterize longitudinal changes in the tracer distribution that may reflect changes in Aβ plaque accumulation. Methods: We modified the conventional S2 metric, which is primarily used for binary images and formulated a weighted two-point correlation function (wS2) to describe nonbinary, real-valued PET images with a single statistical function. Using serial 11C-PiB scans, we calculated wS2 functions from two-dimensional PET images of different cortical regions as well as three-dimensional data from the whole brain. The area under the wS2 functions was calculated and compared with the mean/median of the standardized uptake value ratio (SUVR). For three-dimensional data, we compared the area under the wS2 curves with the subjects’ cerebrospinal fluid measures. Results: Overall, the longitudinal changes in wS2 correlated with the increase in mean SUVR but showed lower variance. The whole brain results showed a higher inverse correlation between the cerebrospinal Aβ and wS2 than between the cerebrospinal Aβ and SUVR mean/median. We did not observe any confounding of wS2 by region size or injected dose. Conclusion: The wS2 detects subtle changes and provides additional information about the binding characteristics of radiotracers and Aβ accumulation that are difficult to verify with mean SUVR alone.
关键词： positron emission tomography,statistical descriptors,two-point correlation function,amyloid-beta plaques,11C-Pittsburgh compound B
更新于2025-09-04 15:30:14
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OCT-Leakage: A New Method to Identify and Locate Abnormal Fluid Accumulation in Diabetic Retinal Edema
摘要： To identify retinal extracellular fluid changes and their correlation with increased retinal thickness (RT) in eyes with subclinical and clinical macular edema in diabetes type 2. A cohort of 48 eyes from 48 type 2 diabetic patients with mild or moderate nonproliferative diabetic retinopathy (Early Treatment Diabetic Retinopathy Study levels 20/35) were classified as having normal RT (10), subclinical macular edema (30), or clinical macular edema (8). They were examined with Cirrus spectral-domain optical coherence tomography (OCT) at baseline visits (ClinicalTrials.gov number, NCT01145599) in the Coimbra center. Results from automated analysis of the retinal extracellular space, using our OCT-Leakage algorithm to identify sites of low optical reflectivity, were compared with those from a control group of 25 healthy eyes. The highest increases in RT in the eyes with subclinical and clinical macular edema were found in the inner nuclear layer (INL). These increases were, on average, 49.9% in subclinical macular edema and 104.7% in clinical macular edema. Extracellular space increases in the INL that were identified with the OCT-Leakage algorithm showed a strong positive correlation with the increases in RT in the central subfield (r ? 0.71, P < 0.001). Increases in number of sites with lower optical reflectivity positively correlate with the increase in RT in the initial stages of macular edema in diabetes type 2. Diabetic macular edema is represented mainly by extracellular fluid accumulation that preferentially involves the INL of the retina.
关键词： diabetes,optical coherence tomography,macular edema,retinal leakage,blood-retinal barrier
更新于2025-09-04 15:30:14
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Macular Inner Retinal Layer Thickness in Relation to Photopic and Mesopic Contrast Sensitivity in Healthy Young and Older Subjects
摘要： PURPOSE. To examine relationships between the thicknesses of ganglion cell (GC)-related macular layers and central photopic or mesopic contrast sensitivity (CS) in healthy eyes. METHODS. Measurements were made in 38 young and 38 older healthy individuals. Total, inner, layer (IRL) thicknesses were measured in the macula region through and outer retinal spectral-domain optical coherence tomography (SD-OCT) across three sub?elds, or rings, centered at the fovea: central foveal, pericentral, and peripheral. Ganglion cell complex and circumpapillary retinal nerve ?ber layer thicknesses were also measured. Low-spatial-frequency CS for gratings presented at the central 108 visual ?eld were measured through computerized psychophysical tests under photopic and mesopic conditions. Relationships were examined by uni- and multivariate regression analysis. RESULTS. Peripheral IRL thickness emerged as the only independent predictor of photopic CS (P ? 0.001) in the young group and of photopic (P ? 0.026) and mesopic CS (P ? 0.001) in the older group. The slopes of regression lines used to predict CS from peripheral IRL thickness were signi?cantly different for pair-wise comparisons of both photopic CS and age group (P ? 0.0001) and mesopic CS (P ? 0.0001) and age group. These models explained 37% of the variability in photopic CS and 36% of the variability in mesopic CS. CONCLUSIONS. Macular IRL thinning likely due to GC loss was related to reduced photopic and mesopic CS in older healthy eyes. In contrast, in the young eyes, a thicker macular IRL, possibly indicating transient gliosis, was associated with reduced CS.
关键词： contrast sensitivity,optical coherence tomography,retinal ganglion cells,macular inner retinal layer thickness,mesopic vision,glial cells
更新于2025-09-04 15:30:14
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Full-Field Optical Coherence Tomography as a Diagnosis Tool: Recent Progress with Multimodal Imaging
摘要： Full-?eld optical coherence tomography (FF-OCT) is a variant of OCT that is able to register 2D en face views of scattering samples at a given depth. Thanks to its superior resolution, it can quickly reveal information similar to histology without the need to physically section the sample. Sensitivity and speci?city levels of diagnosis performed with FF-OCT are 80% to 95% of the equivalent histological diagnosis performances and could therefore bene?t from improvement. Therefore, multimodal systems have been designed to increase the diagnostic performance of FF-OCT. In this paper, we will discuss which contrasts can be measured with such multimodal systems in the context of ex vivo biological tissue examination. We will particularly emphasize three multimodal combinations to measure the tissue mechanics, dynamics, and molecular content respectively.
关键词： dynamics,multimodality,cellular metabolism,?uorescence microscopy,biomechanics,mechanical properties,full-?eld optical coherence tomography
更新于2025-09-04 15:30:14
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LC-MS Supported Studies on the in Vitro Metabolism of both Enantiomers of Flubatine and the in Vivo Metabolism of (+)-[18F]Flubatine—A Positron Emission Tomography Radioligand for Imaging α4β2 Nicotinic Acetylcholine Receptors
摘要： Both enantiomers of [18F]flubatine are promising radioligands for neuroimaging of α4β2 nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET). To support clinical studies in patients with early Alzheimer’s disease, a detailed examination of the metabolism in vitro and in vivo has been performed. (+)- and (?)-flubatine, respectively, were incubated with liver microsomes from mouse and human in the presence of NADPH (β-nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salt). Phase I in vitro metabolites were detected and their structures elucidated by LC-MS/MS (liquid chromatography-tandem mass spectrometry). Selected metabolite candidates were synthesized and investigated for structural confirmation. Besides a high level of in vitro stability, the microsomal incubations revealed some species differences as well as enantiomer discrimination with regard to the formation of monohydroxylated products, which was identified as the main metabolic pathway in this assay. Furthermore, after injection of 250 MBq (+)-[18F]flubatine (specific activity > 350 GBq/μmol) into mouse, samples were prepared from brain, liver, plasma, and urine after 30 min and investigated by radio-HPLC (high performance liquid chromatography with radioactivity detection). For structure elucidation of the radiometabolites of (+)-[18F]flubatine formed in vivo, identical chromatographic conditions were applied to LC-MS/MS and radio-HPLC to compare samples obtained in vitro and in vivo. By this correlation approach, we assigned three of four main in vivo radiometabolites to products that are exclusively C- or N-hydroxylated at the azabicyclic ring system of the parent molecule.
关键词： epibatidine,liquid chromatography-mass spectrometry (LC-MS),flubatine,NCFHEB,liver microsomes,nicotinic acetylcholine receptors (nAChRs),radiometabolites,positron emission tomography (PET)
更新于2025-09-04 15:30:14
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Current OCT Approaches Do Not Reliably Identify TCFAs
摘要： It is now clearly established that Thin-Capped Fibroatheromas (TCFAs) lead to most Acute Coronary Syndromes (ACSs). The ability to selectively intervene on TCFAs predisposed to rupture and ACSs would dramatically alter the practice of cardiology. While the ability of OCT to identify thin walled plaques at micron scale resolutions has represented a major advance, it is a misconception that it can reliably identify TCFAs. One major reason is that the ‘diffuse border’ criteria currently used to determine ‘lipid plaque’ is almost undoubtedly from high scattering in the intima and not because of core composition (necrotic core). A second reason is that, rather than looking at lipid collections, studies need to be focused on identifying necrotic cores with OCT. Necrotic cores are characteristic of TCFAs and not lipid collections. Numerous other OCT approaches are available which can potentially accurately assess TCFAs, but these have not been aggressively pursed which we believe likely stems in part from the misconceptions over the efficacy of ‘diffuse borders’.
关键词： Myocardial infarction,Optical coherence tomography: OCT,Macrophages,Plaque rupture,Acute coronary syndrome: ACS,Thin capped fibroatheroma: TCFA,Lipid,Massachusetts General Hospital Lightlab
更新于2025-09-04 15:30:14
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Retinal and Optic Disc Alterations in Alzheimer ’s Disease: the Eye as a Potential Central Nervous System Window
摘要： Pathologic changes in the retina and optic nerve are observed in patients with Alzheimer′s disease (AD), even in early stages of the dementia. In our clinical ophthalmology practice, we use optical coherence tomography (OCT), a noninvasive, rapid, objective, and reliable technology that enables for quantification of the retinal nerve fiber layer (RNFL), namely the retinal ganglion cell axons that eventually form the optic nerve. The opportunity to analyze a part of the central nervous system by such a simple exploration led to several studies demonstrating thinning of the RNFL and central retina in AD patients compared with healthy subjects. Here we present some of our investigations in AD patients using Spectral Domain-OCT. Our results suggest that axonal loss secondary to pathologic alterations in the brains of AD patients can be observed by OCT. We also analyzed the association between retinal and RNFL thicknesses and neurologic characteristics, disease duration and severity, and found that mean RNFL thickness was significantly correlated with disease duration, indicating that the progression of AD is associated with a progressive loss of ganglion cells.
关键词： Retinal nerve fiber layer,Retinal thickness,Optic disc,Optical coherence tomography,Alzheimer’s disease
更新于2025-09-04 15:30:14