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Lorenzo Bruzzone - One of the best experts on this subject based on the ideXlab platform.
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unsupervised deep change Vector Analysis for multiple change detection in vhr images
IEEE Transactions on Geoscience and Remote Sensing, 2019Co-Authors: Sudipan Saha, Francesca Bovolo, Lorenzo BruzzoneAbstract:Change detection (CD) in multitemporal images is an important application of remote sensing. Recent technological evolution provided very high spatial resolution (VHR) multitemporal optical satellite images showing high spatial correlation among pixels and requiring an effective modeling of spatial context to accurately capture change information. Here, we propose a novel unsupervised context-sensitive framework—deep change Vector Analysis (DCVA)—for CD in multitemporal VHR images that exploit convolutional neural network (CNN) features. To have an unsupervised system, DCVA starts from a suboptimal pretrained multilayered CNN for obtaining deep features that can model spatial relationship among neighboring pixels and thus complex objects. An automatic feature selection strategy is employed layerwise to select features emphasizing both high and low prior probability change information. Selected features from multiple layers are combined into a deep feature hyperVector providing a multiscale scene representation. The use of the same pretrained CNN for semantic segmentation of single images enables us to obtain coherent multitemporal deep feature hyperVectors that can be compared pixelwise to obtain deep change Vectors that also model spatial context information. Deep change Vectors are analyzed based on their magnitude to identify changed pixels. Then, deep change Vectors corresponding to identified changed pixels are binarized to obtain a compressed binary deep change Vectors that preserve information about the direction (kind) of change. Changed pixels are analyzed for multiple CD based on the binary features, thus implicitly using the spatial information. Experimental results on multitemporal data sets of Worldview-2, Pleiades, and Quickbird images confirm the effectiveness of the proposed method.
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multiscale morphological compressed change Vector Analysis for unsupervised multiple change detection
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2017Co-Authors: Sicong Liu, Xiaohua Tong, Alim Samat, Lorenzo Bruzzone, Francesca BovoloAbstract:A novel multiscale morphological compressed change Vector Analysis (M2C2VA) method is proposed to address the multiple-change detection problem (i.e., identifying different classes of changes) in bitemporal remote sensing images. The proposed approach contributes to extend the state-of-the-art spectrum-based compressed change Vector Analysis (C2VA) method by jointly analyzing the spectral-spatial change information. In greater details, reconstructed spectral change Vector features are built according to a morphological Analysis. Thus more geometrical details of change classes are preserved while exploiting the interaction of a pixel with its adjacent regions. Two multiscale ensemble strategies, i.e., data level and decision level fusion, are designed to integrate the change information represented at different scales of features or to combine the change detection results obtained by the detector at different scales, respectively. A detailed scale sensitivity Analysis is carried out to investigate its impacts on the performance of the proposed method. The proposed method is designed in an unsupervised fashion without requiring any ground reference data. The proposed M2C2VA is tested on one simulated and three real bitemporal remote sensing images showing its properties in terms of different image size and spatial resolution. Experimental results confirm its effectiveness.
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sequential spectral change Vector Analysis for iteratively discovering and detecting multiple changes in hyperspectral images
IEEE Transactions on Geoscience and Remote Sensing, 2015Co-Authors: Sicong Liu, Lorenzo Bruzzone, Francesca Bovolo, Massimo ZanettiAbstract:This paper presents an effective semiautomatic method for discovering and detecting multiple changes (i.e., different kinds of changes) in multitemporal hyperspectral (HS) images. Differently from the state-of-the-art techniques, the proposed method is designed to be sensitive to the small spectral variations that can be identified in HS images but usually are not detectable in multispectral images. The method is based on the proposed sequential spectral change Vector Analysis, which exploits an iterative hierarchical scheme that at each iteration discovers and identifies a subset of changes. The approach is interactive and semiautomatic and allows one to study in detail the structure of changes hidden in the variations of the spectral signatures according to a top-down procedure. A novel 2-D adaptive spectral change Vector representation (ASCVR) is proposed to visualize the changes. At each level this representation is optimized by an automatic definition of a reference Vector that emphasizes the discrimination of changes. Finally, an interactive manual change identification is applied for extracting changes in the ASCVR domain. The proposed approach has been tested on three hyperspectral data sets, including both simulated and real multitemporal images showing multiple-change detection problems. Experimental results confirmed the effectiveness of the proposed method.
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a novel sequential spectral change Vector Analysis for representing and detecting multiple changes in hyperspectral images
International Geoscience and Remote Sensing Symposium, 2014Co-Authors: Sicong Liu, Lorenzo Bruzzone, Francesca BovoloAbstract:This paper focuses on a challenging task for representing and detecting multiple changes in multitemporal hyperspectral images. To this aim, a novel Sequential Spectral Change Vector Analysis (S 2 CVA) method is proposed that extends the use of the popular C 2 VA method [1]. The proposed S 2 CVA approach is designed in a sequential and semiautomatic fashion, where a fully automatic 2-D change representation and an interactive change identification are included at each level of the processing, exploiting the multiple change information hierarchically. In particular, an adaptive reference Vector scheme is developed to drive the change representation, and thus the sequential Analysis, by following a top-down structure. Changes are represented and separated according to their spectral change significance. Experimental results obtained on multitemporal Hyperion images confirm the effectiveness of the proposed method.
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a theoretical framework for unsupervised change detection based on change Vector Analysis in the polar domain
IEEE Transactions on Geoscience and Remote Sensing, 2007Co-Authors: Francesca Bovolo, Lorenzo BruzzoneAbstract:This paper addresses unsupervised change detection by proposing a proper framework for a formal definition and a theoretical study of the change Vector Analysis (CVA) technique. This framework, which is based on the representation of the CVA in polar coordinates, aims at: 1) introducing a set of formal definitions in the polar domain (which are linked to the properties of the data) for a better general description (and thus understanding) of the information present in spectral change Vectors; 2) analyzing from a theoretical point of view the distributions of changed and unchanged pixels in the polar domain (also according to possible simplifying assumptions); 3) driving the implementation of proper preprocessing procedures to be applied to multitemporal images on the basis of the results of the theoretical study on the distributions; and 4) defining a solid background for the development of advanced and accurate automatic change-detection algorithms in the polar domain. The findings derived from the theoretical Analysis on the statistical models of classes have been validated on real multispectral and multitemporal remote sensing images according to both qualitative and quantitative analyses. The results obtained confirm the interest of the proposed framework and the validity of the related theoretical Analysis
Francesca Bovolo - One of the best experts on this subject based on the ideXlab platform.
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unsupervised deep change Vector Analysis for multiple change detection in vhr images
IEEE Transactions on Geoscience and Remote Sensing, 2019Co-Authors: Sudipan Saha, Francesca Bovolo, Lorenzo BruzzoneAbstract:Change detection (CD) in multitemporal images is an important application of remote sensing. Recent technological evolution provided very high spatial resolution (VHR) multitemporal optical satellite images showing high spatial correlation among pixels and requiring an effective modeling of spatial context to accurately capture change information. Here, we propose a novel unsupervised context-sensitive framework—deep change Vector Analysis (DCVA)—for CD in multitemporal VHR images that exploit convolutional neural network (CNN) features. To have an unsupervised system, DCVA starts from a suboptimal pretrained multilayered CNN for obtaining deep features that can model spatial relationship among neighboring pixels and thus complex objects. An automatic feature selection strategy is employed layerwise to select features emphasizing both high and low prior probability change information. Selected features from multiple layers are combined into a deep feature hyperVector providing a multiscale scene representation. The use of the same pretrained CNN for semantic segmentation of single images enables us to obtain coherent multitemporal deep feature hyperVectors that can be compared pixelwise to obtain deep change Vectors that also model spatial context information. Deep change Vectors are analyzed based on their magnitude to identify changed pixels. Then, deep change Vectors corresponding to identified changed pixels are binarized to obtain a compressed binary deep change Vectors that preserve information about the direction (kind) of change. Changed pixels are analyzed for multiple CD based on the binary features, thus implicitly using the spatial information. Experimental results on multitemporal data sets of Worldview-2, Pleiades, and Quickbird images confirm the effectiveness of the proposed method.
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multiscale morphological compressed change Vector Analysis for unsupervised multiple change detection
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2017Co-Authors: Sicong Liu, Xiaohua Tong, Alim Samat, Lorenzo Bruzzone, Francesca BovoloAbstract:A novel multiscale morphological compressed change Vector Analysis (M2C2VA) method is proposed to address the multiple-change detection problem (i.e., identifying different classes of changes) in bitemporal remote sensing images. The proposed approach contributes to extend the state-of-the-art spectrum-based compressed change Vector Analysis (C2VA) method by jointly analyzing the spectral-spatial change information. In greater details, reconstructed spectral change Vector features are built according to a morphological Analysis. Thus more geometrical details of change classes are preserved while exploiting the interaction of a pixel with its adjacent regions. Two multiscale ensemble strategies, i.e., data level and decision level fusion, are designed to integrate the change information represented at different scales of features or to combine the change detection results obtained by the detector at different scales, respectively. A detailed scale sensitivity Analysis is carried out to investigate its impacts on the performance of the proposed method. The proposed method is designed in an unsupervised fashion without requiring any ground reference data. The proposed M2C2VA is tested on one simulated and three real bitemporal remote sensing images showing its properties in terms of different image size and spatial resolution. Experimental results confirm its effectiveness.
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sequential spectral change Vector Analysis for iteratively discovering and detecting multiple changes in hyperspectral images
IEEE Transactions on Geoscience and Remote Sensing, 2015Co-Authors: Sicong Liu, Lorenzo Bruzzone, Francesca Bovolo, Massimo ZanettiAbstract:This paper presents an effective semiautomatic method for discovering and detecting multiple changes (i.e., different kinds of changes) in multitemporal hyperspectral (HS) images. Differently from the state-of-the-art techniques, the proposed method is designed to be sensitive to the small spectral variations that can be identified in HS images but usually are not detectable in multispectral images. The method is based on the proposed sequential spectral change Vector Analysis, which exploits an iterative hierarchical scheme that at each iteration discovers and identifies a subset of changes. The approach is interactive and semiautomatic and allows one to study in detail the structure of changes hidden in the variations of the spectral signatures according to a top-down procedure. A novel 2-D adaptive spectral change Vector representation (ASCVR) is proposed to visualize the changes. At each level this representation is optimized by an automatic definition of a reference Vector that emphasizes the discrimination of changes. Finally, an interactive manual change identification is applied for extracting changes in the ASCVR domain. The proposed approach has been tested on three hyperspectral data sets, including both simulated and real multitemporal images showing multiple-change detection problems. Experimental results confirmed the effectiveness of the proposed method.
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a novel sequential spectral change Vector Analysis for representing and detecting multiple changes in hyperspectral images
International Geoscience and Remote Sensing Symposium, 2014Co-Authors: Sicong Liu, Lorenzo Bruzzone, Francesca BovoloAbstract:This paper focuses on a challenging task for representing and detecting multiple changes in multitemporal hyperspectral images. To this aim, a novel Sequential Spectral Change Vector Analysis (S 2 CVA) method is proposed that extends the use of the popular C 2 VA method [1]. The proposed S 2 CVA approach is designed in a sequential and semiautomatic fashion, where a fully automatic 2-D change representation and an interactive change identification are included at each level of the processing, exploiting the multiple change information hierarchically. In particular, an adaptive reference Vector scheme is developed to drive the change representation, and thus the sequential Analysis, by following a top-down structure. Changes are represented and separated according to their spectral change significance. Experimental results obtained on multitemporal Hyperion images confirm the effectiveness of the proposed method.
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a theoretical framework for unsupervised change detection based on change Vector Analysis in the polar domain
IEEE Transactions on Geoscience and Remote Sensing, 2007Co-Authors: Francesca Bovolo, Lorenzo BruzzoneAbstract:This paper addresses unsupervised change detection by proposing a proper framework for a formal definition and a theoretical study of the change Vector Analysis (CVA) technique. This framework, which is based on the representation of the CVA in polar coordinates, aims at: 1) introducing a set of formal definitions in the polar domain (which are linked to the properties of the data) for a better general description (and thus understanding) of the information present in spectral change Vectors; 2) analyzing from a theoretical point of view the distributions of changed and unchanged pixels in the polar domain (also according to possible simplifying assumptions); 3) driving the implementation of proper preprocessing procedures to be applied to multitemporal images on the basis of the results of the theoretical study on the distributions; and 4) defining a solid background for the development of advanced and accurate automatic change-detection algorithms in the polar domain. The findings derived from the theoretical Analysis on the statistical models of classes have been validated on real multispectral and multitemporal remote sensing images according to both qualitative and quantitative analyses. The results obtained confirm the interest of the proposed framework and the validity of the related theoretical Analysis
Vishal Jhanji - One of the best experts on this subject based on the ideXlab platform.
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Vector Analysis of high 3 diopters astigmatism correction using small incision lenticule extraction and laser in situ keratomileusis
Journal of Cataract and Refractive Surgery, 2018Co-Authors: Tommy C. Y. Chan, Alex L K Ng, Vishal Jhanji, Yan Wang, Jiamei Zhang, Marco Yu, George P M ChengAbstract:Purpose To compare the astigmatic correction in high myopic astigmatism between small-incision lenticule extraction and laser in situ keratomileusis (LASIK) using Vector Analysis. Setting Hong Kong Laser Eye Center, Hong Kong. Design Retrospective case series. Methods Patients who had correction of myopic astigmatism of 3.0 diopters (D) or more and had either small-incision lenticule extraction or femtosecond laser–assisted LASIK were included. Only the left eye was included for Analysis. Visual and refractive results were presented and compared between groups. Results The study comprised 105 patients (40 eyes in the small-incision lenticule extraction group and 65 eyes in the femtosecond laser–assisted LASIK group.) The mean preoperative manifest cylinder was −3.42 D ± 0.55 (SD) in the small-incision lenticule extraction group and −3.47 ± 0.49 D in the LASIK group (P = .655). At 3 months, there was no significant between-group difference in uncorrected distance visual acuity (P = .915) and manifest spherical equivalent (P = .145). Ninety percent and 95.4% of eyes were within ± 0.5 D of the attempted cylindrical correction for the small-incision lenticule extraction and LASIK group, respectively (P = .423). Vector Analysis showed comparable target-induced astigmatism (P = .709), surgically induced astigmatism Vector (P = .449), difference Vector (P = .335), and magnitude of error (P = .413) between groups. The absolute angle of error was 1.88 ± 2.25 degrees in the small-incision lenticule extraction group and 1.37 ± 1.58 degrees in the LASIK group (P = .217). Conclusion Small-incision lenticule extraction offered astigmatic correction comparable to LASIK in eyes with high myopic astigmatism.
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Vector Analysis of astigmatic correction after small incision lenticule extraction and femtosecond assisted lasik for low to moderate myopic astigmatism
British Journal of Ophthalmology, 2016Co-Authors: George P M Cheng, Alex L K Ng, Tommy C. Y. Chan, Vishal Jhanji, Cong Ye, Clement C Y Tham, Zheng WangAbstract:Aim To compare astigmatic correction between femtosecond-assisted laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). Methods A total of 111 patients were included in this prospective study. Fifty-seven eyes were treated with LASIK and 54 eyes were treated with SMILE for myopia with low to moderate (−0.25 to −4.0 D) astigmatism. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity and manifest refraction were measured preoperatively and at 1 and 3 months postoperatively. Visual and refractive outcomes were reported. Changes in refractive astigmatism were evaluated using Vector Analysis. Results Preoperative characteristics were similar between both groups. The UDVA at 1 and 3 months was better in the LASIK group compared with the SMILE group (p 0.596) between the two groups. Surgically induced astigmatism was significantly lower in the SMILE group (p 0.122). Conclusions Our results showed that SMILE offered a less favourable astigmatic correction comparable to femtosecond-assisted LASIK in eyes with low to moderate myopic astigmatism. The alignment of treatment was more variable in SMILE, leading to a lower efficacy compared with LASIK by 3 months postoperatively.
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Vector Analysis of corneal astigmatism after combined femtosecond assisted phacoemulsification and arcuate keratotomy
American Journal of Ophthalmology, 2015Co-Authors: George P M Cheng, Tommy C. Y. Chan, Vishal Jhanji, Clement C Y Tham, Zheng Wang, Victor C P WooAbstract:Purpose To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. Design Retrospective, interventional case series. Methods This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector Analysis of the astigmatic changes was performed using the Alpins method. Results Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively ( P Conclusions Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies.
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Vector Analysis of corneal astigmatism after combined femtosecond assisted phacoemulsification and arcuate keratotomy
American Journal of Ophthalmology, 2015Co-Authors: George P M Cheng, Tommy C. Y. Chan, Vishal Jhanji, Clement C Y Tham, Zheng WangAbstract:PURPOSE: To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. DESIGN: Retrospective, interventional case series. METHODS: This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector Analysis of the astigmatic changes was performed using the Alpins method. RESULTS: Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively (P < .001). The magnitude of error (difference between surgically induced and target-induced astigmatism) (-0.13 ± 0.68 D), as well as the correction index (ratio of surgically induced and target-induced astigmatism) (0.86 ± 0.52), demonstrated slight undercorrection. The angle of error was very close to 0, indicating no significant systematic error of misaligned treatment. However, the absolute angle of error showed a less favorable range (17.5 ± 19.2 degrees), suggesting variable factors such as healing or alignment at an individual level. There were no intraoperative or postoperative complications. CONCLUSIONS: Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies.
Elisabetta Marini - One of the best experts on this subject based on the ideXlab platform.
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identifying athlete body fluid changes during a competitive season with bioelectrical impedance Vector Analysis
International Journal of Sports Physiology and Performance, 2020Co-Authors: Francesco Campa, Elisabetta Marini, Steven B Heymsfield, Catarina N Matias, Stefania Toselli, Luis B Sardinha, Analiza M SilvaAbstract:PURPOSE: To analyze the association between body fluid changes evaluated by bioelectrical impedance Vector Analysis and dilution techniques over a competitive season in athletes. METHODS: A total of 58 athletes of both sexes (men: age 18.7 [4.0] y and women: age 19.2 [6.0] y) engaging in different sports were evaluated at the beginning (pre) and 6 months after (post) the competitive season. Deuterium dilution and bromide dilution were used as the criterion methods to assess total body water (TBW) and extracellular water (ECW), respectively; intracellular water (ICW) was calculated as TBW-ECW. Bioelectrical resistance and reactance were obtained with a phase-sensitive 50-kHz bioelectrical impedance Analysis device; bioelectrical impedance Vector Analysis was applied. Dual-energy X-ray absorptiometry was used to assess fat mass and fat-free mass. The athletes were empirically classified considering TBW change (pre-post, increase or decrease) according to sex. RESULTS: Significant mean Vector displacements in the postgroups were observed in both sexes. Specifically, reductions in Vector length (Z/H) were associated with increases in TBW and ICW (r = -.718, P < .01; r = -.630, P < .01, respectively) and decreases in ECW:ICW ratio (r = .344, P < .05), even after adjusting for age, height, and sex. Phase-angle variations were positively associated with TBW and ICW (r = .458, P < .01; r = .564, P < .01, respectively) and negatively associated with ECW:ICW (r = -.436, P < .01). Phase angle significantly increased in all the postgroups except in women in whom TBW decreased. CONCLUSIONS: The results suggest that bioelectrical impedance Vector Analysis is a suitable method to obtain a qualitative indication of body fluid changes during a competitive season in athletes.
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phase angle and bioelectrical impedance Vector Analysis in the evaluation of body composition in athletes
Clinical Nutrition, 2020Co-Authors: Elisabetta Marini, Roberto Buffa, Francesco Campa, Catarina N Matias, Stefania Toselli, Luis B Sardinha, Silvia Stagi, Analiza M SilvaAbstract:Summary Aims To analyze the association of classic and specific bioelectrical impedance Vector Analysis (BIVA) and phase angle with reference techniques for the assessment of body composition in athletes. Methods 202 athletes of both sexes (men: 21.5 ± 5.0; women: 20.7 ± 5.1) engaged in different sports were evaluated during the in-season period. Bioelectrical resistance (R, ohm) and reactance (Xc, ohm) were obtained with a phase-sensitive 50 kHz bioelectrical impedance Analysis device. The classic and specific BIVA procedures, which respectively correct bioelectrical values for body height (R/H and Xc/H, ohm/m) and body geometry (Rsp and Xcsp, ohm cm), were applied. Dual energy X-ray absorptiometry was used as the reference method to assess fat-mass (FM), fat-free mass (FFM) and %FM. Deuterium dilution and bromide dilution where used as the criterion method for total body water (TBW) and extracellular water (ECW), respectively. Intracellular water (ICW) was calculated as TBW minus ECW. Results Specific bioelectrical values (Rsp, Xcsp, Zsp) were positively correlated with FM and %FM (%FM; Zsp men: r = 0.569, p Conclusions Specific BIVA turns out to be more accurate for the Analysis of %FM in athletes, while it does not correctly evaluate TBW, for which classic BIVA appears to be a suitable approach. Phase angles, and hence both BIVA approaches, can detect ECW/ICW changes.
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phase angle and bioelectrical impedance Vector Analysis in the evaluation of body composition in athletes
Clinical Nutrition, 2020Co-Authors: Elisabetta Marini, Roberto Buffa, Francesco Campa, Catarina N Matias, Stefania Toselli, Luis B Sardinha, Silvia Stagi, Analiza M SilvaAbstract:Summary Aims To analyze the association of classic and specific bioelectrical impedance Vector Analysis (BIVA) and phase angle with reference techniques for the assessment of body composition in athletes. Methods 202 athletes of both sexes (men: 21.5 ± 5.0; women: 20.7 ± 5.1) engaged in different sports were evaluated during the in-season period. Bioelectrical resistance (R, ohm) and reactance (Xc, ohm) were obtained with a phase-sensitive 50 kHz bioelectrical impedance Analysis device. The classic and specific BIVA procedures, which respectively correct bioelectrical values for body height (R/H and Xc/H, ohm/m) and body geometry (Rsp and Xcsp, ohm cm), were applied. Dual energy X-ray absorptiometry was used as the reference method to assess fat-mass (FM), fat-free mass (FFM) and %FM. Deuterium dilution and bromide dilution where used as the criterion method for total body water (TBW) and extracellular water (ECW), respectively. Intracellular water (ICW) was calculated as TBW minus ECW. Results Specific bioelectrical values (Rsp, Xcsp, Zsp) were positively correlated with FM and %FM (%FM; Zsp men: r = 0.569, p Conclusions Specific BIVA turns out to be more accurate for the Analysis of %FM in athletes, while it does not correctly evaluate TBW, for which classic BIVA appears to be a suitable approach. Phase angles, and hence both BIVA approaches, can detect ECW/ICW changes.
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bioelectrical impedance Vector Analysis biva for the assessment of two compartment body composition
European Journal of Clinical Nutrition, 2014Co-Authors: Roberto Buffa, Elena Mereu, Ornella Comandini, Me Ibanez, Elisabetta MariniAbstract:This review is directed to define the efficacy of bioelectrical impedance Vector Analysis (BIVA) for assessing two-compartment body composition. A systematic literature review using MEDLINE database up to 12 February 2014 was performed. The list of papers citing the first description of BIVA, obtained from SCOPUS, and the reference lists of included studies were also searched. Selection criteria included studies comparing the results of BIVA with those of other techniques, and studies analyzing bioelectrical Vectors of obese, athletic, cachectic and lean individuals. Thirty articles met the inclusion criteria. The ability of classic BIVA for assessing two-compartment body composition has been mainly evaluated by means of indirect techniques, such as anthropometry and bioelectrical impedance Analysis (BIA). Classic BIVA showed a high agreement with body mass index, that can be interpreted in relation to the greater body mass of obese and athletic individuals, whereas the comparison with BIA showed less consistent results, especially in diseased individuals. When a reference method was used, classic BIVA failed to accurately recognize FM% variations, whereas specific BIVA furnished good results. Specific BIVA is a promising alternative to classic BIVA for assessing two-compartment body composition, with potential application in nutritional, sport and geriatric medicine.
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efficacy of specific bioelectrical impedance Vector Analysis biva for assessing body composition in the elderly
Journal of Nutrition Health & Aging, 2013Co-Authors: Elisabetta Marini, Bruno Saragat, Alessandra Coin, Enzo Manzato, G Sergi, Valeria Succa, Silvia Sarti, Roberto BuffaAbstract:Objectives This study aimed to ascertain the efficacy of bioelectrical impedance Vector Analysis (BIVA) in assessing body composition in the elderly by comparing findings with the results of dual-energy X-ray absorptiometry (DXA), and to test an analytical variant of the method (specific BIVA).
Tommy C. Y. Chan - One of the best experts on this subject based on the ideXlab platform.
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Vector Analysis of high 3 diopters astigmatism correction using small incision lenticule extraction and laser in situ keratomileusis
Journal of Cataract and Refractive Surgery, 2018Co-Authors: Tommy C. Y. Chan, Alex L K Ng, Vishal Jhanji, Yan Wang, Jiamei Zhang, Marco Yu, George P M ChengAbstract:Purpose To compare the astigmatic correction in high myopic astigmatism between small-incision lenticule extraction and laser in situ keratomileusis (LASIK) using Vector Analysis. Setting Hong Kong Laser Eye Center, Hong Kong. Design Retrospective case series. Methods Patients who had correction of myopic astigmatism of 3.0 diopters (D) or more and had either small-incision lenticule extraction or femtosecond laser–assisted LASIK were included. Only the left eye was included for Analysis. Visual and refractive results were presented and compared between groups. Results The study comprised 105 patients (40 eyes in the small-incision lenticule extraction group and 65 eyes in the femtosecond laser–assisted LASIK group.) The mean preoperative manifest cylinder was −3.42 D ± 0.55 (SD) in the small-incision lenticule extraction group and −3.47 ± 0.49 D in the LASIK group (P = .655). At 3 months, there was no significant between-group difference in uncorrected distance visual acuity (P = .915) and manifest spherical equivalent (P = .145). Ninety percent and 95.4% of eyes were within ± 0.5 D of the attempted cylindrical correction for the small-incision lenticule extraction and LASIK group, respectively (P = .423). Vector Analysis showed comparable target-induced astigmatism (P = .709), surgically induced astigmatism Vector (P = .449), difference Vector (P = .335), and magnitude of error (P = .413) between groups. The absolute angle of error was 1.88 ± 2.25 degrees in the small-incision lenticule extraction group and 1.37 ± 1.58 degrees in the LASIK group (P = .217). Conclusion Small-incision lenticule extraction offered astigmatic correction comparable to LASIK in eyes with high myopic astigmatism.
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Vector Analysis of astigmatic correction after small incision lenticule extraction and femtosecond assisted lasik for low to moderate myopic astigmatism
British Journal of Ophthalmology, 2016Co-Authors: George P M Cheng, Alex L K Ng, Tommy C. Y. Chan, Vishal Jhanji, Cong Ye, Clement C Y Tham, Zheng WangAbstract:Aim To compare astigmatic correction between femtosecond-assisted laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). Methods A total of 111 patients were included in this prospective study. Fifty-seven eyes were treated with LASIK and 54 eyes were treated with SMILE for myopia with low to moderate (−0.25 to −4.0 D) astigmatism. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity and manifest refraction were measured preoperatively and at 1 and 3 months postoperatively. Visual and refractive outcomes were reported. Changes in refractive astigmatism were evaluated using Vector Analysis. Results Preoperative characteristics were similar between both groups. The UDVA at 1 and 3 months was better in the LASIK group compared with the SMILE group (p 0.596) between the two groups. Surgically induced astigmatism was significantly lower in the SMILE group (p 0.122). Conclusions Our results showed that SMILE offered a less favourable astigmatic correction comparable to femtosecond-assisted LASIK in eyes with low to moderate myopic astigmatism. The alignment of treatment was more variable in SMILE, leading to a lower efficacy compared with LASIK by 3 months postoperatively.
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Vector Analysis of corneal astigmatism after combined femtosecond assisted phacoemulsification and arcuate keratotomy
American Journal of Ophthalmology, 2015Co-Authors: George P M Cheng, Tommy C. Y. Chan, Vishal Jhanji, Clement C Y Tham, Zheng Wang, Victor C P WooAbstract:Purpose To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. Design Retrospective, interventional case series. Methods This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector Analysis of the astigmatic changes was performed using the Alpins method. Results Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively ( P Conclusions Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies.
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Vector Analysis of corneal astigmatism after combined femtosecond assisted phacoemulsification and arcuate keratotomy
American Journal of Ophthalmology, 2015Co-Authors: George P M Cheng, Tommy C. Y. Chan, Vishal Jhanji, Clement C Y Tham, Zheng WangAbstract:PURPOSE: To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. DESIGN: Retrospective, interventional case series. METHODS: This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector Analysis of the astigmatic changes was performed using the Alpins method. RESULTS: Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively (P < .001). The magnitude of error (difference between surgically induced and target-induced astigmatism) (-0.13 ± 0.68 D), as well as the correction index (ratio of surgically induced and target-induced astigmatism) (0.86 ± 0.52), demonstrated slight undercorrection. The angle of error was very close to 0, indicating no significant systematic error of misaligned treatment. However, the absolute angle of error showed a less favorable range (17.5 ± 19.2 degrees), suggesting variable factors such as healing or alignment at an individual level. There were no intraoperative or postoperative complications. CONCLUSIONS: Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies.
