The Experts below are selected from a list of 27414 Experts worldwide ranked by ideXlab platform
Yanmin Yang - One of the best experts on this subject based on the ideXlab platform.
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efficient upconversion luminescence from ba5gd8zn4o21 yb3 er3 based on a demonstrated Cross Relaxation process
Scientific Reports, 2016Co-Authors: Chao Mi, Jianhong Wu, Yanmin YangAbstract:Efficient upconversion luminescence from Ba 5 Gd 8 Zn 4 O 21 :Yb 3+ , Er 3+ based on a demonstrated Cross-Relaxation process
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efficient upconversion luminescence from ba5gd8zn4o21 yb3 er3 based on a demonstrated Cross Relaxation process
Scientific Reports, 2016Co-Authors: Yanmin Yang, Boning Han, Jun WeiAbstract:Under 971 nm excitation, bright green and red emissions from Yb(3+)/Er(3+) co-doped Ba5Gd8Zn4O21 phosphor can be observed, especially the intense red emission in highly doped samples. The experimental results indicate that Ba5Gd8Zn4O21:Yb(3+), Er(3+) emits stronger upconversion luminescence than NaYF4:Yb(3+), Er(3+) under a low excitation power, and a maximum upconversion power efficiency of 2.7% for Ba5Gd8Zn4O21:Yb(3+), Er(3+) was achieved. More significantly, to explain the red emission enhanced with the dopant concentration, this paper presents a possible Cross-Relaxation process and demonstrates it based on the rate equation description and temporal evolution. In view of the strong upconversion luminescence, colour tunable ability and stable chemical nature, Yb(3+)/Er(3+) co-doped Ba5Gd8Zn4O21 phosphor could be an excellent candidate for efficient upconversion luminescence generation.
Vasily L Yarnykh - One of the best experts on this subject based on the ideXlab platform.
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analysis and correction of biases in Cross Relaxation mri due to biexponential longitudinal Relaxation
Magnetic Resonance in Medicine, 2014Co-Authors: Pouria Mossahebi, Vasily L Yarnykh, Alexey SamsonovAbstract:Purpose Cross-Relaxation imaging (CRI) is a family of quantitative magnetization transfer techniques that utilize images obtained with off-resonance saturation and longitudinal Relaxation rate (R1) maps reconstructed by the variable flip angle (VFA) method. It was demonstrated recently that a significant bias in an apparent VFA R1 estimation occurs in macromolecule-rich tissues due to magnetization transfer (MT)-induced biexponential behavior of longitudinal Relaxation of water protons. The purpose of this article is to characterize theoretically and experimentally the resulting bias in the CRI maps and propose methods to correct it. Theory The modified CRI algorithm is proposed, which corrects for such biases and yields accurate parametric bound pool fraction f, Cross-Relaxation rate k, and R1 maps. Additionally, an analytical correction procedure is introduced to recalculate previously obtained parameter values. Results The systematic errors due to unaccounted MT-induced biexponential Relaxation can be characterized as an overestimation of R1, f, and k, with a relative bias comparable with the magnitude of f. The phantom and human in vivo experiments demonstrate that both proposed modified CRI and analytical correction approaches significantly improve the accuracy of the CRI method. Conclusion The accuracy of the CRI method can be considerably improved by taking into account the contribution of MT-induced biexponential longitudinal Relaxation into variable flip angle R1 measurements. Magn Reson Med 71:830–838, 2014. © 2013 Wiley Periodicals, Inc.
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direct quantitative comparison between Cross Relaxation imaging and diffusion tensor imaging of the human brain at 3 0 t
NeuroImage, 2009Co-Authors: Hunter R Underhill, Chun Yuan, Vasily L YarnykhAbstract:Abstract Cross-Relaxation imaging (CRI) describes the magnetization transfer within tissues between mobile water protons and macromolecular protons. Whole-brain parametric maps of the principle kinetic components of magnetization transfer, the fraction of macromolecular protons ( f ) and the rate constant ( k ), revealed detailed anatomy of white matter (WM) fiber tracts at 1.5 T. In this study, CRI was first adapted to 3.0 T, and constraints for transverse Relaxation times of water and macromolecular protons were identified to enable unbiased f and k estimation. Subsequently, whole-brain CRI and diffusion tensor imaging (DTI) were performed in five healthy subjects. The parameters f and k were compared to DTI indices (fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity (RD), and axial diffusivity (AD)) aCross a range of anatomic regions. In WM, neither f nor k was significantly correlated to FA, RD, and AD. In contrast, both f ( r = 0.90 and r = − 0.80) and k ( r = 0.92 and r = − 0.89) in gray matter (GM) were strongly correlated to FA and RD, respectively. A moderate correlation between ADC and k ( r = 0.48) was identified in WM, while an inverse correlation was identified in GM ( r = − 0.72). The lack of association between CRI and FA in WM is consistent with differences in the underlying physical principles between techniques — fiber density vs. directionality, respectively. The association in GM may be attributable to variable axonal density unique to each structure. Our findings suggest that whole-brain CRI provides distinct quantitative information compared to DTI, and CRI parameters may prove constructive as biomarkers in neurological diseases.
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Cross Relaxation imaging reveals detailed anatomy of white matter fiber tracts in the human brain
NeuroImage, 2004Co-Authors: Vasily L Yarnykh, Chun YuanAbstract:Abstract Cross-Relaxation imaging is a new quantitative MRI modality, which allows mapping of fundamental parameters determining the magnetization transfer (MT) effect in tissues, Cross-Relaxation rate constant ( k ) and bound pool fraction ( f ). This study introduces a new time-efficient technique for Cross-Relaxation imaging, which obtains three-dimensional (3D) whole-brain k and f maps with scan time of R 1 (=1 / T 1 ) map. Anatomical correlations of in vivo Cross-Relaxation parametric maps were evaluated in three healthy subjects. The f maps revealed correspondence of areas with highly elevated f = 12–15% to major fiber tracts such as corpus callosum, anterior commissure, optic radiations, and major brain fasciculi. The rest of white matter (WM) demonstrated lower f = 9–11%, resulting in clear visual contrast of fiber tracts. Even lower f = 6.5–8.5% were found in gray matter (GM) with the highest f = 8.5% in the anterior thalamus. Distribution of k was relatively uniform in WM and produced sharp contrast between GM and WM ( k = 1.6 and 3.3 s −1 , respectively). The most marked feature of k maps was their ability to visualize the corticospinal tract, which had elevated k = 3.4–3.8 s −1 but appeared invisible on f maps. The observed patterns on f maps can be explained by variations in the density of myelinated fibers, while the trends of k may reflect regional differences in axonal organization. Cross-Relaxation imaging can be used in various clinical studies focused on brain development and white matter diseases.
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Cross Relaxation imaging reveals detailed anatomy of white matter fiber tracts in the human brain
NeuroImage, 2004Co-Authors: Vasily L Yarnykh, Chun YuanAbstract:Cross-Relaxation imaging is a new quantitative MRI modality, which allows mapping of fundamental parameters determining the magnetization transfer (MT) effect in tissues, Cross-Relaxation rate constant (k) and bound pool fraction (f). This study introduces a new time-efficient technique for Cross-Relaxation imaging, which obtains three-dimensional (3D) whole-brain k and f maps with scan time of <30 min and isotropic spatial resolution of 1.4 mm. The technical principle of the method is based on four-point fit of a matrix model of pulsed MT to imaging data obtained with variable offset frequency saturation while using a complimentary R1 (=1 / T1) map. Anatomical correlations of in vivo Cross-Relaxation parametric maps were evaluated in three healthy subjects. The f maps revealed correspondence of areas with highly elevated f = 12-15% to major fiber tracts such as corpus callosum, anterior commissure, optic radiations, and major brain fasciculi. The rest of white matter (WM) demonstrated lower f = 9-11%, resulting in clear visual contrast of fiber tracts. Even lower f = 6.5-8.5% were found in gray matter (GM) with the highest f = 8.5% in the anterior thalamus. Distribution of k was relatively uniform in WM and produced sharp contrast between GM and WM (k = 1.6 and 3.3 s(-1), respectively). The most marked feature of k maps was their ability to visualize the corticospinal tract, which had elevated k = 3.4-3.8 s(-1) but appeared invisible on f maps. The observed patterns on f maps can be explained by variations in the density of myelinated fibers, while the trends of k may reflect regional differences in axonal organization. Cross-Relaxation imaging can be used in various clinical studies focused on brain development and white matter diseases.
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pulsed z spectroscopic imaging of Cross Relaxation parameters in tissues for human mri theory and clinical applications
Magnetic Resonance in Medicine, 2002Co-Authors: Vasily L YarnykhAbstract:A new method of pulsed Z-spectroscopic imaging is proposed for in vivo visualization and quantification of the parameters describing Cross-Relaxation between protons with liquid-like and solid-like Relaxation properties in tissues. The method is based on analysis of the magnetization transfer (MT) effect as a function of the offset frequency and amplitude of a pulsed off- resonance saturation incorporated in a spoiled gradient-echo MRI pulse sequence. The theoretical concept of the method relies on an approximated analytical model of pulsed MT that provides a simple three-parameter equation for a pulsed steady-state Z-spectrum taken far from resonance. Using this model, the parametric images of Cross-Relaxation rate constant, content, and T2 of the semisolid proton fraction can be reconstructed from a series of MT-weighted images and a coregistered T1 map. The method was implemented on a 0.5 T clinical MRI scanner, and it provided high-quality 3D parametric maps within an acceptable scanning time. The estimates of Cross-Relaxation parameters in brain tissues were shown to be quantitatively consistent with the literature data. Clinical examples of the parametric images of human brain pathologies (multiple sclerosis and glioma) demonstrated high tissue contrast and clear visualization of the lesions. Magn Reson Med 47:929–939, 2002. © 2002 Wiley-Liss, Inc.
Balaji Srinivasan - One of the best experts on this subject based on the ideXlab platform.
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high power 400 mw diode pumped 2 7 micro sign m er zblan fibre lasers using enhanced er er Cross Relaxation processes
Electronics Letters, 1999Co-Authors: Balaji Srinivasan, E Poppe, J Tafoya, Ravinder K JainAbstract:The authors report the use of enhanced inter-ion Cross-Relaxation in Er:ZBLAN fibres of double clad geometries for the realisation of high-power (400 mW) diode-pumped 2.7 /spl mu/m lasers. The enhanced Er-Er Cross-Relaxation was enabled by the formation of clusters, around drawing-induced defects, even at moderate mean doping densities in such fibres. Further extension of this work should enable multi-Watt CW power level lasers at 2.7 /spl mu/m in the foreseeable future.
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high power watt level cw operation of diode pumped 2 7 μm fiber lasers using efficient Cross Relaxation and energy transfer mechanisms
Optics Express, 1999Co-Authors: Balaji Srinivasan, J Tafoya, Ravi JainAbstract:We report the demonstration of high power (660 mW) CW operation of a diode-pumped mid-IR Er fiber laser. This was achieved by using efficient depopulation of the lower laser level via enhanced Cross-Relaxation between Er ions and energy transfer to Pr ions (at doping densities much higher than those used previously in Er:ZBLAN), along with optimal pumping of such lasers via custom-designed double-clad fluoride fibers.
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high power watt level cw operation of diode pumped 2 7 aem fiber lasers using efficient Cross Relaxation and energy transfer mechanisms
Optics Express, 1999Co-Authors: Balaji Srinivasan, J Tafoya, Ravinder K JainAbstract:We report the demonstration of high power (660 mW) CW operation of a diode-pumped mid-IR Er fiber laser. This was achieved by using efficient depopulation of the lower laser level via enhanced Cross-Relaxation between Er ions and energy transfer to Pr ions (at doping densities much higher than those used previously in Er:ZBLAN), along with optimal pumping of such lasers via custom-designed double-clad fluoride fibers.
Chun Yuan - One of the best experts on this subject based on the ideXlab platform.
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direct quantitative comparison between Cross Relaxation imaging and diffusion tensor imaging of the human brain at 3 0 t
NeuroImage, 2009Co-Authors: Hunter R Underhill, Chun Yuan, Vasily L YarnykhAbstract:Abstract Cross-Relaxation imaging (CRI) describes the magnetization transfer within tissues between mobile water protons and macromolecular protons. Whole-brain parametric maps of the principle kinetic components of magnetization transfer, the fraction of macromolecular protons ( f ) and the rate constant ( k ), revealed detailed anatomy of white matter (WM) fiber tracts at 1.5 T. In this study, CRI was first adapted to 3.0 T, and constraints for transverse Relaxation times of water and macromolecular protons were identified to enable unbiased f and k estimation. Subsequently, whole-brain CRI and diffusion tensor imaging (DTI) were performed in five healthy subjects. The parameters f and k were compared to DTI indices (fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity (RD), and axial diffusivity (AD)) aCross a range of anatomic regions. In WM, neither f nor k was significantly correlated to FA, RD, and AD. In contrast, both f ( r = 0.90 and r = − 0.80) and k ( r = 0.92 and r = − 0.89) in gray matter (GM) were strongly correlated to FA and RD, respectively. A moderate correlation between ADC and k ( r = 0.48) was identified in WM, while an inverse correlation was identified in GM ( r = − 0.72). The lack of association between CRI and FA in WM is consistent with differences in the underlying physical principles between techniques — fiber density vs. directionality, respectively. The association in GM may be attributable to variable axonal density unique to each structure. Our findings suggest that whole-brain CRI provides distinct quantitative information compared to DTI, and CRI parameters may prove constructive as biomarkers in neurological diseases.
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Cross Relaxation imaging reveals detailed anatomy of white matter fiber tracts in the human brain
NeuroImage, 2004Co-Authors: Vasily L Yarnykh, Chun YuanAbstract:Abstract Cross-Relaxation imaging is a new quantitative MRI modality, which allows mapping of fundamental parameters determining the magnetization transfer (MT) effect in tissues, Cross-Relaxation rate constant ( k ) and bound pool fraction ( f ). This study introduces a new time-efficient technique for Cross-Relaxation imaging, which obtains three-dimensional (3D) whole-brain k and f maps with scan time of R 1 (=1 / T 1 ) map. Anatomical correlations of in vivo Cross-Relaxation parametric maps were evaluated in three healthy subjects. The f maps revealed correspondence of areas with highly elevated f = 12–15% to major fiber tracts such as corpus callosum, anterior commissure, optic radiations, and major brain fasciculi. The rest of white matter (WM) demonstrated lower f = 9–11%, resulting in clear visual contrast of fiber tracts. Even lower f = 6.5–8.5% were found in gray matter (GM) with the highest f = 8.5% in the anterior thalamus. Distribution of k was relatively uniform in WM and produced sharp contrast between GM and WM ( k = 1.6 and 3.3 s −1 , respectively). The most marked feature of k maps was their ability to visualize the corticospinal tract, which had elevated k = 3.4–3.8 s −1 but appeared invisible on f maps. The observed patterns on f maps can be explained by variations in the density of myelinated fibers, while the trends of k may reflect regional differences in axonal organization. Cross-Relaxation imaging can be used in various clinical studies focused on brain development and white matter diseases.
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Cross Relaxation imaging reveals detailed anatomy of white matter fiber tracts in the human brain
NeuroImage, 2004Co-Authors: Vasily L Yarnykh, Chun YuanAbstract:Cross-Relaxation imaging is a new quantitative MRI modality, which allows mapping of fundamental parameters determining the magnetization transfer (MT) effect in tissues, Cross-Relaxation rate constant (k) and bound pool fraction (f). This study introduces a new time-efficient technique for Cross-Relaxation imaging, which obtains three-dimensional (3D) whole-brain k and f maps with scan time of <30 min and isotropic spatial resolution of 1.4 mm. The technical principle of the method is based on four-point fit of a matrix model of pulsed MT to imaging data obtained with variable offset frequency saturation while using a complimentary R1 (=1 / T1) map. Anatomical correlations of in vivo Cross-Relaxation parametric maps were evaluated in three healthy subjects. The f maps revealed correspondence of areas with highly elevated f = 12-15% to major fiber tracts such as corpus callosum, anterior commissure, optic radiations, and major brain fasciculi. The rest of white matter (WM) demonstrated lower f = 9-11%, resulting in clear visual contrast of fiber tracts. Even lower f = 6.5-8.5% were found in gray matter (GM) with the highest f = 8.5% in the anterior thalamus. Distribution of k was relatively uniform in WM and produced sharp contrast between GM and WM (k = 1.6 and 3.3 s(-1), respectively). The most marked feature of k maps was their ability to visualize the corticospinal tract, which had elevated k = 3.4-3.8 s(-1) but appeared invisible on f maps. The observed patterns on f maps can be explained by variations in the density of myelinated fibers, while the trends of k may reflect regional differences in axonal organization. Cross-Relaxation imaging can be used in various clinical studies focused on brain development and white matter diseases.
Ravi Jain - One of the best experts on this subject based on the ideXlab platform.
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high power watt level cw operation of diode pumped 2 7 μm fiber lasers using efficient Cross Relaxation and energy transfer mechanisms
Optics Express, 1999Co-Authors: Balaji Srinivasan, J Tafoya, Ravi JainAbstract:We report the demonstration of high power (660 mW) CW operation of a diode-pumped mid-IR Er fiber laser. This was achieved by using efficient depopulation of the lower laser level via enhanced Cross-Relaxation between Er ions and energy transfer to Pr ions (at doping densities much higher than those used previously in Er:ZBLAN), along with optimal pumping of such lasers via custom-designed double-clad fluoride fibers.