Saturation Magnetization

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Akihisa Inoue - One of the best experts on this subject based on the ideXlab platform.

  • new fe based soft magnetic amorphous alloys with high Saturation Magnetization and good corrosion resistance for dust core application
    Intermetallics, 2016
    Co-Authors: F L Kong, Elsayed Shalaan, Akihisa Inoue, F Almarzouki
    Abstract:

    Abstract Fe-rich amorphous dust core alloys with minor-addition of Mo and/or Cr were synthesized because of the industrial request of mass production of high efficient low core loss Fe-based dust cores. It was found that the present Fe-(Cr, Mo)-P-B-Si-(C) amorphous alloy ribbons exhibit good soft magnetic properties of above 1.5 T for Saturation Magnetization, below 10 A/m for coercivity and rather good corrosion resistance in 3%NaCl aqueous solution. Besides, the amorphous alloy ribbons exhibit good bending ductility in as-spun and optimally annealed states. It is noticed that these characteristics are much superior to those for commercial Fe-Cr-Nb-P-B-Si soft magnetic dust core alloy (SENNTIX). In addition, the annealing treatment was noticed to cause the improvement of corrosion resistance without detriment to bending ductility. The new Fe-based soft magnetic alloys with good combined characteristics are expected to be used as the basic material as high-efficient soft magnetic dust cores in a high frequency range.

  • softening and good ductility for nanocrystal dispersed amorphous fe co b alloys with high Saturation Magnetization above 1 7 t
    Journal of Alloys and Compounds, 2016
    Co-Authors: Y D Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, S L Shu, F Almarzouki
    Abstract:

    Abstract Fe 80−x Co 20 B x (x = 12–15 at%) alloy ribbons consisting of single bcc phase (12%B), amorphous plus bcc-Fe(Co) mixed phases (13%B) and amorphous single phase (14%B and 15%B) were synthesized by the melt-spinning technique. It is noticed that all the alloy ribbons containing amorphous phase exhibit good bending ductility in the as-spun state and even after annealing which leads to the precipitation of nanoscale bcc-Fe(Co) phase. The amorphous plus bcc-Fe(Co) phase alloys with lower hardness exhibited a number of microcracks in the region near the hardness indentation trace, in addition to distinct slip step markings. The decrease in hardness and the maintenance of ductility in the nanocrystalline state are interpreted to originate from microcrack-induced softening phenomenon. The nanocrystalline alloys also exhibit good soft magnetic properties with high Saturation Magnetization above 1.7 T in combination with low coercivity of about 20 A/m. The good bending ductility as well as the microcrack-induced softening for the amorphous alloys including nanoscale bcc-Fe(Co) phase is believed to be the first evidence in the long development history of Fe-based nanocrystalline soft magnetic alloys. The finding of the ductile Fe-based nanocrystalline alloys with high Saturation Magnetization is encouraging for further extension of nanocrystalline magnetic materials.

  • syntheses and corrosion behaviors of fe based amorphous soft magnetic alloys with high Saturation Magnetization near 1 7 t
    Journal of Materials Research, 2015
    Co-Authors: Ye Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, Shengli Zhu, F Almarzouki
    Abstract:

    Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-Saturation Magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-Saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.

  • fe based amorphous soft magnetic alloys with high Saturation Magnetization and good bending ductility
    Journal of Alloys and Compounds, 2014
    Co-Authors: F L Kong, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, F Almarzouki
    Abstract:

    Fe-based amorphous alloys with high Saturation Magnetization up to 1.7 T were synthesized in Fe-B-Si-P alloy system. The amorphous alloys exhibit good soft magnetic properties, such as low coercive force of 3.3-6.2 A/m and high effective permeability of 8300-15,000. In additional, the present alloys show good bending ductility, even in an annealed state. The combination of good magnetic and mechanical properties makes them promising candidates as magnetic functional materials in the future. (C) 2014 Elsevier B.V. All rights reserved.

  • fe based soft magnetic amorphous alloys with high Saturation Magnetization above 1 5 t and high corrosion resistance
    Intermetallics, 2014
    Co-Authors: Ye Han, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, Shengli Zhu, D V Louzguineluzgin, F Almarzouki
    Abstract:

    Abstract Fe-rich amorphous alloys with minor-addition of Cr and/or Nb were examined with the aim of developing Fe-based amorphous alloys exhibiting simultaneously high Saturation Magnetization above 1.5 T and good corrosion properties. Fe82Cr2B8P4Si3C and Fe82NbB9P4Si3C amorphous alloys were found to exhibit high Saturation Magnetizations of 1.49 T and 1.57 T, respectively, and rather good corrosion resistance in 3.5 mass% NaCl solution at 298 K. The minor-addition of Cr or Nb enables the formation of amorphous alloy particles without harmful oxide layer by water atomization process which makes these alloys suitable for applications as soft magnetic core materials. The addition of 1 at% Nb improved the corrosion resistance through the increase in Ecorr value, which makes easy to reach passive state, and the suppression of pitting corrosion. Besides, it has been proved that the simultaneous addition of Nb and Cr has an effect on forming protective passive film.

F Almarzouki - One of the best experts on this subject based on the ideXlab platform.

  • new fe based soft magnetic amorphous alloys with high Saturation Magnetization and good corrosion resistance for dust core application
    Intermetallics, 2016
    Co-Authors: F L Kong, Elsayed Shalaan, Akihisa Inoue, F Almarzouki
    Abstract:

    Abstract Fe-rich amorphous dust core alloys with minor-addition of Mo and/or Cr were synthesized because of the industrial request of mass production of high efficient low core loss Fe-based dust cores. It was found that the present Fe-(Cr, Mo)-P-B-Si-(C) amorphous alloy ribbons exhibit good soft magnetic properties of above 1.5 T for Saturation Magnetization, below 10 A/m for coercivity and rather good corrosion resistance in 3%NaCl aqueous solution. Besides, the amorphous alloy ribbons exhibit good bending ductility in as-spun and optimally annealed states. It is noticed that these characteristics are much superior to those for commercial Fe-Cr-Nb-P-B-Si soft magnetic dust core alloy (SENNTIX). In addition, the annealing treatment was noticed to cause the improvement of corrosion resistance without detriment to bending ductility. The new Fe-based soft magnetic alloys with good combined characteristics are expected to be used as the basic material as high-efficient soft magnetic dust cores in a high frequency range.

  • softening and good ductility for nanocrystal dispersed amorphous fe co b alloys with high Saturation Magnetization above 1 7 t
    Journal of Alloys and Compounds, 2016
    Co-Authors: Y D Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, S L Shu, F Almarzouki
    Abstract:

    Abstract Fe 80−x Co 20 B x (x = 12–15 at%) alloy ribbons consisting of single bcc phase (12%B), amorphous plus bcc-Fe(Co) mixed phases (13%B) and amorphous single phase (14%B and 15%B) were synthesized by the melt-spinning technique. It is noticed that all the alloy ribbons containing amorphous phase exhibit good bending ductility in the as-spun state and even after annealing which leads to the precipitation of nanoscale bcc-Fe(Co) phase. The amorphous plus bcc-Fe(Co) phase alloys with lower hardness exhibited a number of microcracks in the region near the hardness indentation trace, in addition to distinct slip step markings. The decrease in hardness and the maintenance of ductility in the nanocrystalline state are interpreted to originate from microcrack-induced softening phenomenon. The nanocrystalline alloys also exhibit good soft magnetic properties with high Saturation Magnetization above 1.7 T in combination with low coercivity of about 20 A/m. The good bending ductility as well as the microcrack-induced softening for the amorphous alloys including nanoscale bcc-Fe(Co) phase is believed to be the first evidence in the long development history of Fe-based nanocrystalline soft magnetic alloys. The finding of the ductile Fe-based nanocrystalline alloys with high Saturation Magnetization is encouraging for further extension of nanocrystalline magnetic materials.

  • syntheses and corrosion behaviors of fe based amorphous soft magnetic alloys with high Saturation Magnetization near 1 7 t
    Journal of Materials Research, 2015
    Co-Authors: Ye Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, Shengli Zhu, F Almarzouki
    Abstract:

    Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-Saturation Magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-Saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.

  • fe based amorphous soft magnetic alloys with high Saturation Magnetization and good bending ductility
    Journal of Alloys and Compounds, 2014
    Co-Authors: F L Kong, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, F Almarzouki
    Abstract:

    Fe-based amorphous alloys with high Saturation Magnetization up to 1.7 T were synthesized in Fe-B-Si-P alloy system. The amorphous alloys exhibit good soft magnetic properties, such as low coercive force of 3.3-6.2 A/m and high effective permeability of 8300-15,000. In additional, the present alloys show good bending ductility, even in an annealed state. The combination of good magnetic and mechanical properties makes them promising candidates as magnetic functional materials in the future. (C) 2014 Elsevier B.V. All rights reserved.

  • fe based soft magnetic amorphous alloys with high Saturation Magnetization above 1 5 t and high corrosion resistance
    Intermetallics, 2014
    Co-Authors: Ye Han, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, Shengli Zhu, D V Louzguineluzgin, F Almarzouki
    Abstract:

    Abstract Fe-rich amorphous alloys with minor-addition of Cr and/or Nb were examined with the aim of developing Fe-based amorphous alloys exhibiting simultaneously high Saturation Magnetization above 1.5 T and good corrosion properties. Fe82Cr2B8P4Si3C and Fe82NbB9P4Si3C amorphous alloys were found to exhibit high Saturation Magnetizations of 1.49 T and 1.57 T, respectively, and rather good corrosion resistance in 3.5 mass% NaCl solution at 298 K. The minor-addition of Cr or Nb enables the formation of amorphous alloy particles without harmful oxide layer by water atomization process which makes these alloys suitable for applications as soft magnetic core materials. The addition of 1 at% Nb improved the corrosion resistance through the increase in Ecorr value, which makes easy to reach passive state, and the suppression of pitting corrosion. Besides, it has been proved that the simultaneous addition of Nb and Cr has an effect on forming protective passive film.

Jianping Wang - One of the best experts on this subject based on the ideXlab platform.

  • high Saturation Magnetization and low magnetic anisotropy fe cn martensite thin film
    Applied Physics Letters, 2019
    Co-Authors: Xiaowei Zhang, Jianping Wang
    Abstract:

    Fe16N2 thin films possess high Saturation Magnetization (Ms) and high magnetic crystalline anisotropy (Ku) simultaneously. For application in magnetic recording and electrical machine, soft magnetic materials with high Ms and low Ku are desirable. In this report, carbon was doped into FeN thin films. Fe-CN martensite thin films, also named “Minnealloy,” were fabricated by a facing target sputtering system. The Fe-CN martensite phase was detected by X-ray diffraction (XRD). Vibrating sample magnetometry (VSM) measurements confirmed the high Ms property even though ordered Fe-CN was not formed. An X-ray photoelectron spectroscopy study was carried out to reveal the carbon and nitrogen electronic environment. The Ku value was obtained from the M-H loop and the law to approach Saturation with reasonable consistency around 1–2 × 106 erg/cc, which is about five to ten times smaller than that of the ordered Fe16N2 thin film (1–2 × 107 erg/cc). The combination of high Ms and low Saturation fields makes the Fe-CN martensite thin film a potential candidate for the magnetic write head and other applications.

  • estimating Saturation Magnetization of superparamagnetic nanoparticles in liquid phase
    Journal of Magnetism and Magnetic Materials, 2019
    Co-Authors: Kai Wu, Diqing Su, Jianping Wang
    Abstract:

    Abstract Superparamagnetic nanoparticles (SPMNPs), with unique physical and magnetic properties that differentiate them from their bulk magnetic materials, have been widely studied for potential applications in biomedical areas. With proper surface chemical functionalization, SPMNPs have found their applications in magnetic hyperthermia therapy, magnetic bioassays, drug delivery, magnetic manipulation, etc. These applications require elaborate tuning of the physical and magnetic properties of the SPMNPs such as Saturation Magnetization M s and magnetic core size D . In this work, we present a search coil-based method to directly characterize the M s of SPMNPs in the liquid phase. The nonlinear magnetic responses of SPMNPs under oscillating magnetic fields are exploited and the induced harmonic signals are used to analyze their M s and D . Different combinations of M s and D are assumed and their harmonic ratios R are summarized. Curve fitting shows that the harmonic ratio R = 0.74 + 2.85 × 10 9 ∙ D - 4.41 ∙ M s - 1.44 , with the coefficient of determination R-square = 0.98.

  • fabrication and physical properties of fe fe4n n multilayers with high Saturation Magnetization
    AIP Advances, 2016
    Co-Authors: L Lin, Zhuangjian Zhang, Q Y Jin, Jianping Wang
    Abstract:

    [Fe/Fe4N]N multilayers with high Saturation Magnetization were prepared on MgO(200) substrate, by the DC reactive magnetron sputtering and then annealed at higher temperature. Their structural and magnetic properties were investigated. Epitaxial growth of α-Fe and γ’-Fe4N were demonstrated on MgO, and then excellent [Fe/Fe4N]N was obtained. Though the Saturation Magnetizations of the as-deposited [Fe/Fe4N]N are slightly below the average value of those of α-Fe and γ’-Fe4N, the Saturation Magnetization of the annealed [Fe(3.04 nm)/Fe4N(3.04 nm)]5 increases up to 1850 emu/cc, 32 % larger than that of α-Fe film. N atom diffusion from the γ’-Fe4N to the α-Fe layer at high temperature greatly improves the Saturation Magnetization.

  • the effect of strain induced by ag underlayer on Saturation Magnetization of partially ordered fe16n2 thin films
    Applied Physics Letters, 2013
    Co-Authors: Xiaowei Zhang, Lawrence F Allard, Meiyin Yang, Jianping Wang
    Abstract:

    Partially ordered Fe-N thin films were grown by a facing target sputtering process on the surface of a (001) Ag underlayer on MgO substrates. It was confirmed by x-ray diffraction that the Ag layer enlarged the in-plane lattice of the Fe-N thin films. Domains of the ordered α″-Fe16N2 phase within an epitaxial (001) α′-FexN phase were identified by electron diffraction and high-resolution aberration-corrected scanning transmission electron microscopy (STEM) methods. STEM dark-field and bright-field images showed the fully ordered structure of the α″-Fe16N2 at the atomic column level. High Saturation Magnetization(Ms) of 1890 emu/cc was obtained for α″-Fe16N2 on the Ag underlayer, while only 1500 emu/cc was measured for Fe-N on the Fe underlayer. The results are likely due to a tensile strain induced in the α″-Fe16N2 phase by the Ag structure at the interface.

  • fabrication of hbox fe _ 16 hbox n _ 2 films by sputtering process and experimental investigation of origin of giant Saturation Magnetization in hbox fe _ 16 hbox n _ 2
    IEEE Transactions on Magnetics, 2012
    Co-Authors: Jianping Wang, Xiaoqi Liu, C Sanchezhanke, F M F De Groot, Lawrence F Allard, Edgar Laracurzio
    Abstract:

    We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant Saturation Magnetization in Fe16N2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe16N2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe16N2+Fe8N mixture phases and high degree of N ordering, exhibit a Saturation Magnetization up to 2.68T at room temperature, which substantially exceeds the ferromagnetism limit based on the traditional band magnetism understanding. From X-ray magnetic circular Dichorism (XMCD) experiment, transport measurement and first-principle calculation based on LDA+U method, it is both experimentally and theoretically justified that the origin of giant Saturation Magnetization is correlated with the formation of highly localized 3d electron states in this Fe-N system. A large magnetocrystalline anisotropy for such a material is also discussed. Our proposed “cluster+atom” theory provides promising directions on designing novel magnetic materials with unique performances.

Chuntao Chang - One of the best experts on this subject based on the ideXlab platform.

  • softening and good ductility for nanocrystal dispersed amorphous fe co b alloys with high Saturation Magnetization above 1 7 t
    Journal of Alloys and Compounds, 2016
    Co-Authors: Y D Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, S L Shu, F Almarzouki
    Abstract:

    Abstract Fe 80−x Co 20 B x (x = 12–15 at%) alloy ribbons consisting of single bcc phase (12%B), amorphous plus bcc-Fe(Co) mixed phases (13%B) and amorphous single phase (14%B and 15%B) were synthesized by the melt-spinning technique. It is noticed that all the alloy ribbons containing amorphous phase exhibit good bending ductility in the as-spun state and even after annealing which leads to the precipitation of nanoscale bcc-Fe(Co) phase. The amorphous plus bcc-Fe(Co) phase alloys with lower hardness exhibited a number of microcracks in the region near the hardness indentation trace, in addition to distinct slip step markings. The decrease in hardness and the maintenance of ductility in the nanocrystalline state are interpreted to originate from microcrack-induced softening phenomenon. The nanocrystalline alloys also exhibit good soft magnetic properties with high Saturation Magnetization above 1.7 T in combination with low coercivity of about 20 A/m. The good bending ductility as well as the microcrack-induced softening for the amorphous alloys including nanoscale bcc-Fe(Co) phase is believed to be the first evidence in the long development history of Fe-based nanocrystalline soft magnetic alloys. The finding of the ductile Fe-based nanocrystalline alloys with high Saturation Magnetization is encouraging for further extension of nanocrystalline magnetic materials.

  • syntheses and fundamental properties of fe rich metastable phase alloys with Saturation Magnetization exceeding 1 9 t
    Materials Research-ibero-american Journal of Materials, 2015
    Co-Authors: Ye Han, F L Kong, Chuntao Chang, Shengli Zhu, S V Ketov, Dmitri V Louzguine, Akinisa Inoue
    Abstract:

    A melt-spun Fe90Si5B5 alloy ribbon consists of bcc-Fe(Si) + Fe3B + amorphous phase and exhibits good bending ductility, high tensile fracture strength above 1000 MPa, high corrosion resistance and unique magnetic properties as exemplified for high Saturation Magnetization exceeding 1.9 T, moderately high initial permeability of about 150 and low coercivity of 745 A/m which are attractive for magnetic sensors utilizing a nearly constant high permeability with applied field up to coercivity. Besides, the tensile fracture strength and elongation increase significantly to 1286 MPa and 0.62%, respectively, after annealing for 900 s at 823 K. The Fe-Si-B alloy ribbons are attractive as a new type of sensor material with features of high bending ductility, high tensile strength and elongation, relatively good corrosion resistanceand unique soft magnetic properties with very high Saturation Magnetization.

  • syntheses and corrosion behaviors of fe based amorphous soft magnetic alloys with high Saturation Magnetization near 1 7 t
    Journal of Materials Research, 2015
    Co-Authors: Ye Han, Elsayed Shalaan, F L Kong, Akihisa Inoue, Chuntao Chang, Shengli Zhu, F Almarzouki
    Abstract:

    Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-Saturation Magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-Saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.

  • fe based amorphous soft magnetic alloys with high Saturation Magnetization and good bending ductility
    Journal of Alloys and Compounds, 2014
    Co-Authors: F L Kong, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, F Almarzouki
    Abstract:

    Fe-based amorphous alloys with high Saturation Magnetization up to 1.7 T were synthesized in Fe-B-Si-P alloy system. The amorphous alloys exhibit good soft magnetic properties, such as low coercive force of 3.3-6.2 A/m and high effective permeability of 8300-15,000. In additional, the present alloys show good bending ductility, even in an annealed state. The combination of good magnetic and mechanical properties makes them promising candidates as magnetic functional materials in the future. (C) 2014 Elsevier B.V. All rights reserved.

  • fe based soft magnetic amorphous alloys with high Saturation Magnetization above 1 5 t and high corrosion resistance
    Intermetallics, 2014
    Co-Authors: Ye Han, Elsayed Shalaan, Akihisa Inoue, Chuntao Chang, Shengli Zhu, D V Louzguineluzgin, F Almarzouki
    Abstract:

    Abstract Fe-rich amorphous alloys with minor-addition of Cr and/or Nb were examined with the aim of developing Fe-based amorphous alloys exhibiting simultaneously high Saturation Magnetization above 1.5 T and good corrosion properties. Fe82Cr2B8P4Si3C and Fe82NbB9P4Si3C amorphous alloys were found to exhibit high Saturation Magnetizations of 1.49 T and 1.57 T, respectively, and rather good corrosion resistance in 3.5 mass% NaCl solution at 298 K. The minor-addition of Cr or Nb enables the formation of amorphous alloy particles without harmful oxide layer by water atomization process which makes these alloys suitable for applications as soft magnetic core materials. The addition of 1 at% Nb improved the corrosion resistance through the increase in Ecorr value, which makes easy to reach passive state, and the suppression of pitting corrosion. Besides, it has been proved that the simultaneous addition of Nb and Cr has an effect on forming protective passive film.

Joseph V Hajnal - One of the best experts on this subject based on the ideXlab platform.

  • controlled Saturation Magnetization transfer for reproducible multivendor variable flip angle t1 and t2 mapping
    Magnetic Resonance in Medicine, 2020
    Co-Authors: Rui Pedro A G Teixeira, Radhouene Neji, Tobias C Wood, Ana A Baburamani, Shaihan J Malik, Joseph V Hajnal
    Abstract:

    PURPOSE The widespread clinical application of quantitative MRI has been hindered by a lack of reproducibility across sites and vendors. Previous work has attributed this to incorrect B1 mapping or insufficient spoiling conditions. We recently proposed the controlled Saturation Magnetization transfer (CSMT) framework and hypothesized that the lack of reproducibility can also be attributed to Magnetization transfer effects. This work seeks to validate this hypothesis and demonstrate that reproducible multivendor single-pool relaxometry can be achieved with the CSMT approach. METHODS Three healthy volunteers were scanned on scanners from 3 vendors (GE Healthcare, Philips, Siemens). An extensive set of images necessary for joint T1 and T2 estimation were acquired with (1) each vendor default RF pulses and spoiling conditions; (2) harmonized RF spoiling; and (3) harmonized RF spoiling and CSMT pulses. Different subsets of images were used to generate 6 different T1 and T2 maps for each subject's data from each vendor. Cross-protocol, cross-vendor, and test/retest variability were estimated. RESULTS Harmonized RF spoiling conditions are insufficient to ensure good cross-vendor reproducibility. Controlled Saturation Magnetization transfer allows cross-protocol variability to be reduced from 18.3% to 4.0%. Whole-brain variability using the same protocol was reduced from a maximum of 19% to 4.5% across sites. Both CSMT and native vendor RF conditions have a reported variability of less than 5% for repeat measures on the same vendor. CONCLUSION Magnetization transfer effects are a major contributor to intersite/intrasite variability of T1 and T2 estimation. Controlled Saturation Magnetization transfer stabilizes these effects, paving the way for the use of single-pool T1 and T2 as a reliable source for clinical diagnosis across sites.

  • controlled Saturation Magnetization transfer for reproducible multivendor variable flip angle t 1 and t 2 mapping
    Magnetic Resonance in Medicine, 2020
    Co-Authors: Rui Pedro A G Teixeira, Radhouene Neji, Tobias C Wood, Ana A Baburamani, Shaihan J Malik, Joseph V Hajnal
    Abstract:

    Purpose The widespread clinical application of quantitative MRI has been hindered by a lack of reproducibility across sites and vendors. Previous work has attributed this to incorrect B1 mapping or insufficient spoiling conditions. We recently proposed the controlled Saturation Magnetization transfer (CSMT) framework and hypothesized that the lack of reproducibility can also be attributed to Magnetization transfer effects. This work seeks to validate this hypothesis and demonstrate that reproducible multivendor single-pool relaxometry can be achieved with the CSMT approach. Methods Three healthy volunteers were scanned on scanners from 3 vendors (GE Healthcare, Philips, Siemens). An extensive set of images necessary for joint T1 and T2 estimation were acquired with (1) each vendor default RF pulses and spoiling conditions; (2) harmonized RF spoiling; and (3) harmonized RF spoiling and CSMT pulses. Different subsets of images were used to generate 6 different T1 and T2 maps for each subject's data from each vendor. Cross-protocol, cross-vendor, and test/retest variability were estimated. Results Harmonized RF spoiling conditions are insufficient to ensure good cross-vendor reproducibility. Controlled Saturation Magnetization transfer allows cross-protocol variability to be reduced from 18.3% to 4.0%. Whole-brain variability using the same protocol was reduced from a maximum of 19% to 4.5% across sites. Both CSMT and native vendor RF conditions have a reported variability of less than 5% for repeat measures on the same vendor. Conclusion Magnetization transfer effects are a major contributor to intersite/intrasite variability of T1 and T2 estimation. Controlled Saturation Magnetization transfer stabilizes these effects, paving the way for the use of single-pool T1 and T2 as a reliable source for clinical diagnosis across sites.

  • fast quantitative mri using controlled Saturation Magnetization transfer
    Magnetic Resonance in Medicine, 2019
    Co-Authors: Rui Pedro A G Teixeira, Shaihan J Malik, Joseph V Hajnal
    Abstract:

    Purpose This study demonstrates Magnetization transfer (MT) effects directly affect relaxometry measurements and develops a framework that allows single-pool models to be valid in 2-pool MT systems. Methods A theoretical framework is developed in which a 2-pool MT system effectively behaves as a single-pool if the RMS RF magnetic field ( B 1 rms {\text{B}}_{1}^{{{\text{rms}}}}) is kept fixed across all measurements. A practical method for achieving controlled Saturation Magnetization transfer (CSMT) using multiband RF pulses is proposed. Numerical, Phantom, and in vivo validations were performed directly comparing steady state (SS) estimation approaches that under correct single-pool assumptions would be expected to vary in precision but not accuracy. Results Numerical simulations predict single-pool estimates obtained from MT model generated data are not consistent for different SS estimation methods, and a systematic underestimation of T2 is expected. Neither effect occurs under the proposed CSMT approach. Both phantom and in vivo experiments corroborate the numerical predictions. Experimental data highlights that even when using the same relaxometry method, different estimates are obtained depending on which combination of flip angles (FAs) and TRs are used if the CSMT approach is not used. Using CSMT, stable measurements of both T1 and T2 are obtained. The measured T1 ( T 1 CSMT ) ) depends on B 1 rms {\text{B}}_{1}^{{{\text{rms}}}}, which is therefore an important parameter to specify. Conclusion This work demonstrates that conventional single pool relaxometry, which is highly efficient for human studies, results in unreliable parameter estimates in biological tissues because of MT effects. The proposed CSMT framework is shown to allow single-pool assumptions to be valid, enabling reliable and efficient quantitative imaging to be performed.