7.0 T电导率和介电常数成像
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摘要
目的磁共振电特性成像是利用磁共振成像(MRI)原始数据对被测生物组织电特性分布重建的一种方法。组织电导率和介电常数是理解磁共振成像过程中特定吸收率(SAR)的关键,这些电特性信息对于射频热疗治疗方法也很重要。由于恶性组织的电导率和相对介电常数均高于周围的健康组织,因此相关电特性也具有一定的诊断价值。方法文章使用了7.0 T的MRI发射场映像数据来计算组织的电导率和介电常数图像。磁共振谱仪得到K空间数据,包含了复数矩阵形式的自旋进度的幅度和相位信息,利用双角度法得到对应的射频场B_1~+映像。结果最终得到298 MHz下的人体头部组织的电特性图像。结论该电特性成像方法是基于中心差分方程求解磁场变化量,计算得到电导率和介电常数分布。小组制定的电导率和相对介电常数计算方法有效可行,证明电导率和相对介电常数图像能够反映不同组织电特性的对比,为磁共振电特性成像技术的实用化研究提供参考。
【Objective】Magnetic resonance imaging(MRI) is a method to reconstruct the distribution of the electrical properties of biological tissue using the original data of MRI. Tissue conductivity and permittivity are critical to understanding radio frequency(RF) power deposition during magnetic resonance imaging(MRI). These electrical properties are important to radiothermal therapy. Because the conductivity and relative dielectric constant of malignant tissue are higher than that of surrounding healthy tissue, the related electrical characteristics have certain diagnostic value.【Methods】The tissue conductivity and permittivity images were calculated using 7.0 T MRI field image data. The nuclear magnetic resonance spectrometer obtained k spatial data,including the amplitude and phase information of the spin progress in the form of complex matrix. The corresponding maps were obtained using the double angle method.【Results】Finally, the electrical characteristic image of human head tissue at 298 MHz was obtained.【Conclusion】The imaging method of electrical characteristics is based on the central difference equation to solve the variation of magnetic field and calculate the conductivity and dielectric constant distribution. The calculation method of conductivity and relative permittivity developed by the team is effective and feasible, which proves that the images of conductivity and relative permittivity can reflect the comparison of electrical properties of different tissues, providing a reference for the practical research of magnetic resonance imaging technology.
【Objective】Magnetic resonance imaging(MRI) is a method to reconstruct the distribution of the electrical properties of biological tissue using the original data of MRI. Tissue conductivity and permittivity are critical to understanding radio frequency(RF) power deposition during magnetic resonance imaging(MRI). These electrical properties are important to radiothermal therapy. Because the conductivity and relative dielectric constant of malignant tissue are higher than that of surrounding healthy tissue, the related electrical characteristics have certain diagnostic value.【Methods】The tissue conductivity and permittivity images were calculated using 7.0 T MRI field image data. The nuclear magnetic resonance spectrometer obtained k spatial data,including the amplitude and phase information of the spin progress in the form of complex matrix. The corresponding maps were obtained using the double angle method.【Results】Finally, the electrical characteristic image of human head tissue at 298 MHz was obtained.【Conclusion】The imaging method of electrical characteristics is based on the central difference equation to solve the variation of magnetic field and calculate the conductivity and dielectric constant distribution. The calculation method of conductivity and relative permittivity developed by the team is effective and feasible, which proves that the images of conductivity and relative permittivity can reflect the comparison of electrical properties of different tissues, providing a reference for the practical research of magnetic resonance imaging technology.
引文
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[15]陈思明,张雪雷.9.4 T磁共振成像系统高通鸟笼射频线圈的研制[J].电子技术应用,2017,43(7):16-18.
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[2]YEO DT,WANG Z,LOEW W,et al.Local specific absorption rate in high‐pass birdcage and transverse electromagnetic body coils for multiple human body models in clinical landmark positions at 3T[J].Journal of Magnetic Resonance Imaging,2011,33(5):1209-1217.
[3]明东,万柏坤,胡勇.肿瘤热疗及相关超声实用新技术研究进展[J].生物医学工程研究,2004(4):253-256.
[4]DAS SK,CLEGG ST,SAMULSKI TV.Computational techniques for fast hyperthermia temperature optimization[J].Medical Physics,1999,26(2):319-328.
[5]JOINES WT,ZHANG Y,LI C,et al.The measured electrical properties of normal and malignant human tissues from 50 to 900MHz[J].Medical Physics,1994,21(4):547-550.
[6]SUROWIEC AJ,STUCHLY SS,BARR JR,et al.Dielectric properties of breast carcinoma and the surrounding tissues[J].IEEETransactions on Biomedical Engineering,1988,35(4):257-263.
[7]CHENEY M,ISAACSON D,NEWELL JC.Electrical impedance tomography[J].SIAM Review,1999,41(1):85-101.
[8]SAULNIER GJ,BLUE RS,NEWELL JC,et al.Electrical impedance tomography[J].Inverse Problems,2001,18(6):31-43.
[9]KWON O,WOO EJ,YOON JR,et al.Magnetic resonance electrical impedance tomography(MREIT):simulation study of J-substitution algorithm[J].IEEE Transactions on Biomedical Engineering,2002,49(2):160-167.
[10]BULUMULLA SB,LEE SK,YEO DT.Conductivity and permittivity imaging at 3.0 T[J].Concepts in Magnetic Resonance Part B:Magnetic Resonance Engineering,2012,41(1):13-21.
[11]SACOLICK LI,WIESINGER F,HANCU I,et al.B1 mapping by Bloch-Siegert shift[J].Magnetic Resonance in Medicine,2010,63(5):1315-1322.
[12]陈艳丽.基于磁共振成像的体发射线圈的研究与设计[D].华南理工大学,2012.
[13]HOULT DI.The principle of reciprocity in signal strength calculations-a mathematical guide[J].Concepts in Magnetic Resonance 2000,12(4):173-187.
[14]PRESS WH,TEUKOLSKY SA,VETTERLING WT.Numerical recipes in C[M].New York:Cambridge University Press,2002.
[15]陈思明,张雪雷.9.4 T磁共振成像系统高通鸟笼射频线圈的研制[J].电子技术应用,2017,43(7):16-18.
[16]VAN LIER AL,BRUNNER DO,PRUESSMANN KP,et al.B1(+)phase mapping at 7 T and its application for in vivo electrical conductivity mapping[J].Magnetic Resonance in Medicine,2012,67(2):552-561.
[17]LEE S,BULLUMULA S,DIXON W,et al.B1+phase mapping for MR based electrical property measurement of a symmetric phantom[C]//Workshop MR Based Impedance Imag,2010:54.