Massachusetts General HospitalStandard MRI machines create a magneticfield that orients the hydrogen within body tissues’ water molecules in one direction.
麻省总医院标准的MRI机器能纸草一个磁场，让人体细胞内所有水分子中的氢朝向一个方向。
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It sums up the definition, general expressing formula and general calculating method of flux in any vector field by analyzing the flux in the speed field, electric field and magnetic field of fluid.
A general method for designing magneticfield gradient coils on a cylindrical surface with an axial magnetic field to be used in NMR imaging is suggested and developed.