Bottomley P A, Andrew E R
Phys Med Biol. 1978 Jul;23(4):630-43. doi: 10.1088/0031-9155/23/4/006.
The magnetic field penetration, phase shift and power deposition in planar and cylindrical models of biological tissue exposed to a sinusoidal time-dependent magnetic field have been investigated theoretically over the frequency range 1 to 100 MHz. The results are based on measurements of the relative permittivity and resistivity dispersions of a variety of freshly excised rat tissue at 37 and 25 degrees C, and are analysed in terms of their implications for human body nuclear magnetic resonance (NMR) imaging. The results indicate that at NMR operating frequencies much greater than about 30 MHz, magnetic field amplitude and phase variations experienced by the nuclei may cause serious distortions in an image of a human torso. The maximum power deposition envisaged during an NMR imaging experiment on a human torso is likely to be comparable to existing long-term safe exposure levels, and will depend ultimately on the imaging technique and NMR frequency employed.
理论上研究了在1至100MHz频率范围内，暴露于随时间呈正弦变化磁场中的生物组织平面和圆柱模型中的磁场穿透、相移和功率沉积。结果基于对多种新鲜切除的大鼠组织在37摄氏度和25摄氏度下相对介电常数和电阻率色散的测量，并根据其对人体核磁共振（NMR）成像的影响进行分析。结果表明，在远高于约30MHz的NMR工作频率下，原子核所经历的磁场幅度和相位变化可能会导致人体躯干图像出现严重失真。在人体躯干上进行NMR成像实验时设想的最大功率沉积可能与现有的长期安全暴露水平相当，并且最终将取决于所采用的成像技术和NMR频率。
