Cantillon-Murphy P, Wald L L, Adalsteinsson E, Zahn M
Department of Gastroenterology, Brigham and Women's Hospital, Boston, MA.
J Magn Magn Mater. 2010 Mar 1;322(6):727-733. doi: 10.1016/j.jmmm.2009.10.050.
In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad/s. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4°C and 7°C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B(0). Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B(0). Results are presented for the expected temperature increase in small tumors (~1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002 to 0.01 solid volume fraction) and nanoparticle radii (1 to 10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful selection of the rotating or sinusoidal field parameters (field frequency and amplitude). The work indicates that it may be feasible to combine low-field MRI with a magnetic hyperthermia system using superparamagnetic iron oxide nanoparticles.
在交变正弦或旋转磁场存在的情况下，磁性纳米颗粒会使其磁矩与外加磁场重新对齐。这种重新对齐由纳米颗粒的时间常数τ来表征。随着磁场频率的增加，对于给定的频率Ω（单位为rad/s），纳米颗粒的磁矩会以恒定角度滞后于外加磁场。与这种失准相关的是功率耗散，它会使磁性流体的整体温度升高，这已被用作磁性纳米颗粒热疗的一种方法，特别适用于低灌注组织（如乳腺）中的癌症，在体内环境温度之上4°C至7°C的温度升高会导致肿瘤热疗。这项工作研究了在以大直流磁场B(0)为特征的MRI环境中磁性流体温度的升高情况。使用理论分析和模拟来预测与B(0)垂直的交变正弦和旋转磁场的影响。给出了在适当的磁性流体浓度范围（0.002至0.01固体体积分数）和纳米颗粒半径范围（1至10 nm）内小肿瘤（半径约1 cm）预期温度升高的结果。结果表明，即使在磁性流体饱和度不显著的低场MRI系统中，通过仔细选择旋转或正弦场参数（场频率和幅度），也能发生显著的加热。这项工作表明，将低场MRI与使用超顺磁性氧化铁纳米颗粒的磁热疗系统相结合可能是可行的。
