Dhavalikar Rohan, Rinaldi Carlos
Department of Chemical Engineering, University of Florida, 1030 Center Drive, Gainesville, FL 32611, USA.
J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida,1275 Center Drive, Gainesville, FL 32611, USA.
J Magn Magn Mater. 2016 Dec 1;419:267-273. doi: 10.1016/j.jmmm.2016.06.038. Epub 2016 Jun 16.
Magnetic nanoparticles in alternating magnetic fields (AMFs) transfer some of the field's energy to their surroundings in the form of heat, a property that has attracted significant attention for use in cancer treatment through hyperthermia and in developing magnetic drug carriers that can be actuated to release their cargo externally using magnetic fields. To date, most work in this field has focused on the use of AMFs that actuate heat release by nanoparticles over large regions, without the ability to select specific nanoparticle-loaded regions for heating while leaving other nanoparticle-loaded regions unaffected. In parallel, magnetic particle imaging (MPI) has emerged as a promising approach to image the distribution of magnetic nanoparticle tracers , with sub-millimeter spatial resolution. The underlying principle in MPI is the application of a selection magnetic field gradient, which defines a small region of low bias field, superimposed with an AMF (of lower frequency and amplitude than those normally used to actuate heating by the nanoparticles) to obtain a signal which is proportional to the concentration of particles in the region of low bias field. Here we extend previous models for estimating the energy dissipation rates of magnetic nanoparticles in uniform AMFs to provide theoretical predictions of how the selection magnetic field gradient used in MPI can be used to selectively actuate heating by magnetic nanoparticles in the low bias field region of the selection magnetic field gradient. Theoretical predictions are given for the spatial decay in energy dissipation rate under magnetic field gradients representative of those that can be achieved with current MPI technology. These results underscore the potential of combining MPI and higher amplitude/frequency actuation AMFs to achieve selective magnetic fluid hyperthermia (MFH) guided by MPI.
处于交变磁场（AMF）中的磁性纳米颗粒会以热的形式将部分磁场能量传递给周围环境，这一特性在通过热疗进行癌症治疗以及开发可利用磁场外部驱动释放所载药物的磁性药物载体方面引起了广泛关注。迄今为止，该领域的大多数工作都集中在利用交变磁场促使纳米颗粒在大面积区域释放热量，而无法选择特定的载有纳米颗粒的区域进行加热，同时使其他载有纳米颗粒的区域不受影响。与此同时，磁性粒子成像（MPI）已成为一种有前景的成像磁性纳米颗粒示踪剂分布的方法，其空间分辨率可达亚毫米级。MPI的基本原理是应用一个选择磁场梯度，该梯度定义了一个低偏置场的小区域，再叠加一个交变磁场（其频率和幅度低于通常用于促使纳米颗粒发热的交变磁场），以获得一个与低偏置场区域内颗粒浓度成正比的信号。在此，我们扩展了先前用于估计均匀交变磁场中磁性纳米颗粒能量耗散率的模型，以提供理论预测，说明如何利用MPI中使用的选择磁场梯度来选择性地促使磁性纳米颗粒在选择磁场梯度的低偏置场区域发热。针对代表当前MPI技术所能实现的磁场梯度下能量耗散率的空间衰减给出了理论预测。这些结果强调了结合MPI和更高幅度/频率驱动的交变磁场以实现由MPI引导的选择性磁流体热疗（MFH）的潜力。
