Tomographic temperature imaging with magnetic nanoparticles

物体表面下的无创温度成像是一个热点和具有挑战性的课题。本课题提出了一种实现高空间分辨率、高温度分辨率和高时间分辨率的层析温度成像新方法。在梯度直流磁场和均匀交流磁场中，点MNP样品的各奇次谐波的幅值随点样品与时均场自由点(AFFP)距离的增加而减小，呈点扩展函数(PSF)形状。因此，在视场中组装的MNP的每个奇次谐波的幅度可以用PSF和由局部MNP产生的对应的谐波的卷积来表示。对现有的MPI扫描仪进行了改进，使其能够进行aFFP扫描，产生用于MNP激励的交流磁场，并测量MNP磁化强度的3次和5次谐波。提出了一种基于对应的谐波点扩散函数的三次和五次谐波的单独反卷积方法。在静态朗之万法的基础上，应用MNP测温技术，实现了三次和五次谐波的解卷积温度成像。通过人体模型实验验证了该温度成像方法的可行性。然后，分别研究了迭代反褶积和带约束条件的联合反褶积，以改善温度成像。进一步研究了MNP动力学对MNP测温的影响，以实现包括MNP动力学在内的MNP测温。因此，应用包括MNP动力学的MNP测温技术，通过在高频交流磁场中进行快速aFFP扫描，实现了快速温度成像。我们强调，这一拟议项目的成果在物体表面下的温度成像方面具有巨大的潜力，并有望用于生物医学应用，如磁热疗，但也可用于其他生物和工业任务。

Noninvasive temperature imaging beneath the surface of an object is a hot and challenging topic. This project proposes a new method to realize tomographic temperature imaging with high spatial, temperature and temporal resolutions. In a gradient dc magnetic field and a homogeneous ac magnetic field, the amplitude of each odd harmonic of a spot MNP sample decreases with increasing the distance between the spot sample and a time-average field free point (aFFP), which shows a point spread function (PSF) shape. Thus, the amplitude of each odd harmonic of a MNP assemble in a field of view can be expressed by the convolution of the PSF and the corresponding harmonic generated by the local MNPs. An existing MPI scanner is modified to enable the aFFP scanning, the generation of an ac magnetic field for MNP excitation and the measurements of the 3rd and 5th harmonics of MNP magnetization. A separate deconvolution is proposed to deconvolute the 3rd and 5th harmonics based on the corresponding harmonic PSF. Consequently, temperature imaging is realized with the deconvoluted 3rd and 5th harmonics applying MNP thermometry based on the static Langevin function. Phantom experiments are performed to demonstrate the feasibility of the proposed method for temperature imaging. Afterwards, an iterative deconvolution and a joint deconvolution with constrained conditions are, respectively, investigated to improve the temperature imaging. Furthermore, the influence of MNP dynamics on MNP thermometry is investigated to realize MNP thermometry including MNP dynamics. Consequently, a fast temperature imaging is realized with a fast aFFP scanning in a high-frequency ac magnetic field applying MNP thermometry including MNP dynamics. We emphasize that the outcomes of this proposed project have great potential for the temperature imaging beneath the surface of an object and are promising for biomedical applications such as magnetic hyperthermia, but also for other biological and industrial tasks.