Tomographic temperature imaging with magnetic nanoparticles

物体表面下的无创温度成像是一个热门且具有挑战性的课题。本课题提出了一种实现高空间、温度和时间分辨率层析温度成像的新方法。在梯度直流磁场和均匀交流磁场中，点MNP样品的各奇次谐波幅值随点样品与时间平均场自由点（aFFP）距离的增加而减小，表现为点扩展函数（PSF）形状。因此，视场中MNP集合的每个奇谐波的幅值可以用PSF和由局部MNP产生的相应谐波的卷积来表示。现有的MPI扫描仪进行了修改，以实现aFFP扫描，为MNP激励产生交流磁场，并测量MNP磁化的三次和五次谐波。基于相应的谐波PSF，提出了一种单独的反卷积方法来对3次和5次谐波进行反卷积。因此，利用基于静态朗格万函数的MNP测温技术，利用反卷积的三次和五次谐波实现了温度成像。模拟实验验证了该方法在温度成像中的可行性。然后，分别研究了迭代反褶积和约束条件下的联合反褶积，以改善温度成像。进一步研究了MNP动力学对MNP测温的影响，实现了包含MNP动力学的MNP测温。因此，在高频交流磁场中应用MNP测温技术（包括MNP动力学），通过快速aFFP扫描实现了快速温度成像。我们强调，这个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，并且在诸如磁热疗等生物医学应用以及其他生物和工业任务方面具有前景。

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.