IEEE Trans Med Imaging. 2022 Dec;41(12):3774-3786. doi: 10.1109/TMI.2022.3195694. Epub 2022 Dec 2.
Magnetic particle imaging (MPI) is a rapidly developing medical imaging modality that exploits the non-linear response of magnetic nanoparticles (MNPs). Color MPI widens the functionality of MPI, empowering it with the capability to distinguish different MNPs and/or MNP environments. The system function approach for color MPI relies on extensive calibrations that capture the differences in the harmonic responses of the MNPs. An alternative calibration-free x-space-based method called TAURUS estimates a map of the relaxation time constant, τ , by recovering the underlying mirror symmetry in the MPI signal. However, TAURUS requires a back and forth scanning of a given region, restricting its usage to slow trajectories with constant or piecewise constant focus fields (FFs). In this work, we propose a novel technique to increase the performance of TAURUS and enable τ map estimation for rapid and multi-dimensional trajectories. The proposed technique is based on correcting the distortions on mirror symmetry induced by time-varying FFs. We demonstrate via simulations and experiments in our in-house MPI scanner that the proposed method successfully estimates high-fidelity τ maps for rapid trajectories that provide orders of magnitude reduction in scanning time (over 300 fold for simulations and over 8 fold for experiments) while preserving the calibration-free property of TAURUS.
磁粒子成像（MPI）是一种快速发展的医学成像方式，利用磁性纳米粒子（MNPs）的非线性响应。彩色 MPI 拓宽了 MPI 的功能，使其能够区分不同的 MNPs 和/或 MNP 环境。彩色 MPI 的系统功能方法依赖于广泛的校准，以捕捉 MNPs 的谐波响应差异。一种替代的无校准 x 空间方法称为 TAURUS，通过恢复 MPI 信号中的镜像对称性来估计弛豫时间常数 τ 的图。然而，TAURUS 需要对给定区域进行来回扫描，这限制了其在具有恒定或分段恒定焦点场（FF）的缓慢轨迹中的使用。在这项工作中，我们提出了一种新的技术来提高 TAURUS 的性能，并为快速和多维轨迹实现 τ 图估计。所提出的技术基于校正由时变 FF 引起的镜像对称性的失真。我们通过在我们的内部 MPI 扫描仪中的模拟和实验证明，所提出的方法成功地估计了快速轨迹的高保真 τ 图，与模拟相比，扫描时间减少了几个数量级（超过 300 倍），与实验相比，扫描时间减少了 8 倍），同时保持了 TAURUS 的无校准特性。
