Development of a novel MPI scanner based on a field free line

本项目的目的是设计、实现和研究一种具有创新拓扑结构的实时磁粒子成像（MPI）扫描仪，其中首次使用旋转永磁体进行施工。最重要的是最小化功率损耗和可实现的视场尺寸。临床成功的层析成像设备的基本标准是高空间分辨率，高灵敏度，实时能力和对患者的风险最小。考虑到这些标准的组合，磁颗粒成像（MPI）正在制定新的标准。这种模式是基于纳米颗粒的可视化，其核心由超顺磁性氧化铁（SPIO）组成。spio最重要的物理特性是非线性磁化曲线和饱和特性。当受到正弦振荡磁场（驱动场）时，粒子磁化的非线性使粒子发出非正弦电磁信号，从而产生信号。然后可以测量该信号的高次谐波。一个附加的磁梯度场（选择场）用于空间编码。这个磁场产生的方式是，在产生的磁通量密度消失（FFP：无场点）的一个不同点之外的所有粒子都处于磁饱和状态。这样，空间编码就实现了，因为只有FFP内部的粒子才会产生信号。用无场线（FFL）代替FFP可以大大提高该技术的灵敏度。当FFL在视场上缓慢旋转和快速移动时，获得了足够的信息，用于类似ct的粒子分布空间重建。到目前为止，由于产生电磁线圈的选择场的高功率损耗，在世界范围内实现具有实时功能的ffl扫描仪失败了。该研究项目的重点是开发第一台动态FFL扫描仪，该扫描仪使用永磁体产生FFL选择场。对于磁体的几何形状，将采用创新的扫描仪拓扑结构。线圈数量的减少将减少单个信号路径的耦合，这通常会导致磁场质量的降低和非常高的能量需求。此外，不需要线圈、电源和模拟滤波器来产生选择场。然而，主要的优点将是将功率损耗降低到具有电磁选择场线圈的类似扫描仪的0.1%以下。此外，由于FFL的机械旋转，可以分析选择场的时间依赖性对成像过程的影响。

The purposes of the presented project are the design, realization, and investigation of a real-time capable Magnetic Particle Imaging (MPI) scanner with an innovative topology, where for the first time rotating permanent magnets are used for construction. Of great relevance are the minimized power loss and the achievable size of the field of view. Essential criteria for a clinically successful tomographic imaging device are a high spatial resolution, a high sensitivity, the real-time capability and a minimal risk for the patient. Considering a combination of these criteria, Magnetic Particle Imaging (MPI) is setting new standards. The modality is based on the visualization of nanoparticles with a core that consists of super-paramagnetic iron oxide (SPIO).The most important physical characteristics of the SPIOs are the non-linear magnetization curve and the saturation behavior. The non-linearity of the particle magnetization enables signal generation, by causing the particles to emit a non-sinusoidal electromagnetic signal, when subjected to a sinusoidally oscillating magnetic field (drive field). The higher harmonics of this signal can then be measured. An additional magnetic gradient field (selection field) is used for spatial encoding. This field is generated in a way that all particles outside a distinct point, where the resulting magnetic flux density vanishes (FFP: field-free point), are in magnetic saturation. This way, spatial encoding is achieved, since only particles inside the FFP generate a signal.The sensitivity of the technique can be greatly improved by using a field-free line (FFL) instead of an FFP. Sufficient information for a CT-like spatial reconstruction of the particle distribution is acquired, when the FFL is slowly rotated and quickly shifted over the field of view.So far, the realization of real-time capable FFL-scanners failed worldwide, due to the high power losses in the selection field generating electromagnetic coils. The key point for the proposed research project is the development of the first dynamical FFL scanner that generates the FFL-selection-field with permanent magnets. For the geometry of the magnets an innovative scanner topology will be utilized.The reduction of the number of coils will reduce the coupling of the individual signal paths, which typically leads to a reduction of the magnetic field quality and to a very high energy demand. Additionally, no coils, power sources and analogue filters are needed for the generation of the selection field. However, the main advantage will be the reduction of power losses to below 0.1 % of a comparable scanner with electromagnetic selection field coils. Additionally, due to the mechanical FFL rotation, the influence of the time dependency of the selection field on the imaging process can be analyzed.