Biosignal Processing Group, Technische Universität Ilmenau, 98693 Ilmenau, Germany.
Electronic Measurements and Signal Processing Group, Technische Universität Ilmenau, 98693 Ilmenau, Germany.
Sensors (Basel). 2021 Oct 4;21(19):6613. doi: 10.3390/s21196613.
Magnetic nanoparticles have been investigated for microwave imaging over the last decade. The use of functionalized magnetic nanoparticles, which are able to accumulate selectively within tumorous tissue, can increase the diagnostic reliability. This paper deals with the detecting and imaging of magnetic nanoparticles by means of ultra-wideband microwave sensing via pseudo-noise technology. The investigations were based on phantom measurements. In the first experiment, we analyzed the detectability of magnetic nanoparticles depending on the magnetic field intensity of the polarizing magnetic field, as well as the viscosity of the target and the surrounding medium in which the particles were embedded, respectively. The results show a nonlinear behavior of the magnetic nanoparticle response depending on the magnetic field intensity for magnetic nanoparticles diluted in distilled water and for magnetic nanoparticles embedded in a solid medium. Furthermore, the maximum amplitude of the magnetic nanoparticles responses varies for the different surrounding materials of the magnetic nanoparticles. In the second experiment, we investigated the influence of the target position on the three-dimensional imaging of the magnetic nanoparticles in a realistic measurement setup for breast cancer imaging. The results show that the magnetic nanoparticles can be detected successfully. However, the intensity of the particles in the image depends on its position due to the path-dependent attenuation, the inhomogeneous microwave illumination of the breast, and the inhomogeneity of the magnetic field. Regarding the last point, we present an approach to compensate for the inhomogeneity of the magnetic field by computing a position-dependent correction factor based on the measured magnetic field intensity and the magnetic susceptibility of the magnetic particles. Moreover, the results indicate an influence of the polarizing magnetic field on the measured ultra-wideband signals even without magnetic nanoparticles. Such a disturbing influence of the polarizing magnetic field on the measurements should be reduced for a robust magnetic nanoparticles detection. Therefore, we analyzed the two-state (ON/OFF) and the sinusoidal modulation of the external magnetic field concerning the detectability of the magnetic nanoparticles with respect to these spurious effects, as well as their practical application.
在过去的十年中，人们一直在研究磁性纳米粒子用于微波成像。使用能够选择性地在肿瘤组织中积累的功能化磁性纳米粒子，可以提高诊断的可靠性。本文涉及通过超宽带微波感应和伪噪声技术检测和成像磁性纳米粒子。这些研究基于幻影测量。在第一个实验中，我们分析了磁性纳米粒子的检测能力，分别取决于极化磁场的磁场强度、目标的粘度以及颗粒所处的周围介质。结果表明，对于稀释在蒸馏水中的磁性纳米粒子和嵌入固体介质中的磁性纳米粒子，磁性纳米粒子的响应随磁场强度呈现非线性行为。此外，磁性纳米粒子的最大响应幅度因周围不同的磁性纳米粒子材料而有所不同。在第二个实验中，我们研究了目标位置对乳腺癌成像实际测量设置中磁性纳米粒子三维成像的影响。结果表明，磁性纳米粒子可以成功检测到。然而，由于路径依赖衰减、乳房不均匀的微波照射以及磁场的不均匀性，图像中颗粒的强度取决于其位置。关于最后一点，我们提出了一种方法，通过基于测量的磁场强度和磁性粒子的磁化率计算位置相关的校正因子来补偿磁场的不均匀性。此外，结果表明，即使没有磁性纳米粒子，极化磁场也会对测量的超宽带信号产生干扰。为了实现稳健的磁性纳米粒子检测，应减少极化磁场对测量的这种干扰影响。因此，我们分析了外部磁场的两种状态（开/关）和正弦调制对磁性纳米粒子的检测能力以及它们的实际应用的影响。
