UMIT TIROL - Private University for Health Sciences and Health Technology, A-6060 Hall in Tirol, Austria.
Physikalisch-Technische Bundesanstalt (PTB), D-10587 Berlin and dD38116 Braunschweig, Germany.
Phys Med Biol. 2023 Jul 19;68(15). doi: 10.1088/1361-6560/ace304.
Magnetorelaxomety imaging (MRXI) is a noninvasive imaging technique for quantitative detection of magnetic nanoparticles (MNPs). The qualitative and quantitative knowledge of the MNP distribution inside the body is a prerequisite for a number of arising biomedical applications, such as magnetic drug targeting and magnetic hyperthermia therapy. It was shown throughout numerous studies that MRXI is able to successfully localize and quantify MNP ensembles in volumes up to the size of a human head. However, deeper regions that lie far from the excitation coils and the magnetic sensors are harder to reconstruct due to the weaker signals from the MNPs in these areas. On the one hand, stronger magnetic fields need to be applied to produce measurable signals from such MNP distributions to further upscale MRXI, on the other hand, this invalidates the assumption of a linear relation between applied magnetic field and particle magnetization in the current MRXI forward model which is required for the imaging procedure.We tackle this problem by introducing a nonlinear MRXI forward model that is also valid for strong magnetic excitation fields.We demonstrate in our experimental feasibility study that scaling up the imaging region to the size of a human torso using nonlinear MRXI is possible. Despite the extreme simplicity of the imaging setup applied in this study, an immobilized MNP sample with 6.3 cmand 12 mg Fe could be localized and quantified with an acceptable quality.A well-engineered MRXI setup could provide much better imaging qualities in shorter data acquisition times, making nonlinear MRXI a viable option for the supervision of MNP related therapies in all regions of the human body, specifically magnetic hyperthermia.
磁共振弛豫成像（MRXI）是一种用于定量检测磁性纳米粒子（MNPs）的非侵入性成像技术。对体内 MNPs 分布的定性和定量了解是许多新兴生物医学应用的前提，例如磁性药物靶向和磁热疗。大量研究表明，MRXI 能够成功地在高达人头大小的体积内定位和定量 MNPs 集合。然而，由于这些区域中的 MNPs 的信号较弱，因此很难重建更远的、远离激励线圈和磁传感器的更深区域。一方面，需要施加更强的磁场才能从这些 MNP 分布中产生可测量的信号，以进一步扩展 MRXI；另一方面，这会使当前 MRXI 正向模型中应用磁场与粒子磁化之间的线性关系的假设无效，而这是成像过程所必需的。我们通过引入一个也适用于强磁场激励的非线性 MRXI 正向模型来解决这个问题。我们在实验可行性研究中证明，使用非线性 MRXI 将成像区域扩展到人 torso 的大小是可行的。尽管在这项研究中应用的成像设置极其简单，但仍可以对一个固定的、具有 6.3cm 和 12mg Fe 的 MNPs 样本进行定位和定量，且质量可接受。一个设计良好的 MRXI 设备可以在更短的数据采集时间内提供更好的成像质量，这使得非线性 MRXI 成为在人体所有区域（特别是磁热疗）监测 MNP 相关治疗的可行选择。
