International Journal on Magnetic Particle Imaging (IJMPI)
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Two-Step Reconstruction with Spatially Adaptive Regularization for Increasing the Dynamic Range in MPI
No full textMagnetic particle imaging is capable of determining very small concentrations of particles if only a single concentration is present in the field-of-view. Meanwhile the determination of particles with widely differing concentrations is still challenging. In a recent work, we introduced a two-step reconstruction method that tackles this problem by isolating the signal of the lower concentrated tracer for a separate reconstruction. In this work, we adapt the two-step reconstruction method in order to apply a joint reconstruction to the entire signal of all particle concentrations. This is achieved by spatially adaptive Tikhonov regularization
In vivo tracking of inhaled nanomagnetosol delivery to the lungs using magnetic particle imaging
No full textNew tools for imaging the lung will aid in the assessment of lung function following infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other lung diseses, and will help guide the development of emerging therapies. Pulmonary drug delivery provides a variety of benefits such as rapid absorption due to the high surgace area of the alveoli, direct air to blood transport, and circumvention of metabolic elimination. To advance new tools for assessing lung function and help develop pummonary delivery methods, we examined the use of aerosolized magnetic nanoparticles (nanomagnetosols) to facilitate magnetic particle imaging (MPI) of the lung. Dextran-coated superparamagnetic iron oxide nanoparticles were fabricated and delivered to the lungs via nebulization in a mouse model. MPI acquired immediately after delivery shows substantial signals in the lungs, which was confrimed by co-registration of X-ray Computed tomographic (CT) images. This study demonstrates that direct delivery of therapeutucs via inhalation can be non-invasively monitored using MPI
MNP Characterization and Signal Prediction using a Model-Based Dictionary
No full textMagnetic Particle Imaging (MPI) utilizes the nonlinear magnetic response of magnetic nanoparticles (MNPs) for signal localization. Accurate modeling of the magnetization behavior of MNPs is crucial for understanding their MPI signal responses. In this work, we propose a model-based dictionary approach using a coupled Brown-Néel rotation model. With experimental results on a Magnetic Particle Spectrometer (MPS), we show that this approach can successfully characterize MNPs and predict their signal responses
Validation of spatial selectivity enhancement for magnetic fluid hyperthermia by introducing ferromagnetic cores
No full textSpatial selectivity plays a crucial role in magnetic fluid hyperthermia because it can define the precision of thermal dose localization and spatial resolution. We propose an application of additional ferromagnetic cores, with high magnetic permeability, to confine the magnetic flux of the selection field coil. An increased gradient leads to increasing spatial selectivity in theranostic therapy of MPI-assisted magnetic fluid hyperthermia. This work validates our recent simulation study [1] by actual experiments of iron core prototypes. This study shows that our core prototypes can increase the gradient by a factor of 1.3 which suggests a 21% improvement in thermal localization in hyperthermia therapy.  
High gradient nested Halbach system for steering magnetic particles
No full textTo transport drugs within the brain to their desired application site it is necessary to overcome the bloodbrain barrier (BBB). To protect the brain from the penetration of harmful substances, the BBB forms anendogenous protection. Different approaches exist to overcome the BBB. One possible approach are magnetic nanoparticles which can be used to move drugs through the blood-brain barrier using magnetic guidance. The system described here consists of three rings of permanent magnets in Halbach configuration with an inner diameter of 5.5 cm, which generate a high gradient of 5.8 T/m at the center, which can be used to study and optimize magnetic transport systems on cell models of a BBB
Immobilized nanoparticles with uniaxial anisotropy in multi-dimensional Lissajous-type excitation: An equilibrium model approach
No full textProper modeling of the magnetization dynamics of the involved magnetic nanoparticles (MNPs) is still one of the open challenges in magnetic particle imaging (MPI) particularly in the multi-dimensional excitation case of Lissajous-type. In this simulation study we focus on the immobilized and oriented MNP case and we investigate similarities and differences between the Fokker-Planck Néel model and an equilibrium model taking into account uniaxial anisotropy
Human-Sized Lightweight Head-Scanner Design
No full textBrain imaging includes various techniques for direct or indirect imaging of the structure or function of the brain. Established clinical imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) require the referral of patients to specialized centres with stationary brain scanners in a shielded environment. However, these restrictions limit the accessibility for many people. For example, it may be difficult to assess time-critical neurological emergencies in a preclinical setting, or to monitor brain function of patients in intensive care units. Here we demonstrate the concept for a wearable brain scanner based on the magnetic particle spectroscopy technology with superparamagnetic iron-oxide nanoparticles (SPIONs) as contrast agent
A closed form solution of magnetic nanoparticles in Rotating drift spectroscopy
No full textAccurate prediction of experimental results is one of the main goals in scientific research. With higher complexity this relies increasingly on accurate numerical simulations. The inductive detection of magnetic nanoparticles often relies on the nonlinear magnetization response of these particles on externally applied time-varying magnetic fields. However, in some cases a closed analytical solution for special cases can be found and used for calibration as well as testing numerical codes. Furthermore, they allow the systematic study of the system and can be starting points for perturbation theory. In this work an analytical solution for the simplest RDS-experiment for magnetic nanoparticles in solution with full 3D motion is presented and compared to the known case of 2D-confined rotation of the nanoparticles
Rotation Unit for Permanent Magnet Based MPI Devices
No full textFor the utilization of the magnetic field of rotating Halbach cylinders in MPI scanners, a rotation unit is required which houses the used permanent magnets and allows their rotation. The setup proposed here allows the concentric arrangement and individual rotation of four Halbach cylinders, whose purely mechanic agitation allows the movement of the field-free region through the field of view. Based on the requirements for such a rotation system, basic design approaches are presented and compared. Initial strength calculations and further simulations were performed on the resulting constructive concept, which, upon implementation, forms the basis for almost purely mechanical MPI scanners
Flexible Software for Rigorous Simulations of Magnetic Particle Imaging Systems
No full textModeling of Magnetic Particle Imaging (MPI) systems allows for developing and testing novel methods for image reconstruction and simulating various setups without the need of real-life measurement data. Here we describe the the initial development of a C++ simulation software designed to provide more realistic MPI simulation data, by accounting for effects like non-linear gradient fields, non-uniform drive fields, space-dependent coil sensitivity, temperature gradients and particle relaxation, as well as the results of the comparison of the simulated signals against real-life Magnetic Particle Spectroscopy (MPS) measurements. In addition to MPI, the software is also suitable for simulating other applications, e.g. MPS, AC susceptibility and pulsed relaxometry measurements