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Magnetic Particle Imaging (MPI) is a fast imaging technique for the visualization of the distribution of superparamagnetic iron-oxide nanoparticles (SPIONs) in 3D. For spatial encoding, a field free area is moved rapidly through the field of view (FOV) generating a localized signal. Fast moving samples, e.g., a bolus of SPIONs traveling through the large veins in the human body carried by blood flow with velocities in the order of ~45 cm/s and higher, cause temporal blurring in MPI measurements using common sequences and reconstruction techniques. This hampers the evaluation of dynamics of rapidly moving samples. In this abstract, initial results of rapidly moving samples in form of SPION boluses visualized within an MPI scanner are shown., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Critical Offset Magnetic PArticle SpectroScopy (COMPASS) is a new method that allows to detect slight changes in the mobility of particles in a solution very sensitively. While first applications in detecting biomarkers such as SARS CoV 2 antibodies show very promising results, the full potential of the technique and the underlying physical effects were yet only considered superficially. Here we present the first results of a detailed study of the behavior of the particle signal under variations of relevant system parameters with a focus on particle size, viscosity and temperature of the solution to win more information about the behavior of the effect and find new interesting application possibilities., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Rotational Drift Spectroscopy (RDS) is a novel spectroscopic method for magnetic nanoparticles. It is based on measuring the rotational drift of magnetic nanoparticle ensembles in a rotating magnetic field, which is below the magnetic field strength necessary for rotating the magnetic nanoparticles synchronously. Magnetorelaxometry (MRX) measures the decaying magnetization after applying a magnetic pulse, allowing to determine the zero-field relaxation time of magnetic particle systems. It is used, e.g., for general particle characterization or bioassay applications. The following work presents pulsed RDS sequences for measuring the zero-field relaxation behavior of magnetic particles. Measuring the zero-field relaxation using an RDS setup provides the advantage of allowing the combination of additional measurement sequences for more specific particle characterizations. The pulse sequence can be tailored to the necessary relaxation time range of the particle system, allowing to cover a wide range of different relaxation times., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Phantoms of blood vessels are an important part of flow measurements and should behave as realistic as possible compared to human blood vessels. A step-by-step guide is presented on how to obtain realistic 3D models of blood vessels applicable for 3D printing and simulation studies. The resulting 3D models have realistic dimensions, are waterproof and could be used in a human-sized MPI scanner. The 3D printed phantoms with vascular pathologies like aneurysm or stenosis were used in static and real-time bolus tracking measurements., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

MPI has been on a trajectory towards clinical application in humans for years. As scanners and techniques mature, clinical testing is effectively prohibited by the lack of a clinically approved tracer. This changes now by the reintroduction of a Ferucarbotran-based tracer into the market, Resotran®. Although initially intended for use in MRI, we tested Resotran® for its viability in MPI. The other Ferucarbotran-based tracer fit for MRI and MPI is Resovist®, which is well known and characterized but was discontinued years ago. We present initial data on the characterization of Resotran® in comparison to Resovist®., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Based on a novel open design implementing the so-called traveling wave MPI approach, the open interventional MPI (iMPI) system provides imaging of tracers based on superparamagnetic iron oxide nanoparticles (SPIONs) with high sensitivity, optimal patient handling and would even allow hybrid imaging of magnetic tracers within gold standard x-ray based interventional angiography systems. In initial experiments, the feasibility of a human-sized interventional MPI scanner with real-time data reconstruction and image visualization is demonstrated within a percutaneous transluminal angioplasty (PTA)., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Rotational Drift Spectroscopy (RDS) is a novel spectroscopic method for magnetic nanoparticles. It is based on measuring the rotational drift of magnetic nanoparticle ensembles in liquid suspension in a rotating magnetic field, that is below the magnetic field strength necessary for rotating the magnetic nanoparticles synchronously. The resulting asynchronous rotational drift strongly depends on the properties of the magnetic nanoparticles and their environment. This allows for, e.g., detecting specific molecules via functionalized magnetic nanoparticles. The following work presents a compact rotational drift spectroscopy hardware design, which is controllable with python scripts and is especially designed for accommodating various kinds of RDS measurement sequences with differing hardware requirements., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Endovascular treatment of human aneurysms with stent grafts is an established therapeutic strategy to treat ruptured and unruptured arterial aneurysms. These stents are covered with a membrane that blocks blood flow to the aneurysm and promotes healing of the vessel. To date, digital subtraction angiography (DSA) has been gold standard for image-guided stent graft application. However, DSA is associated with significant disadvantages including its invasiveness, the need for potentially nephrotoxic iodine-based contrast agents and exposure to ionizing radiation for patients and clinical staff. Magnetic particle imaging (MPI) is a fast and sensitive tomographic imaging technique that uses magnetic fields to visualize superparamagnetic iron-oxide nanoparticles (SPIONs). The advantages of MPI include the background- and radiation-free visualization of SPION-tracers. The aim of this proof-of-concept study was to demonstrate the potential of MPI for image-guided application of covered stents in a 3D printed realistic aneurysm phantom., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Current bioassays for detection of antibodies or antigens such as ELISA (Enzyme-linked Immunosorbent Assay) are relatively inflexible, expensive and time-consuming. Upcoming methods, such as ACS (AC susceptometry) or MPS (Magnetic Particle Spectroscopy), exploit the magnetization response of functionalized MNP ensembles to assess specific information about the MNP mobility as well as conjugations of chemical or biological compounds on their surface. Both methods have shown promising results in the past but cannot reach the sensitivity of above-mentioned techniques. We used a novel method based on a modified MPS being sensitive to minimal changes in mobility of MNP ensembles. This facilitates robust and easy-to-handle measurements of minimal changes in the diameter of MNPs. As an example, we detected SARS-CoV-2 antibodies binding to the S1 antigen on the surface of functionalized MNPs. Without any purification or incubation, we could show a sensitivity of less than 50 ng/mL of SARS-CoV-2 antibodies in human blood., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Investigation of influence of metallic endoprostheses on MPI functionality in a human-sized MPI scanner. No relevant impairment of imaging from the presence of endoprosthesis could be found., International Journal on Magnetic Particle Imaging IJMPI, Vol 9 No 1 Suppl 1 (2023)

Magnetic Particle Imaging (MPI) has become a promising candidate for medical applications, especially cardiovascular interventions. Necessary milestones have been reached in multiple pre-clinical experiments and studies and are ready to be tested on human-scale MPI scanners. Only few human-sized scanner systems designed for dedicated applications are available. In this abstract, a novel approach is presented for a dedicated human-sized interventional MPI scanner., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

4D flow experiments, as known from MRI, are useful to examine the fluid dynamics in complex vessel geometries with high accuracy. The transfer to a positive contrasted fast and sensitive modality, such as MPI, offers new insights into dynamic particle flow under real-time visualization. In particular, measurements in 3D printed vascular phantoms are beneficial since they allow studies of the complicated flow-related interrelations causing the development of pathologies and also provide a quality control for the development of more realistic vascular phantoms. The presented framework provides an easy-to-use processing from extraction of desired vessel structures from 3D MRI or CT data over preparation them for 3D printing and further processing to final measurements., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

Magnetic Particle Imaging (MPI) is a novel imaging technique utilizing time-varying magnetic fields to determine the distribution of superparamagnetic iron-oxide nanoparticles in 3D. The usage of electrical coils for the generation of the desired strong magnetic field gradient as well as the time-varying magnetic fields allows flexible and fast imaging, but the corresponding high energy consumption also requires sophisticated cooling. The usage of permanent magnets provides the advantage of generating high magnetic field gradients without requiring electrical power and cooling, but also brings limitations with respect of flexibility and the size of the field of view. A novel approach utilizing rotatable Halbach rings is introduced, which overcomes the restrictions of static permanent magnet designs and provides the flexibility of a mechanically driven Traveling Wave MPI scanner., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

Field-free line (FFL) Magnetic Particle Imaging (MPI) scanners are of high interest for fast and accurate scanning of 3D samples because of the higher signal-to-noise ratio due to the enlarged encoding scheme. Until now, only magnetic field generators have been presented providing an electrical rotation and displacement of an FFL within a 2D slice. Utilizing double-helix coils and the Traveling Wave approach, a full 3D FFL MPI scanner can be introduced, providing fast 3D imaging with less hardware efforts., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

Accurate 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., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

Rotational Drift Spectroscopy (RDS) is a novel spectroscopic method for magnetic nanoparticles. It is based on measuring the rotational drift of magnetic nanoparticle ensembles in a rotating magnetic field, which is below the magnetic field strength necessary for rotating the magnetic nanoparticles synchronously. The resulting asynchronous rotational drift strongly depends on the properties of the magnetic nanoparticles and their environment. This provides a promising basis for spectroscopic measurements with high sensitivity as well as high specificity, e.g., detecting specific molecules in a liquid via functionalized magnetic nanoparticles. In this work, multiparametric Rotational Drift Spectroscopy (mRDS) is presented, which makes use of the nonlinear dependency of the RDS signal of, e.g., the sequence amplitude and the viscosity of the suspending liquid of the magnetic particle sample. This allows access to a variety of parameters of magnetic nanoparticle suspensions., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

The success of tracer-based tomographic methods, such as Magnetic Particle Imaging (MPI), depends on two factors primarily: scanner hardware and tracer performance. Within the last years, several hardware improvements have been presented improving temporal and spatial resolution of MPI systems. However, there was still a lack of efficient commercially available tracers for MPI. Here we report on synomag® particles as a new tracer tailored for MPI, which shows almost four-times higher signal in a Traveling Wave MPI scanner than the established tracer Resovist®. Int. J. Mag. Part. Imag. 7(1), 2021, Article ID: 2103003, DOI: 10.18416/IJMPI.2021.2103003, International Journal on Magnetic Particle Imaging, Vol 7 No 1 (2021)

Magnetic particle imaging (MPI) is a tomographic imaging method to determine the spatial distribution of magnetic nanoparticles (MNP) within a defined volume. To evaluate the spatio-temporal resolution of existing MPI scanners, we developed dynamic MPI measurement phantoms. These segmented flow phantoms consist of a bolus of ferrofluid tracer material, pumped through a tube system. Using a hydrophobic organic carrier oil, cylindrically shaped bolus of different diameter, length, MNP concentrations, and flow velocity can be emulated. Moving boluses were imaged by MPI and the correlation of spatial resolution und velocity of the bolus was investigated. For all bolus dimension and flow velocity combinations, a decreasing spatial resolution and increasing blurring with increasing bolus velocity and decreasing bolus volume was observed. Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009011, DOI: 10.18416/IJMPI.2020.2009011, International Journal on Magnetic Particle Imaging, Vol 6 No 2 Suppl. 1 (2020)

The first issue of the fifth volume of the International Journal on Magnetic Particle Imaging (IJMPI) comes with four manuscripts, covering the topics of instrumentation, particle characterization, image reconstruction and standardization in the field of MPI. The manuscripts describe a novel and sensitive signal detector for magnetic fields, an open-source software package for data processing and reconstruction, a new kind of spectrometer for particle characterization, and a temporal polyrigid registration method for reconstructed MPI patches handling possible motion of large objects during imaging. Int. J. Mag. Part. Imag. 5(1-2), 2020, Article ID: 2003002, DOI: 10.18416/IJMPI.2020.2003002, International Journal on Magnetic Particle Imaging, Vol 5 No 1-2 (2019)