International Journal on Magnetic Particle Imaging (IJMPI)
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OGF-based high-throughput spatial encoding for magnetic particle imaging
No full textEnhancing the signal-to-noise ratio (SNR) is crucial for comprehensively improving the performance of MPI, as it can directly enhance detection sensitivity and indirectly improve spatial resolution due to the increase in the number of available harmonics. However, the strong gradient field in the existing MPI system inevitably leads to the loss of SNR. To deal with this problem, we introduce an oscillating gradient field (OGF) to achieve a high-throughput spatial encoding to improve the SNR of MPI. The time-varying gradient strength allows particle signals from both high and low gradient fields to be captured simultaneously over the sampling period. Preliminary simulation results show that the proposed spatial encoding scheme can generate unique intermodulation signals for particles at each position. And compared with static gradient field with the same peak gradient level, OGF can theoretically generate particle signals with higher SNR
Helical scanning 3D magnetic particle imaging technology
No full textMagnetic particle imaging (MPI) is a novel emerging tomographic technique with high resolution and high sensitivity. Typically, the magnetic fields of MPI scanners are generated by current-carrying coils, resulting in an immense power consumption and making it difficult to apply in clinical research. Halbach array-based MPI devices offer a new solution that greatly reduces device power consumption while providing high gradients. In this work, a mechanically-driven scanning MPI technique was designed using Halbach arrays. This design enables the device to achieve an imaging field of view(FOV) with a diameter of 45 mm, a simulated imaging resolution better than 0.5 mm, and a power consumption of less than 1.5 kW. The feasibility of the device was analyzed through simulation and image reconstruction. In this design, we used extended PSF and extended FOV after deconvolution reconstruction method, which improves the reconstruction resolution by 2-3 times
Integrated hyperthermia and magnetic particle imaging system for localized drug-release
No full textMagnetic Particle Imaging (MPI) is a fast and sensitive imaging modality, which is well suited as a potential theranostic platform. Especially, a combination of MPI with magnetic hyperthermia heating is an appealing strategy. Here, we aim for a spatially focused and controlled drug release via a temperature-induced burst release mechanism. Compared to hyperthermia for cancer treatment, which typically heats the malicious tissue for apoptosis, triggering drug release requires equally high heating power but with minimal duty cycle, i.e. pulsed heating. We generate sufficient heat around the magnetic nanoparticles to trigger release but without excess heating of the surrounding medium or tissue. MNP-local heating requires fast and precise temperature monitoring and feedback to meet the designated release temperature. Our new integrated system reuses the drive field from MPI for simultaneous magnetic heating and spatial imaging to enable monitoring and treatment. Building on previous work [1-3], we first designed a magnetic particle spectroscopy (MPS) device for initial heating experiments. It operates with a) a fiberoptic temperature probe to obtain SAR/SLP values from calorimetric measurements and b) temperature measurements directly from the MNP magnetization signal, allowing cross-validation of both temperature measurement techniques. It also enables fast direct feedback from the magnetically obtained temperature signal to achieve feedback control in MPS and to target the release temperature of the modified MNPs. We have now successfully implemented ac heating and imaging into a fully integrated prototype MPI system (Fig. 1), which will allow temperature monitoring and control for drug release studies on mice shortly
Theranostics based on MPI for brain interventions: an in vivo pilot study
No full textMagnetic particle imaging (MPI)- based magnetic fluid hyperthermia (MFH) enables localized and non-invasive application in conjunction with image guided therapeutic control which represents a significant advantage to established methods of curative heat delivery. Although phantom experiments have shown promising results with adequate MFH performance, transition into clinical and pre-clinical practice, face several challenges. First and foremost, non-invasive, i.e., systemic administration of nanoparticle tracers, results in steadily moving MFH targets that transport the generated heat away from the targetted region. In this pilot study we investigate localized MFH efficiency in the rat brain, during systemic administration of commercial superparamagnetic iron oxide nanoparticles (SPION). For that we used an experimental set up consisting of a custom heating insert integrated into a commercial MPI-scanner. We observed a slight local temperature increase (~0.3-0.5 K) in the brain following simoultanous SPION administration and localized MFH application
Magnetic particle imaging with non-oriented immobilized particles: Why the Langevin model of paramagnetism is sufficient
No full textThe Langevin model of paramagnetism is commonly used as a simplified physical model for magnetic particle imaging. In research with immobilized nanoparticles that are non-oriented, the phenomenon is observed that the measured system function components for Lissajous trajectory-based excitation show a high spatial similarity to those from the Langevin model of paramagnetism. In this work we show that this observation can be explained mathematically, since in equilibrium and for anisotropic uniaxial nanoparticles without orientation the model falls back to the Langevin model of paramagnetism. Since previous studies have also shown that the anisotropic equilibrium model for immobilized particles is approximately equivalent to the Néel rotation Fokker-Planck model, the Langevin model of paramagnetism is sufficient to cover the non-oriented immobilized case
Introducing SMART RHESINs: a novel tracer design for future quantitative magnetic particle imaging (MPI)
No full textMagnetic particle imaging (MPI) is a promising modality in medical imaging leveraging magnetic properties of nanoparticles [1]. So far, mainly commercially available or core/shell nanoparticles have been used [2], but the development of specific MPI tracers promises a better signal detection and opens up new possibilities in biomedicine. In our study, we introduce SMART RHESINs, an innovative tracer architecture specifically designed for MPI [3]. In SMART RHESINs, superparamagnetic nanoparticles (MNPs) with a size of ca. 8 nm are encapsulated in hollow polymer nanospheres with sizes from 150-300 nm. This encapsulation shields MNPs from external factors, ensuring viscosity-independent relaxation of magnetic moment vectors, enabling reliable signal quantification irrespective of the surrounding medium. These tracers not only exhibit superparamagnetic properties, but are also luminescent and do not adversely affect cell viability. The surface of these nanoparticles incorporates functional groups facilitating further customization for e.g., targeted applications. SMART RHESINs are therefore ideal as bimodal imaging tracers for e.g., cancer diagnosis and treatment. Our findings suggest that SMART RHESINs can significantly broaden the application of Magnetic Particle Spectroscopy (MPS) and MPI, offering a modular tracer platform with implications for various physical and biomedical scenarios. This MPI-novel nanoparticle design contributes to the advancement of quantitative MPI techniques
In Vitro Detection of Gastrointestinal Bleeding using Single- and Multi-Contrast MPI
No full textGastrointestinal (GI) bleeding is a potentially life-threatening condition that is typically diagnosed using radiation based imaging modalities such as computed tomography (CT) or catheter-based angiography. Magnetic Particle Imaging (MPI) could provide non-invasive, real-time volumetric imaging without ionizing radiation in future human-sized scanners that covers the entire GI tract. We have developed a human-sized (3D printed) phantom that represents both the bowel lumen and the vascular compartment of the bowel wall. One version has a perforation between the two compartments and a control phantom does not. For single contrast MPI, we evaluate the fluid exchange between the two lumen by observing an administered blood pool tracer. For multi-contrast MPI, the intestinal lumen was filled with an intestinal tracer, which represents an orally administered tracer, to allow co-registration of both tracers at the same location. Both single- and multi-contrast MPI are feasible to visualize GI bleeding and MPI may prove to be a useful tool for radiation-free detection of bleeding throughout the GI tract
Towards machine learning based prediction of magnetic nanoparticle properties
No full textMagnetic nanoparticles (MNP) must fulfill specific requirements according to their dedicated application, e.g. as contrast agents for magnetic particle imaging (MPI) or as heating agents in magnetic fluid hyperthermia (MFH). The synthesis of MNP with specific properties is, however, a complex process, which is not fully understood. Based on standardized parameter studies performed with automated MNP manufacturing techniques, Support Vector Regression (SVR) was used to predict the MNP properties and combine them with the relevant synthesis parameters.
An SVR model with 24 input parameters, i.e. all parameters of the synthesis setup, was used to predict a target property, here the MNP size. For training, the data was split 80?/?20 into training and test set. An extensive grid search for the SVR parameters C, ?, ? and the kernel was conducted using Leave-One-Out cross validation.
The predictive model shows accurate predictions of the desired target property (here the MNP size) with a variance of ±30 nm when predicting the test set. In addition, the predictive model is interpretable and allows to analyze correlations between individual input parameters and the target property. For specific diameters, the MPI signal was determined and will be included in the predictive model in the future.
To conclude, the proposed SVR method yields promising predictions of key MNP characteristics. This method is versatile and can be applied to any synthesis procedure and parameter spectrum making the prediction of the MNP properties possible for specified production process parameters and paving the way for autonomous tailored MNP synthesis
Simulation of a Hand-held Magnetic Particle Imaging Device Utilizing Triangular Waveform Scanning
No full textMagnetic particle imaging (MPI) is an emerging molecular imaging technique, and one of the focus of current research is the imaging devices for human applications. Both closed and open systems face limitations in terms of spatial and power constraints, affecting the detection of large volume. Hand-held MPI device is the representative of low power consumption in MPI devices. It can provide flexibility in human imaging due to the compact size. Current hand-held device consist of signal detection component and mechanical movement component, lacking a gradient field within the device itself. This limitation significantly impacts the resolution and scanning time of hand-held device. Here, we present the design of a novel hand-held device that simulates the generation and movement of Field Free Point (FFP). It can scan a 20 mm*20 mm area at a depth of 8 mm without the movement. Furthermore, due to the small impedance of coils, triangular wave scanning can be employed to enhance trajectory uniformity during the process
Towards sensitive Magnetic Particle Spectroscopy-based immunoassays with adjustable DC offset fields
No full textThe field of homogenous magnetic immunoassays (MIAs) using magnetic nanoparticles (MNPs) as markers has been intensively studied over the past few years. The specific and sensitive measurement of their binding state is of great interest as it can be an alternative to the commonly used methods like rapid antigen tests or PCR. Several methods using various forms of Magnetic Particle Spectroscopy (MPS) are reported in literature. A common approach to achieve higher sensitivities in MPS is to use an additional magnetic DC offset field providing even harmonics or steep phase changes. However, the potential of the additional degree of freedom given by an adjustable DC offset field (ADOF) in particular is often overlooked.Here, we present the advantages of an ADOF to find more sensitive harmonic ratios as a concentration independent metric for the binding status. In order to get a better overview of the DC field dependence for different hydrodynamic sizes, Fokker-Planck simulations for Brownian relaxation were carried out. Subsequently, the successor to our cost-effective immunoMPS with an ADOF was built, focusing on a spectrally pure magnetic excitation field and the decoupling between AC and DC paths. Initial measurements were performed on MNPs in different viscous media and compared to the simulation showing good agreement. In the next step, we are going to synthesize and measure different MNP clusters sizes before we move on to test this principle on real biological targets