International Journal on Magnetic Particle Imaging IJMPI
The International Journal on Magnetic Particle Imaging IJMPI encourages the submission of manuscripts in all research fields related to Magnetic Particle Imaging MPI. www.iwmpi.org
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Low-Frequency Gradiometers for Closed-Loop Control of Magnetic Microrobots
Because they can readily generate gradients and time-varying fields, magnetic particle imaging (MPI) apparatuses are increasingly considered for the dual purpose of manipulating and sensing biomedical magnetic microrobots. Feedback about the position and orientation of microrobots is an essential requirement for closed-loop control, and reading out this information magnetically is especially desirable for physiological targets. A typical approach is to toggle between a low frequency (<100 Hz) actuation mode, where field gradients or low frequency rotating fields act to propel microrobots, and a sensing mode based on MPI in the 10s of kHz for detecting their position and posture. Although making use of sequential actuation and sensing leverages established techniques from MPI, an ideal approach would offer uninterrupted actuation and sensing. We have previously demonstrated the possibility of simultaneously actuating and inductively sensing at frequencies in the Hz or 10s of Hz. Here, we extend these concepts by showing how low-frequency gradiometers can be designed to sense position and torque delivery to microrobots. As an illustrative example, we demonstrate a prototype apparatus that controls a helical swimming magnetic robot with inductive feedback. We further demonstrate how gradiometers can be designed as add-ons to commercial magnetic field generators and how they can be adapted for setups based on rotating permanent magnets. These efforts advance toward instrumentation for simultaneous inductive sensing at frequencies <100 Hz that can be incorporated into magnetic actuation apparatuses.
Copyright (c) 2026 Tim Grossrieder, Cameron Forbrigger, Myungjin Park, Michael Christiansen, Simone Schuerle https://creativecommons.org/licenses/by/4.0
Coagulation Induced MPS-Signal Changes in Human Blood Samples
With the clinical approval of the MRI contrast agent Resotran and the development of first human-scale Magnetic Particle Imaging (MPI) scanners, clinical applications of MPI are within reach. Magnetic Particle Spectroscopy (MPS), the non-imaging counterpart of MPI, allows for highly sensitive analysis by utilizing the signal responses of magnetic nanoparticles. The use of MPS as point-of-care (PoC) devices and -applications is very advantageous. In this study, we evaluate the potential of MPS to monitor blood coagulation in real time.
Copyright (c) 2026 Maria-Josephina Buhné, Justin Ackers, Mandy Ahlborg , Matthias Graeser, Throsten Buzug , Kerstin Lüdtke-Buzug , Tobias Knopp, Jonas Stroeder , Jörg Barkhausen, Roman Kloeckner, Alex Frydrychowicz, Franz Wegner, Eric Aderhold https://creativecommons.org/licenses/by/4.0
Real-time detection of single magnetic nanoparticle with interferometric scattering microscopy
Magnetic nanoparticles (MNPs) have extensive applications in multimodal imaging, drug delivery and cell therapy techniques due to the magnetic and chemical properties. However, existing methods only can detect the signal of hundreds of MNPs, hindering insights into their dynamic behaviors in microscopic scale. In this study, we propose an interferometric scattering (iSCAT) microscopy based method to track the motion of single MNP in the pure water. In our method, we induce directional displacement of MNPs with applying a magnetic field gradient. Experimental results show that the motion of MNPs is consistently aligned with the magnetic field direction, validating the feasibility of the proposed method. The proposed method provides a promising approach to reveal the microscopic behaviour of MNPs.
Copyright (c) 2026 Wenzhong Liu, Yi Ding, Yulong Dong https://creativecommons.org/licenses/by/4.0
Performance evaluation of different surface receiving coils using single-sided magnetic particle spectrometer
Magnetic particle imaging (MPI) is an emerging molecular imaging technique characterized by high sensitivity and high resolution. The single-sided MPI system, owing to its compact size and high portability, is well-suited for clinical use. However, it faces challenges in detection depth and sensitivity, and relies heavily on receiver coils. This study investigates the impact of different surface receiver coil topologies on the performance of single-sided magnetic particle spectrometers under strict constraints of fixed wire length. Through electro-magnetic simulation and characterization of ring-shape, solenoid, raceway, single-D, double-D, and gradient annular coils, the results reveals that distinct performance trade-offs emerge across different topologies. Ring-shaped, track-shaped, and single D-shaped coils demonstrate superior surface sensitivity, while solenoid coils excel in providing a large-area magnetic response zone within the coil. Further analysis reveals that double-D coils can achieve two distinct spatial sensitivity distributions (elliptical wide-field or figure-eight gradient fields) depending on the connection mode. This dual capability of double-D coils holds potential for biomedical applications like highly sensitive tumor screening and precise localization.
Copyright (c) 2026 Runze Li, Yidong Liao, Zechen Wei, Jie Tian, Hui Hui https://creativecommons.org/licenses/by/4.0
Human Head Exposure to Multidimensional Magnetic Fields in MPI: A Simulation-Based Safety Study
The translation of magnetic particle imaging (MPI) scanners into a clinical stage requires a detailed risk and safety assessment. In order to perform human experiments, the influence of the magnetic fields in use onto the human body have to be evaluated, in particular with view on peripheral nerve stimulation (PNS). While multidimensional excitation studies have been conducted with human abdomen, PNS studies of the human head were limited to a single excitation axis up to this date. In this work, we simulate the expected induced current density of our two-axis MPI scanner drive fields when applied to a detailed anatomical human head model. We compare the acquired results with the defined basic restrictions of the International Commission on Non-Ionizing Radiation Protection and discuss the consequences.
Copyright (c) 2026 Jonas Faltinath, Fynn Foerger, Florian Thieben, Tobias Knopp https://creativecommons.org/licenses/by/4.0
A Single-Harmonic Amplitude-Phase Cross-Point Method for Estimating Hydrodynamic Diameter of Magnetic Nanoparticles
The precise and rapid measurement of the hydrodynamic diameter of magnetic nanoparticles (MNPs) is crucial for their synthesis and biomedical applications. This paper introduces a novel measurement metric, the Decline Cross-Point (DCP), derived from the amplitude and phase curves of a single harmonic in Field-Swept Magnetic Particle Spectroscopy (FS-MPS), for rapid estimation of the MNP hydrodynamic diameter. Unlike conventional methods that rely solely on harmonic amplitude, the incorporation of phase information significantly enhances the measurement sensitivity. Simulation results based on the Fokker-Planck equation established a strong linear correlation between the DCP and the hydrodynamic diameter. Experimental validations were conducted using three commercial MNP tracers (Synomag-D: 50 nm, Vivotrax: 62 nm, Perimag: 130 nm) on a custom FS-MPS system. The results demonstrate a highly linear relationship between the measured DCP and the manufacturer-specified hydrodynamic diameters. The proposed DCP method offers a sensitive, rapid, and cost-effective solution for in-situ monitoring of MNP size during synthesis and for characterizing functionalized MNPs in bioassays.
Copyright (c) 2026 Yidong Liao, Hui Hui, Jie Tian https://creativecommons.org/licenses/by/4.0
Investigating and calibration methods on signal quantification for Magnetic Particle Imaging (MPI)
Magnetic Particle Imaging (MPI) is an emerging imaging modality that enables the quantitative and real-time visualization of superparamagnetic iron oxide nanoparticles (SPIONs). Its unique ability to directly detect and quantify SPION concentrations in vivo has positioned MPI as a promising tool for various biomedical applications, including cancer detection, targeted drug delivery, and cell tracking.1,2 However, achieving accurate and reproducible quantification requires standardized calibration approaches that account for differences in SPION properties and experimental conditions.3-5 Herin we examine systematic differences in signal quantification of two calibration methods employing two commercially available tracers employed in MPI: ProMag and VivoTrax. The methods were: a fixed-volume approach, commonly used in biological studies for dilution series and calibration curves; and a fixed-concentration approach, which maintains a constant SPION concentration while increasing total iron content. Analysis revealed significant differences in signal quantification between the two calibration methods, with more pronounced discrepancies observed as dilution increased. These differences were likely due to reduced SPION-SPION interactions at lower concentrations, leading to reduced signal strength and broader (lower resolution) images. These findings highlight the potential advantages of the fixed-concentration method, which helps preserve SPION-SPION interactions and may offer improved accuracy, particularly when maintaining stable nanoparticle interactions is crucial. This study highlights the importance of SPION properties, environmental interactions, and calibration methods in MPI signal quantification. Differences in SPION behaviour, especially at varying concentrations, affect the MPI signal. By comparing calibration methods, this work aims to standardize MPI protocols, ensuring more accurate results in solution-based experiments and providing a foundation for future cell-based studies. The findings enhance understanding of MPI signal behaviour under various calibration methods, enabling more precise SPION quantification.
Copyright (c) 2026 Marco Giardiello https://creativecommons.org/licenses/by/4.0
A symmetric receive coil design for sentinel lymph node imaging
Magnetic Particle Imaging (MPI) based sentinel lymph node detection provides a novel technical approach for investigating lymphatic metastasis and therapeutic response in tumors. However, current MPI systems mainly employ global receive coils, which exhibit limited spatial specificity and low local sensitivity. In this study, a dedicated positioning platform and a symmetric surface receive coil were designed for localized MPI of the inguinal lymph node in mouse applications, enabling stable animal fixation and precise anatomical alignment. Experimental results demonstrated that the proposed design achieved high local sensitivity for magnetic particle signal detection.
Copyright (c) 2026 Haicheng Du, Guanghui Li, Ziwei Chen, Jie Tian, Yu An https://creativecommons.org/licenses/by/4.0
Normalized Quantitative Assessment of Receive-Coil Sensitivity using MPI Transfer Function Measurements
In human-scale magnetic particle imaging (MPI), field inhomogeneities arise because a large fraction of the bore volume is utilized for imaging. Accurate knowledge of the receive-coil sensitivity is essential for hybrid system-matrix generation and model-based system matrix reconstruction. In this work, we present an efficient approach for measuring normalized receive-field profiles using a calibration coil and a small number of measurements.
Copyright (c) 2026 Florian Thieben, Egor Kretov, Onurcan Topcu, Haozhe Wang, Takashi Yoshida, Matthias Graeser, Mandy Ahlborg, Tobias Knopp https://creativecommons.org/licenses/by/4.0
Investigation of impact of tuning coil loading on particle signal harmonics in multi-frequency MPI
In Magnetic Particle Imaging (MPI), suppression of the excitation feedthrough into the receive chain helps towards acquiring the fundamental frequency response of the superparamagnetic iron oxide nanoparticle (SPIONs), which is beneficial for quantitative measurements. As one approach, particularly suited for multi-frequency MPI (mf-MPI), tuning coil loading (TCL) has been shown to effectively reduce the feedthrough at the fundamental frequency way below the levels achievable with e.g. gradiometer coil arrangements alone. In this work, the effect of TCL on higher frequency components is evaluated by capturing the harmonics of a real particle signal, acquired by measurements at different excitation frequencies. A comparison between gradiometer-only and combined gradiometer plus TCL operation is presented. It is shown that TCL does not negatively impact the harmonics, hence provides an effective feedthrough suppression while preserving the higher frequency performance.
Copyright (c) 2026 Harald Radermacher, Magdalena Kunz, Franziska Schrank, Dennis Pantke, Florian Mueller, Volkmar Schulz https://creativecommons.org/licenses/by/4.0
Comparison of human-scale MPI system concepts using a 3D arbitrary-waveform magnetic particle spectrometer
In the field of Magnetic Particle Imaging (MPI) hybrid methods are utilizing the simplicity and high SNR of magnetic particle spectrometers to complement the imaging aspect by characterizing particles and measuring system matrices for fast system calibration. In this contribution we utilized the flexibility of our 3D arbitrary-waveform magnetic particle spectrometer to measure the system functions of three MPI scanner concepts inspired by clinical-scale head-sized MPI systems. Using these system matrices we are able the compare reconstructed images under the same noise, particle and reconstruction conditions gathering first qualitative insights into the imaging properties of the different scanners.
Copyright (c) 2026 Justin Ackers, Niklas Hackelberg, Tobias Knopp, Matthias Graeser https://creativecommons.org/licenses/by/4.0
Multi-Color MPI via Field-Free Line Projections: A Linear Mixed Inverse Approach
Multi-color magnetic particle imaging (MPI) has been extensively studied for vascular intervention and tumor imaging, primarily via system matrix or relaxation-based methods. Field-free line (FFL) projection imaging avoids extensive calibrations of system matrices but encounters signal superposition in multi-color setups. We model this challenge as a linear mixed inverse problem, adapting a benchmark network from the blind source separation domain. This approach achieves effective separation on a vessel-aneurysm phantom, demonstrating promising applications.
Copyright (c) 2026 Xueying Liu, GH L, Ziwei Chen, Haicheng Du, Jie Tian, Yu An https://creativecommons.org/licenses/by/4.0
Spherical harmonic-based receive coil array for a head MPI system
A gradiometric receive coil is practically the modern standard in MPI. Although such a structure is one of the reliable and most effective ways of isolating the receive circuits from the influence of drive fields, it is challenging to implement it for the spatial sensitivity directions orthogonal to the cylinder axis of an MPI scanner. In this work, we demonstrate a concept of matrix coils based on spherical harmonic spatial sensitivity profiles. Our approach permits us to expand the number of independent receive channels in our head-sized MPI system to seven (and potentially more), while preserving important gradiometric characteristics of each channel.
Copyright (c) 2026 Onurcan Topcu, Egor Kretov , Justin Ackers , Patricia Römer, Niklas Hackelberg, Haozhe Wang, Florian Thieben, Takashi Yoshida, Mandy Ahlborg, Tobias Knopp, Matthias Graeser https://creativecommons.org/licenses/by/4.0
Magnetic particle imaging (MPI) is an emerging preclinical imaging modality that offers several notable advantages, including excellent biosafety, high sensitivity, and superior image contrast. To further improve spatial resolution and expand the effective field of view, this study proposes a novel X-ray based MPI approach. In this method, magnetic nanoparticles are employed as contrast agents for X-ray imaging, while an external magnetic field is applied to modulate their X-ray absorption coefficient. Consequently, the spatial distribution of the magnetic nanoparticles can be translated into quantifiable variations in X-ray beam intensity. A proof-of-concept experiment was conducted using a custom-built, simplified device to preliminarily validate the feasibility of the proposed method, and the observed imaging behavior was interpreted within the framework of magnetic dipole–dipole interaction theory. This X-ray based MPI method demonstrates significant potential for practical application, offering a new technical paradigm that may advance the translational development of MPI toward clinical implementation.
Copyright (c) 2026 Xinchao Cui, Jiantao Chen, Wenzhong Liu https://creativecommons.org/licenses/by/4.0
The “harmoMPI” Project: Harmonizing Magnetic Particle Imaging Through Scanner-Independent Functional Phantoms
Magnetic Particle Imaging (MPI) is an emerging tomographic modality recognized for its capability of directly detecting magnetic nanoparticles (MNPs), enabling real-time 3D imaging with high sensitivity. Since its introduction in 2005, various preclinical MPI scanners have been developed, but cross-platformcomparisons lack due to missing standardized phantoms and operation protocols. Recently, efforts towards development of human-sized MPI have intensified. To facilitate the transition beyond the preclinical research phase, harmonization of MPI technology is essential. Within the "harmoMPI" project, we aim to develop platform-independent, modular phantoms that enable reliable assessment of key performance parameters for a consistent performance evaluation across different MPI systems. With the support from the MPI research community, the "harmoMPI" initiative aims to harmonize MPI technology, advance collaboration research, and pave the path toward clinically relevant applications.
Copyright (c) 2026 Bruno Kluwe, Marcus Löffler, Yaser Hadadian, Christian Fiedler, Silvio Dutz, Frank Wiekhorst https://creativecommons.org/licenses/by/4.0
MPI quantification of magnetically labeled extracellular vesicles in mouse heart following myocardial infarction
This study aims to develop magnetically labeled iPSC-derived extracellular vesicles (magneto-EVs) for MRI/MPI and myocardial repair in a theranostic manner. Using optimized electroporation and purification protocols, we prepared magneto-EVs with high SuperSPIO20 loading efficiency (1.77 ng Fe/10? EVs) and well-preserved therapeutic effects. In vitro MPI results reveal that the detectability of magneto-EVs is ~1 × 109 EVs/mL. In vivo MPI shows that MPI can detect magneto-iPSC-EVs injected intramyocardially in mouse hearts for up to 7 days following myocardial infarction. MPI quantification showed that 32% of injected EVs remained in the heart after 24 hours, with a further ~50% decrease by day 7, indicating progressive clearance or biodegradation of magneto-EVs from the injected site. Despite this low retention and rapid clearance, magneto-EVs led to significant improvement in left ventricular ejection fraction (37.3% increase) and scar formation (61.0% reduction). This theranostic EV imaging platform enables quantitative MPI monitoring of EV delivery and predicting therapeutic outcomes.
Copyright (c) 2026 Wenshen Wang, Zheng Han, Safiya Aafreen, Cristina Zivko, Olesia Gololobova , Vasiliki Machairaki, Kenneth Witwer, Geoffrey Cotin, Delphine Felder-Flesch, Jeff Bulte, Robert Weiss, Guanshu Liu https://creativecommons.org/licenses/by/4.0
In vivo MPI/BLI tracking of genome-edited-patient derived neural precursor cells in a transgenic ALS mouse model
Amyotrophic lateral sclerosis (ALS) caused by superoxide dismutase 1 (SOD1) mutations may benefit from a gene-edited induced pluripotent stem cell (iPSC)-based therapy, provided cell fate after administration can be monitored precisely, non-invasively and longitudinally for effective optimization. This study evaluated tracking of neural precursor cells (NPCs) derived from gene-edited iPSCs using magnetic particle imaging (MPI) and bioluminescence imaging (BLI). Luciferase-expressing Nanoluc-NPCs were magnetically labeled and stereotaxically transplanted into the motor cortex of SOD1G93A transgenic mouse models. BLI confirmed luciferase activity and cell viability, while MPI enabled quantitative tracking of labeled cells in vivo. Regression analysis estimated an iron content of ~10 pg per cell, with MPI-derived cell numbers aligning closely with injected values. BLI signals persisted for two weeks, and behavioral testing revealed delayed disease progression for treated vs. non-treated controls. These results demonstrate successful non-invasive visualization and quantification of transplanted NPCs, supporting the use of MPI/BLI for imaging-guided cell therapies in ALS.
Copyright (c) 2026 Ali Shakeri-Zadeh, Asif Itoo, Shreyas Kuddannaya, Cristina Zivko, Vasiliki Mahairaki, Jeff Bulte https://creativecommons.org/licenses/by/4.0
In vivo MPI tracking of ICV-injected mesenchymal stem cells in an EAE mouse model of multiple sclerosis
Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Human mesenchymal stem cells (hMSCs) provide therapeutic benefits through their immunomodulatory and neuroprotective effects. This study investigated the biodistribution of magnetically labeled hMSCs following intracerebroventricular (ICV) injection in the chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS in vivo using magnetic particle imaging (MPI) in combination with magnetic resonance imaging (MRI) and computed tomography (CT). Our imaging analyses revealed increased MPI signal in both the cerebellum and spinal cord by day 7 post-injection, suggesting distribution of hMSCs via cerebrospinal fluid (CSF) flow. These findings highlight the value of MPI as a quantitative and specific non-invasive tool for longitudinal cell tracking in vivo and provide important insights into the optimization of stem cell–based therapies for MS.
Copyright (c) 2026 Kritika Sood, Aline Thomas, Asif Itoo, Jeff Bulte, Ali Shakeri-Zadeh https://creativecommons.org/licenses/by/4.0
MPI reveals MPI reveals injection route-dependent biodistribution of human mesenchymal stem cells in EAE mice
Magnetic particle imaging (MPI) enables real-time and quantitative tracking of magnetically labeled therapeutic cells with remarkable sensitivity and no tissue background. Human mesenchymal stem cells (hMSCs) possess potent immunomodulatory and regenerative effects in multiple sclerosis (MS), but their efficacy depends on precise delivery and homing to inflamed neural tissues. Using an experimental autoimmune encephalomyelitis (EAE) mouse model for MS, we dynamically tracked ferucarbotran-labeled hMSCs following four sequential intravenous (IV) or intra-arterial (IA) injections. Minute-timescale MPI acquisitions revealed that IV-injected cells were retained predominantly in the pulmonary space with gradual redistribution to the spleen and liver, consistent with remote immunomodulatory activity via splenic engagement. In contrast, IA delivery achieved immediate cerebral accumulation with strong brain signal and concurrent splenic uptake. These findings demonstrate route-dependent biodistribution patterns and confirm the usefulness of MPI for longitudinal assessment of stem cell delivery.
Copyright (c) 2026 Ali Shakeri-Zadeh, Kritika Sood, Aline Thomas, Chengyan Chu, Piotr Walczak, Jeff Bulte https://creativecommons.org/licenses/by/4.0
Reduced-Order Modeling of Nanoparticle Magnetization Dynamics
The coupled Brown-Néel rotation model formulates the nanoparticle magnetization dynamics as a system of ordinary differential equations that are computationally demanding to solve. In this work, we propose utilizing a proper orthogonal decomposition approach for reduced-order modeling of magnetization dynamics, providing significant computational speedup while preserving accuracy.
Copyright (c) 2026 Sevil Dilge Gulsun, Asli Alpman, Emine Ulku Saritas https://creativecommons.org/licenses/by/4.0
Detection of Pseudomonas aeruginosa in Whole Blood using a portable Magnetic Particle Spectrometer - a feasibility study
Rapid identification of WHO critical priority pathogens, such as Pseudomonas aeruginosa, is essential for managing sepsis, where standard blood cultures cause diagnostic delays of 24-72 hours. To address this, we developed a rapid, culture-independent magnetic immunoassay using a portable Magnetic Particle Spectroscopy (MPS) device for the direct detection of P. aeruginosa in blood. We evaluated two SPION formulations and found that our developed formulation, SPION-152, demonstrated excellent specificity, generating a strong signal change with virulent P. aeruginosa strains while showing negligible cross-reactivity with E. coli. Specificity for a virulence-associated factor was confirmed using a knockout mutant. These findings validate the MPS platform as a promising tool for accelerating pathogen identification in patients with suspected sepsis.
Copyright (c) 2026 Lukas Heinen, Alexander Simonis, Jan Rybniker, Johanna Günther, Patrick Vogel, Christina Janko, Christoph Alexiou, Stefan Lyer, Rainer Tietze https://creativecommons.org/licenses/by/4.0
Strong magnetic interaction potentially favors smaller particles in MPS
Magnetic nanoparticles (MNPs) are pivotal in biomedical applications such as imaging, hyperthermia, and biosensing due to their distinct relaxation dynamics under alternating magnetic fields (AMF). In vivo, MNPs are gradually internalized into cellular and tissue environments, where decreasing interparticle distances – resulting from aggregation, target binding, and dense packing – alter their magnetic response to AMF. These changes amplify magnetic dipole particle-particle interactions (pp-IA) among MNP, notably impacting their relaxation behavior. In this work, we investigate the effect of pp-IA on magnetic particle spectroscopy (MPS) via stochastic simulations coupling Néel and Brownian relaxation mechanisms. Our preliminary results provide evidence that at average interparticle distances below ~50 nm, MNPs with smaller core size (16 nm) yield stronger MPS signals than larger cores (20–28 nm).
Copyright (c) 2026 Mohamad Bilal Abbas, Merle Kott, Hans-Joachim Krause, Ulrich Engelmann https://creativecommons.org/licenses/by/4.0
Sequence-to-Image Reconstruction in Magnetic Particle Imaging: A BiLSTM Proof of Concept
Magnetic Particle Imaging (MPI) produces voltage signals that are periodic and highly correlated across time. Classical deep-learning reconstruction methods generally treat these signals as static feature vectors. In this work, we explore a purely data-driven sequence-to-image approach using a bidirectional long short-term memory (BiLSTM) network followed by a lightweight convolutional neural network (CNN). The model directly maps 1D MPI-signals to 2D images. We evaluate performance using a synthetically generated, trajectory-encoded augmented MNIST dataset, and analyse robustness under different signal-to-noise ratios (SNR). Results demonstrate that the BiLSTM architecture successfully reconstructs image structure and remains robust even at low SNR levels, highlighting the potential of sequence modelling for future MPI reconstruction.
Copyright (c) 2026 Anselm von Gladiß, Niranjan Thuruthiyil Balakrishnan, Jan Herschel https://creativecommons.org/licenses/by/4.0
Theoretical Verification of Coil-Array-Based 3D Magnetic Particle Imaging Technology
To enable real-time three-dimensional (3D) magnetic particle imaging (MPI) based on the field-free line (FFL), we propose a novel 3D MPI strategy that employs tomographic encoding through the spatially specific sensitivities of a receive coil array. Based on the spatially specific sensitivity encoding (SSSE) principle of the multi-channel receive coil array, 3D reconstruction can be achieved with only a 2D translational scan of the magnetic FFL. This approach reduces the scanning dimensionality by one compared to conventional parallel-beam tomography, offering a new paradigm for rapid, real-time 3D imaging. During reconstruction, multi-channel projection images transform the 3D inverse problem into a series of 1D inverse problems, significantly reducing computational complexity. Finally, the feasibility of sensitivity?based spatial encoding was validated in simulation experiments, demonstrating its broad application prospects and innovative value for 3D MPI imaging.
Copyright (c) 2026 Ning He, Jiawei Hu, Yuzhou Wang, Yao Tong, Dong Liang, Dinghong Duan, Kai Liu, Yihan Wang, Shouping Zhu https://creativecommons.org/licenses/by/4.0
The multi-color relaxation wall: fundamental limits of spectral separation in physics-based MPI
Multi-color Magnetic Particle Imaging (MPI) differentiates biological processes by exploiting particle-specific relaxation times, but conventional approaches require extensive calibration. We extend Sanders' physics-based framework with particle-specific Debye operators, enabling calibration-free multi-color reconstruction. Simulations with Momentum scanner parameters separate free-circulating (tau1 = 1 microsecond) and tissue-bound (tau2 = 20 microseconds) particles, achieving 95.9% and 78.4% purity and quantifying a frequency-domain trade-off: long-tau responses suffer attenuation when omega*tau >> 1, yielding approximately 15 dB difference at 45 kHz relative to short-tau particles. The formulation links tau-ratios to spectral separability (S = 0.375, rho = 0.625) and provides practical guidance for selecting particles and protocols without particle-specific calibration, applicable to preclinical and clinical MPI studies.
Copyright (c) 2026 Seungjun Oh, Hafiz Ashfaq Ahmad, Muhammad Umar Tahir, Jungwon Yoon https://creativecommons.org/licenses/by/4.0
On the Optimization of Sinogram-based Calibration
Sinogram-based calibration in Magnetic Particle Imaging (MPI) using a 3D field free line (FFL) trajectory offers high-quality system matrices. This approach involves repeating the imaging trajectory at multiple trajectory offsets in sinogram domain. However, transitions between these repetitions can introduce unwanted spectral components (USCs), potentially overloading transmit electronics. This work investigates and compares three strategies, namely stop & go, circularly-shifted, and all-ramp, for their impact on spectral purity. Simulations demonstrate that the circularly-shifted design maintains trajectory stability and significantly suppresses USCs, while the all-ramp approach achieves the shortest calibration time and minimal USCs at the cost of a slight infidelity to the actual trajectory. These results highlight trade-offs between spectral purity, trajectory accuracy, and efficiency, providing practical guidelines for optimizing sinogram-based calibration.
Copyright (c) 2026 Serhat Ilbey, Jochen Franke https://creativecommons.org/licenses/by/4.0
Unsupervised deep-learning approach for time domain signal denoising in MPI
Denoising is crucial in Magnetic Particle Imaging (MPI) since the measured signals are inherently affected by noise and distortions that degrade the reconstruction quality. This work explores an unsupervised deep-learning approach for time-domain denoising of real-world MPI data, which is based on a Wasserstein Generative Adversarial Network (WGAN). The results show that unsupervised deep learning-based denoising can enhance the signal quality of 1D MPI data by increasing the sensitivity and reducing reconstruction artifacts.
Copyright (c) 2026 Felix Dahms, Volkmar Schulz, Franziska Schrank https://creativecommons.org/licenses/by/4.0
Degradation Consistent Conditional Diffusion Model with Frequency Alignment for 3D Mag-netic Particle Image Enhancement
Magnetic Particle Imaging (MPI) provides quantitative visualization of magnetic nanoparticle distributions but suffers from limited spatial resolution and anisotropic blurring due to system nonlinearities and hardware imperfections. To address the low-resolution issues caused by various noise sources, we propose a Degradation-Consistent Conditional Diffusion Model (DCCDM) for three-dimensional (3D) MPI image super-resolution. The proposed model introduces two physically interpretable constraints: a degradation-consistency loss, utilizing a degradation operator to ensure that the reconstructed high-resolution volume remains consistent with the observed low-resolution data, without requiring a known system matrix, and a frequency-alignment regularization, enforcing structural fidelity in the low-frequency band and detail enhancement in the high-frequency band. Experiments on simulated 3D MPI datasets demonstrate that DCCDM achieves superior performance compared with existing CNN-, GAN-, and diffusion-based models.
Copyright (c) 2026 Zhiming Qiu, Zechen Wei, Jiaxin Zhang, Jie Tian, Hui Hui https://creativecommons.org/licenses/by/4.0
Towards Addressing Nanoparticle Relaxation in Model-Based Reconstruction
Magnetic Particle Imaging (MPI) is a tracer-based imaging modality that uses superparamagnetic nanoparticles as tracer. The Langevin model is a simple model that is capable of capturing the overall relation between the measured signal and the particles, but it ignores relaxation effects. Relaxation effects can be accounted for in the Debye model, which introduces a relaxation parameter ?, representing the delay in the alignment of the nanoparticles to the magnetic field. Starting from the Debye model, we propose a relaxation adaption step to account for the delay ? in model-based reconstructions that use the Langevin model.
Copyright (c) 2026 Vladyslav Gapyak, Thomas März, Andreas Weinmann https://creativecommons.org/licenses/by/4.0
Magnetosomes: The future of theranostics?
Magnetic nanoparticles serve as essential tracers in biomedical applications, including diagnostics such as magnetic particle imaging (MPI) and therapies like magnetic fluid hyperthermia (MFH). However, meeting the physicochemical requirements of both applications within a single nanoparticle system remains challenging. Magnetosomes, a novel class of magnetic iron oxide nanoparticles biosynthesized by bacteria, offer a promising solution, as their magnetic properties can be tuned through genetic engineering. Here, magnetosomes are investigated for dual functionality as MPI tracers and MFH heat mediators, highlighting their potential as a theranostic platform.
Copyright (c) 2026 Oliver Buchholz, Marina Dziuba, Simon Markert, Dirk Schüler, Ulrich G. Hofmann, Serhat Ilbey, Jochen Franke, Frank Mickoleit https://creativecommons.org/licenses/by/4.0
Oxygen vacancy-regulated iron oxide nanoparticles for magnetic particle imaging
Magnetic particle imaging (MPI) is an emerging medical imaging technique with the advantages of high sensitivity, linear quantitation, and no ionizing radiation. The magnetic nanoparticles play a vital role in MPI. Hence, we investigated the effects of oxygen vacancies in iron oxide nanoparticles (IONPs) on MPI imaging performance. We developed IONPs with different oxygen vacancies and the results showed that as the oxygen vacancies of IONPs increased, the MPI signal initially increased and then decreased. And IONPs with two oxygen vacancies exhibited the optimal MPI imaging performance, which providing effective evidence for designing high-performance IONPs.
Copyright (c) 2026 Qian Liang, Yuling Bai, Zhenqi Jiang, Jie Tian, Yang Du https://creativecommons.org/licenses/by/4.0
Enhanced brain retention time of MPI tracer via antibody conjugation
Hyperthermia guided by Magnetic Particle Imaging (MPI) is an emerging technique for targeted thermal therapies, including blood–brain barrier opening and localized tumor ablation. However, this technique works best for locally injected magnetic nanoparticles, but faces limitations with intravenous administration. Floating with circulation, the tracers often traverse the target region too quickly, succumbing to heat loss by blood cooling, thus failing to achieve sufficient localized thermal doses. This limitation reduces the efficacy of MPI-guided hyperthermia for precision applications in sensitive tissues such as the brain. Here, we propose a strategy to immobilize the magnetic nanoparticles at the brain capillary level via antibody conjugation specific to the vascular endothelium allowing future localized heating experiments. We present initial experimental proof showing the feasibility of this approach by increasing retention times of particles in the brain evidenced by extended local blood half-life.
Copyright (c) 2026 Sébastien Bär, Oliver Buchholz, Christian Münkel, Jochen Franke, Ulrich G. Hofmann https://creativecommons.org/licenses/by/4.0
Dendronized iron oxide: SUPERSPIO20 as MPI tracer and magnetic hyperthermia agent
The rise of MPI technology has led to the growing development of equipment requiring the use of an optimized magnetic tracer for increased sensitivity and resolution. In addition, MPI technology paves the way for truly targeted tumour treatment using the field free point approach for focused magnetic hyperthermia. The need for a theranostic tracer is therefore essential for further preclinical and clinical development. Among the many methods of synthesizing nanoparticles, thermal decomposition is the method of choice for perfect control of the size, distribution, shape and composition of nanoparticles. Mastery of this method has led to the development of SuperSpio20, a dendronised iron oxide nanoparticle whose 20 nm iron oxide core has a first-order MPI signal and optimized heat release for focused mild hyperthermia. The controlled dendronized coating maintains a hydrodynamic diameter of less than 35 nm, allowing intravenous injection. This design also allows the labelling of therapeutic cells without the need for a transfection agent for the development of MPI-tracked cell therapies.
Copyright (c) 2026 Delphine Felder-Flesch, Laura Streit, Sara Jakimoska, Isis Blanchard, Samuel Valable, Geoffrey Cotin https://creativecommons.org/licenses/by/4.0
Influence of System Matrix Concentration and Frequency Selection on Reconstructed MPI Signals
In Magnetic Particle Imaging (MPI), the system matrix (SM) characterizes the spatial encoding properties of the imaging system and the magnetic nanoparticle response. Ideally, for linear particle magnetization behavior, the concentration at which the SM is measured should not affect the reconstructed image. In this study, two SMs recorded with tracer concentrations of 8.5 mg(Fe)/ml and 1.92 mg(Fe)/ml were investigated. We show that, although the same SM is used, reconstruction discrepancies occur when the frequency coverage differs. We therefore propose to determine the usable frequency components based on the lower concentration SM to ensure a consistent reconstruction basis.
Copyright (c) 2026 Sathurya Jegatheeswaran, Hanna Meenen, Ksenija Gräfe, Thorsten M. Buzug https://creativecommons.org/licenses/by/4.0
A Progressive Transformer-GAN Framework for System Matrix Recovery in Magnetic Particle Imaging
Magnetic Particle Imaging (MPI) is an emerging non-invasive high-resolution technique, but its practicality is constrained by time-consuming repetitive calibration of the System Matrix (SM) when parameters, particle types, or environments change. To address this, we propose TP-GAN, a Transformer-based Progressive GAN for MPI SM super-resolution. It integrates a feature enhancement module to stabilize SM’s physical structure and capture cross-scale correlations, with multi-loss optimization improving consistency between super-resolution and real high-resolution SM, as well as accuracy and anti-noise performance. Experimental results show TP-GAN outperforms existing methods, reducing reliance on repeated calibration and advancing MPI’s biomedical applications.
Copyright (c) 2026 Lizhi Zhang, Jintao Li, Xiaowei He, Hongbo Guo https://creativecommons.org/licenses/by/4.0
In vivo MPI of HER2-targeted tumor SPIO uptake is hindered by its current dynamic signal range
Trastuzumab (Tz, herceptin) is a clinically approved monoclonal antibody targeting HER2 on tumor cells, making it an attractive bioligand for specific tumor targeting of superparamagnetic iron oxide (SPIO) nanoparticles. We investigated if Tz-conjugated SPIO could be used for MPI of HER2+ breast tumors. Successful conjugation and preservation of specific HER2-binding of Tz after SPIO conjugation was confirmed in vitro by immunostaining and MPI. Following intravenous injection of Tz-SPIO in a transgenic (spontaneously orthotopic) HER2+ breast cancer mouse model, in vivo MPI was unable to show a distinguishable tumor signal due to the close anatomical proximity of high-signal organs (i.e., liver, spleen, and lungs) to the thoracic tumor, unlike in subcutaneous models. The pulmonary signal disappeared by day 3, indicating SPIO redistribution and/or clearance. However, ex vivo MPI confirmed that tumor accumulation of Tz-SPIO was approximately 1.7- to 3.7-fold higher than that for IgG1-SPIO and unconjugated-SPIO controls, respectively. We conclude that the limited dynamic range of the current MPI technology prevents successful in vivo tumor visualization at low tumor to non-tumor tissue ratios, which was 1:8 to 1:15 in our studies. While antibody-mediated SPIO tumor targeting works in principle, there is an urgent need to develop methods for increasing the dynamic range of MPI.
Copyright (c) 2026 Asif Itoo, Ali Shakeri-Zadeh, Janani Gurumurthy, Preethi Korangath, Sudath Hapuarachchige, Dmitri Artemov, Robert Ivkov, Jeff Bulte https://creativecommons.org/licenses/by/4.0
A correlation-constrained SNR frequency selection algorithm for magnetic particle imaging reconstruction
System matrix-based reconstruction is a commonly used method in magnetic particle imaging (MPI). However, due to the large memory requirements, lengthy processing times, and ill-posed nature of the system matrix, computational feasibility remains limited to perform reconstruction using the entire matrix. The most common approach involves frequency component selection based on signal-to-noise ratio (SNR), where a limited number of frequency components are chosen for reconstruction. This method accelerates processing while preserving critical reconstruction information. However, selection based solely on SNR risks discarding critical image information, and frequency components with high SNR may exhibit redundant information. Therefore, this paper proposes a correlation-constrained SNR frequency selection algorithm. Its objective is to select high SNR frequency components to ensure the reconstructed image's SNR while prioritizing mutually independent components to better recover image details. Experimental results on real data demonstrate that the proposed algorithm demonstrates superior reconstruction fidelity.
Copyright (c) 2026 Wenjing Jiang, Jinzhuang Xu, Xiaoxue Wang, Ning He, Moritz Wildgruber, Xiaopeng Ma https://creativecommons.org/licenses/by/4.0
Efficient solvers for coupled Brown-Néel Fokker-Planck equations II
Solving the inverse problem in magnetic particle imaging (MPI) relies on efficient and accurate solutions to the forward model. In [1] we proposed a numerical method for solving the convection-dominated Fokker-Planck equation arising from coupled Brownian and Néel relaxation mechanisms. Furthermore, this method tackles the parameter dependence coming from the potentially large number of physical parameter combinations. In this work, we present numerical results for the coupled problem using the joint angular-temporal discretization of this partial differential equation (PDE) and a reduced basis (RB) method for the parameter dependence from [1]
Copyright (c) 2026 Manfred Faldum, Franziska Schrank, Volkmar Schulz, Markus Bachmayr https://creativecommons.org/licenses/by/4.0
Magnetic particle imaging of tumor retention and leakage of magnetic nanoparticles reveals high inter-subject variability
Intratumoral (i.t.) injection of magnetic nanoparticles (MNPs) is a clinically relevant strategy for localized therapy, including magnetic fluid hyperthermia (MFH). However, the fate of i.t.-injected MNPs remains poorly characterized. Here, we employed magnetic particle imaging (MPI) to quantitatively and longitudinally monitor MNP retention and leakage of i.t.-Synomag®-D70 in a mouse subcutaneous 4T1 breast tumor model. Mice (n=4) were scanned serially (15 min to 8 day) using 2D MPI with fiducial calibration. At day 8, 3D MPI and CT co-registration were performed, followed by ex vivo imaging. A strong linear calibration (R²=0.967) between MNP concentration and MPI signal enabled accurate iron quantification. All tumors showed strong initial MPI signal with an 1.8 to 3.0-fold signal reduction by day 8, indicating gradual tumor clearance. Liver and spleen uptake could only be observed in 2 out of 4 mice, while none of the other major organs showed uptake. The high inter-subject variability in MNP tumor retention calls for integrating MPI quantification for developing individualized MFH treatment plans.
Copyright (c) 2026 Ali Shakeri-Zadeh, Asif Itoo, Janani Gurumurthy, Preethi Korangath, Robert Ivkov, Jeff Bulte https://creativecommons.org/licenses/by/4.0
Coordinate transformations for magnetic fields’ solid spherical harmonic coefficients
Magnetic particle imaging fundamentally relies on magnetic fields, so accurate characterization of the fields is crucial for various applications, such as sequence planning or model-based reconstructions. Magnetic fields can be compactly represented by solid harmonic expansions, whose coefficients efficiently describe the field distribution. However, in practice, the coordinate systems of measurement devices are not always perfectly aligned with the scanner's coordinate system, complicating direct comparison and integration of measured data from different setups. In this work, we present methods for transforming solid harmonic coefficients under translations, rotations, and point reflections. These transformations enable consistent mapping of field representations into a common coordinate system, allowing direct comparison of magnetic fields obtained in different coordinate frames.
Copyright (c) 2026 Marija Boberg, Fynn Foerger, Tobias Knopp, Martin Möddel https://creativecommons.org/licenses/by/4.0
Fast Multi-Patch System Matrix Calibration in MPI Using Reference Patch Data
In multi-patch magnetic particle imaging (MPI), optimal reconstruction performance using the joint reconstruction approach requires acquiring a complete system matrix (SM) for each patch, which leads to a substantial calibration burden. To address this issue, this study proposed a reference-based multi-patch SM fast calibration method. Leveraging the inherent correlations among SMs corresponding to different patches, we fully measure the complete SM only one reference patch, while for the other patches, data are measured at a limited number of positions. The complete SMs of the remaining patches are then reconstructed by referencing the complete SM of reference patch. Experimental results demonstrate that the proposed method significantly reduces the calibration time while achieving high-quality reconstruction of SMs for the other patches.
Copyright (c) 2026 Pengyue Guo, Kai Liu, Yihan Wang, Shouping Zhu https://creativecommons.org/licenses/by/4.0
Topology Considerations for an Iron-Core Coil Module Field Generator
The selection-field generator of a Magnetic Particle Imaging (MPI) scanner is typically the system’s largest power consumer. For potential use in intensive care units, it would be highly desirable to operate MPI scanners from a standard wall outlet without dedicated high-power infrastructure. Several concepts for more efficient selection-field generation have been proposed in recent years. In this work, we propose a novel generator design based on an array of soft-iron core coils arranged at an angle around the scanner bore. This geometry reduces overall electrical power demand while enabling gradient strengths of up to 0.5 T/m. The design was simulated and optimized using magnetostatic simulations in COMSOL Multiphysics. To ensure reliable modeling of the soft-iron cores, prototype coils were built and their magnetic fields were measured, providing experimental validation of the simulation models.
Copyright (c) 2026 Fynn Foerger, Eric Aderhold, Jan-Philipp Scheel, Matthias Graeser, Mandy Ahlborg, Tobias Knopp https://creativecommons.org/licenses/by/4.0
Design considerations and approaches for new MPI Tracers
The development of suitable magnetic nanoparticles as tracers for MPI faces multiple obstacles. Beyond MPI-specific optimization, properties that are of utter importance for clinical approval like biocompatibility, colloidal stability in blood, synthesis reproducibility and upscalability of the process have to be taken into account. Overcoming these challenges will require interdisciplinary efforts. The Section of Experimental Oncology and Nanomedicine (SEON) is dedicated to develop SPIONs that can be translated into clinical use. We have already shown that we developed a save contrast agent for MRI, are capable of upscaling particle precipitation techniques and span a wide portfolio for non-regulatory preclinical testing of SPIONs in vitro and in vivo. Together with partners from the pharmaceutical industry, we will also be capable of bringing such processes into preclinical and clinical trials.
Copyright (c) 2026 Rainer Tietze, Lukas Heinen, Stefan Lyer, Christoph Alexiou https://creativecommons.org/licenses/by/4.0
Multi-Task MPI real-collected FFL-based dataset
Deep learning, owing to its potent nonlinear fitting capacity, has been increasingly applied to magnetic particle imaging (MPI)-related tasks to enhance the system performance. Nevertheless, the efficacy of deep learning models is contingent upon the availability of extensive training data. Currently, the availability of real-collected datasets suitable for deep learning training and testing remains limited, thereby compromising the generalizability and practical efficacy of data-driven approaches in real-world deployment scenarios. To mitigate this limitation, the proposed MPI-image dataset supports multiple image-centric tasks including anisotropy analysis and denoising, thereby facilitating the development and validation of deep learning approaches under real-world conditions.
Copyright (c) 2026 Yuanduo Liu, Zechen Wei, Liwen Zhang, Xin Yang, Jie Tian, Hui Hui https://creativecommons.org/licenses/by/4.0
Deep image prior for alternating direction method of multipliers reconstruction of experimental magnetic particle imaging data
This work presents an on-the-fly training Deep Image Prior (DIP) integrated into an Alternating Direction Method of Multipliers (ADMM) algorithm for Magnetic Particle Imaging (MPI) system-matrix reconstruction. Experimental data results indicate competitive quality and robustness, supporting the approach as a practical alternative to classical Tikhonov.
Copyright (c) 2026 Antonios Nikolakis-Plytzanopoulos, George A. Kastis, Jing Zhong, Nikolaos Dikaios https://creativecommons.org/licenses/by/4.0
An Experimental Study: Multi-channel Ring Receive Coil for Magnetic Particle Imaging
In compact-bore MPI systems, the commonly used Opposed-pair Coil suffers from azimuthal dead zones and an insufficient filling factor. We propose a Multi-channel Ring Coil that tiles the bore circumferentially with small, interleaved elements, expanding the sensitive coverage area without increasing volume, thereby improving uniformity and sensitivity. In experiments using a magnetic dipole coil for frequency sweeps, the proposed array—under equal-volume constraints—yields a 58.9\% increase in signal amplitude and a 70.7\% improvement in uniformity over the Opposed-pair baseline. Moreover, each channel in the ring provides multi-angle directional information, offering richer azimuthal inputs for graph-neural-network–based array reception analysis in the future.
Copyright (c) 2026 Gen Shi, Ziwei Chen, Haoran Zhang, Zhongwei Bian, Hui Zhang, Jie Tian https://creativecommons.org/licenses/by/4.0
Background-free reconstruction in magnetic particle imaging via differential offset fields
Magnetic particle imaging (MPI) is a promising molecular imaging technique that enables quantitative visualization of the distribution of magnetic nanoparticles (MNPs). Yet, background signal affects the accurate quantitative assessment of MNPs. To suppress background signal, a common practice is to initially measure the background and subtract it during subsequent MNPs signal acquisition. However, frequent background measurements not only reduce imaging efficiency but can also introduce additional noise and repositioning artifacts. Here, we propose a background-free reconstruction method to eliminate dedicated background measurement. Specifically, a pair of differential symmetric offset fields are sequentially applied to excitation field, and the differential signal between two acquisitions yields a pure MNPs response. Simulation results show that the approach significantly enhances imaging quality compared to background measurement.
Copyright (c) 2026 Penghua Zhai, Zhongwei Bian, Weixin Xu, Jie Tian, Wei Mu https://creativecommons.org/licenses/by/4.0
Synthesis and Characterization of Superparamagnetic Polyurethane for Advanced MPI Applications
Magnetically traceable polymer composites have gained increasing attention for biomedical applications. They are particularly relevant for designing materials that can be non-invasively detected and localized using magnetic particle imaging (MPI) or analyzed using magnetic particle spectroscopy (MPS). Superparamagnetic iron oxide nanoparticles (SPIONs) are of particular interest due to their excellent magnetic properties, biocompatibility, and tunable surface chemistry. The incorporation of SPIONs into polymeric matrices such as polyurethane (PU) enables the creation of flexible, biocompatible, and magnetically active materials. Polyurethane is well-established in medical device manufacturing due to its favorable mechanical and chemical properties. However, the reproducible embedding of SPIONs within PU and the preservation of both magnetic and mechanical performance remain significant challenges. This study aimed to develop a systematic approach for integrating SPIONs into PU, focusing on reproducible synthesis, structural characterization, and magnetic evaluation of the resulting nanocomposites.
Copyright (c) 2026 Jaron Bardenhagen, Ankit Malhotra, Pascal Stagge, Eric Aderhold, Mandy Ahlborg, Kerstin Lüdtke-Buzug https://creativecommons.org/licenses/by/4.0
Domain-weighted Block Coordinate Descent for quantitative single-sided MPI reconstruction
Single-sided Magnetic Particle Imaging (MPI) provides a solution suitable for intraoperative localization. However, asymmetric coil arrangements cause nonuniform magnetic fields and depth-dependent sensitivity decay, leading to biased reconstructions. This paper proposes a domain-weighted Block Coordinate Descent (DW-BCD) algorithm for quantitative single-sided MPI reconstruction. A preliminary reconstruction estimates the signal support domain, from which weighting and regional partitioning are derived. The subsequent reconstruction combines block-wise domain-weighted and global total variation(TV) regularization. Experiments show that DW-BCD effectively reduces depth-related concentration bias, enabling accurate quantitative reconstruction of magnetic nanoparticle distributions for clinical applications of single-sided MPI.
Copyright (c) 2026 Lingwen Hou, kaixiong Yang, Yihan Wang, Shouping Zhu https://creativecommons.org/licenses/by/4.0
Progressive conditional diffusion for system matrix synthesis in magnetic particle imaging
Acquiring the system matrix (SM) under high-gradient fields in Magnetic Particle Imaging remains challenging, as it requires prolonged high-current operation. To overcome this limitation, we introduce a novel approach that synthesizes the high-gradient SM from its easier-to-obtain low-gradient counterpart using a conditional diffusion model. A progressive conditioning decay strategy is employed to effectively steer the generation of the high-gradient SM. Simulation results demonstrate that our method can successfully synthesize high-gradient SMs, thereby reducing the acquisition burden.
Copyright (c) 2026 Zechen Wei, Jie Tian, Hui Hui https://creativecommons.org/licenses/by/4.0
Simulation verification of dimensionality extension reconstruction based on field free line coding
Magnetic Particle Imaging (MPI) is an emerging imaging technology. Traditional scanning methods often use field free point (FFP) to traverse the entire imaging field of view?FOV?, or use field free line (FFL) to reconstruct images through parallel beam projection.In this study, we propose a dimensionality extension reconstruction method based on FFL line coding, this method extends the FFP along the vertical direction of its motion to form the FFL, enabling the FFR to traverse a 3D field of view during 2D scanning.This scheme enables low-dimensional scanning with high-dimensional reconstruction, which can enhance sensitivity and MPI scanning speed.This study verified the feasibility of the method through simulation experiments.
Copyright (c) 2026 Jiawei Hu, Ning He, Yuzhou Wang, Yao Tong, Dong Liang, Yihan Wang, Shoupin Zhu https://creativecommons.org/licenses/by/4.0
Randomized Greedy Kaczmarz for Multi-Contrast Magnetic Particle Imaging
Multi-contrast magnetic particle imaging allows for separating signals from different tracer materials or microenvironments from one joint measurement, yielding multi-channel images that distinguish tracers or encode properties such as temperature or viscosity. However, leakage artifacts enforce a noticeably longer application of iterative standard methods like the Kaczmarz algorithm to reach satisfactory reconstruction results. A greedy randomized version of the Kaczmarz method is adapted, showing the potential for faster recovery.
Copyright (c) 2026 Niklas Hackelberg, Patricia Römer, Kolya Ruppel, Lina Nawwas, Martin Möddel, Marija Boberg, Tobias Knopp https://creativecommons.org/licenses/by/4.0
Advances in Frequency-Mixing MPI: Block-ADMM Multi-Contrast Reconstruction for Drug-Release Thermometry and Monitoring
Magnetic particle imaging (MPI) provides quantitative maps of magnetic nanoparticle concentration and is well suited for monitoring magnetically induced hyperthermia and drug release. Building on the frequency-mixing, narrowband MPI platform previously presented at IWMPI 2024, we now focus on a reconstruction framework based on a block Alternating Direction Method of Multipliers (block-ADMM) operator formulation for efficient multi-contrast image recovery. The system employs dual-frequency excitation around 280 kHz and < 1 kHz, allowing simultaneous heating and imaging with excellent spectral separation and sensitivity. The proposed algorithm jointly inverts multiple spectral components centered at 2?fHF ± N?fLF that share a common nanoparticle distribution while exploiting their complementary spatial responses. This operator-based formulation enables near real-time reconstruction with improved resolution and noise robustness. First experimental results demonstrate temperature-dependent contrast formation, establishing a foundation for potentially quantitative MPI thermometry and feedback-controlled drug release.
Copyright (c) 2026 Thilo Viereck, Kai Luenne https://creativecommons.org/licenses/by/4.0
Development of a Compact FFL-MPI System Based on a Halbach Permanent Magnet
The high power consumption and large size of conventional Magnetic Particle Imaging (MPI) systems present significant barriers to their clinical translation. To address this challenge, we present a novel, compact MPI scanner implementation based on a Halbach permanent magnet structure. This design generates a field-free line (FFL) and achieves a gradient strength of 1.16 T/m within a 50 mm diameter bore. Experimental results demonstrate that the system successfully resolves two distinct particle points separated by 1 mm, confirming a spatial resolution better than 1 mm. Our findings position this low-power, Halbach-based MPI scanner as a promising tool for molecular imaging laboratories and a significant step towards future human-scale applications.
Copyright (c) 2026 Zhiyuan Hou, Feiyang Liao, Ya Wang, Yajie Xu, Haipeng Lv, Lilei Dong, Yilin Yang, Weixuan Feng, Jianlan Guo, Zhongyi Wu, Jian Zheng https://creativecommons.org/licenses/by/4.0
Large core & small shell particles facilitate physiological viscosity differentiation via MPS
Magnetic nanoparticles (MNP) are researched for in-vivo applications and represent a key tool in both therapy via magnetic fluid hyperthermia (MFH) and diagnostics using magnetic particle spectroscopy (MPS) and imaging (MPI). In-vivo, MNP are exposed to various physiological environments, binding to blood and cells and are thereby subjected to constantly changing conditions. In this simulative work, the performance of MNP in MPS was investigated with regard to core size, hydrodynamic size and distribution width and under different physiological viscosities of water, blood and inside cells. Our preliminary results from stochastic Neel-Brownian coupled relaxation dynamics simulations suggest that for MPS, differentiation of MNP binding states across water, blood, and intracellular environments appears feasible for MNP of large cores above 20 nm with small hydrodynamic sizes below 50 nm.
Copyright (c) 2026 Sandra Bolte, Beril Simsek, Mohamad Bilal Abbas, Hans-Joachim Krause, Ulrich Engelmann https://creativecommons.org/licenses/by/4.0
A Low-Noise Differential JFET Amplifier for Magnetic Particle Imaging
In MPIsystemsdesigned for large areas of the human body, drive fields are a significant source of interference for the receive electronics. Their influence, in addition to the direct feedthrough of the signal, can manifest itself in the form of common-modenoise,whichcanbeeffectively suppressed using filters and low-noise amplifiers with a differential architectures. In this work, we demonstrate a prototype of low-noise amplifier based on differential first stage, which works in combination with four order notch receive filter. Our preliminary results show a gain of at least 40 dB over the frequency range of 50-700 kHz, effectively covering measurable harmonic signals for head sized MPIscanner.
Copyright (c) 2026 Haozhe WANG, Egor Kretov, Onurcan Topcu, Florian Thieben, Matthias Graeser, Takashi Yoshida https://creativecommons.org/licenses/by/4.0
A practical advancement in FFL single-sided AM MPI: Achieving rabbit-scale 3D imaging without object movement in depth
For clinical applications, magnetic particle imaging (MPI) requires a large and open field of view (FOV) for flexible operation and interventional integration. Although an existing field-free-line (FFL) single-sided MPI provides high sensitivity, it typically relies on slow mechanical translation for 3D depth encoding. To overcome this limitation, we employ an amplitude modulation (AM) approach using decoupled drive and excitation coils, enabling pure electronic depth scanning up to 30 mm. The proposed rabbit-scale system achieves a 40 × 40 × 30 mm³ FOV and provides a practical solution for localized interventional applications such as sentinel lymph node biopsy.
Copyright (c) 2026 Thanh Luu Cao, Muhammad Umar Tahir, Minh Phu Bui, Hafiz Ashfaq Ahmad, Khaled Mohamed Gadelmowla, Seungjun Oh, Jungwon Yoon https://creativecommons.org/licenses/by/4.0
Design and Simulation of a Multi-Receiver Coil Array–Based Magnetic Particle Imaging System without Selection Field Generation
Conventional magnetic particle imaging (MPI) relies on high-gradient selection fields to create field-free point (FFP) or field-free line (FFL) for spatial encoding; however, these fields require high power and limit scalability. We present a field free region-less (FFR-less), fully stationary MPI configuration that achieves 3-D spatial encoding without mechanical motion. The system integrates a single excitation field with a multi-receiver coil array, providing coverage of a 100 × 100 × 50 mm³ (extendable) field of view. Simulation results confirm nanoparticle localization without selection fields or motion, demonstrating a compact, power-efficient, and scalable path toward human-scale MPI.
Copyright (c) 2026 Muhammad Umar Tahir, Thanh-Luu Cao, Seungjun Oh, Jungwon Yoon https://creativecommons.org/licenses/by/4.0