International Journal on Magnetic Particle Imaging (IJMPI)
Not a member yet
555 research outputs found
Sort by
Passive mixer model for multi-contrast magnetic particle spectroscopy
No full textFor realizing multi-contrast MPI with different types of SuperParamagnetic Nanoparticles (SPN), reconstruction of the particles’ core diameter distribution is required for various points in space. We propose a principle for distinguishing signals from SPNs of different diameters, which exploits the offset field concept already used in MPI. We show that precise reconstruction of Magnetization Curve (MC) is the key to precise reconstruction of core diameter distribution, as all information about distribution is stored in the curvature. A Passive Mixer Model is proposed in order to uniquely relate the MC to the intermodulation products in the magnetization spectra. The model does not require small signal assumption and hence does not lose accuracy in the reconstruction under large excitation fields. We show that a number of useful practical conclusions can be drawn from this model
Sparse-representation-based image reconstruction for magnetic particle imaging
No full textReconstruction methods play a significant role in magnetic particle imaging (MPI). In this study, a sparse-representation-based reconstruction method by utilizing the Gaussian radial basis functions (GRBFs) is proposed to improve the spatial resolution and artifacts of MPI images. Figure 1a shows the schematic of the proposed method. The spatial distribution of magnetic nanoparticles (MNPs) is sparsely represented by GRBFs. Consequently, the inverse problem is transformed to search for the optimal weight coefficient vector of the GRBFs. During iterative reconstruction, the center points of the GRBFs are adaptively selected. Simulation and experiments on single-harmonic-based narrowband MPI are performed to evaluate the performance of MPI images. Figure 1b shows the experimental MPI images reconstructed by the proposed method, the Kaczmarz method and the iterative Tikhonov method with gradients of 2.2 T/m and 4.4 T/m in x- and z-direction. The red dashed boxes represent the true distributions of two lines with a gap d ranging from 0.3 mm to 0.75 mm. The subfigures in Figure 1c show the three 1D curves along the white dashed lines in Figure 1b with d = 0.3 mm. It shows that the two lines with d = 0.3 mm gap can be distinguished by the proposed method, while they cannot be distinguished by the Kaczmarz and iterative Tikhonov methods. In addition, the images reconstructed by the proposed method show less artifacts compared with the other two methods. In conclusion, the proposed sparse-representation-based reconstruction method improves the spatial resolution and the artifacts for MPI
Limitations of current MPI models in the context of fluid dynamics
No full textMicromagnetic fluids are at the core of magnetic particle imaging as underlying tracer materials. They are formed when magnetic nanoparticles are suspended in a fluid such as blood, cytoplasm or water. One of the fundamental assumptions made in current MPI models is that the micromagnetic response of nanoparticles and the dynamics of the fluid transporting them are decoupled. In this contribution, we use a simplified micromagnetic model that takes this interaction into account to investigate scenarios where this assumption breaks down
Heating efficiency of commercial magnetic nanoparticles commonly used in MPI
No full textMagnetic particle imaging?MPI?uses magnetic nanoparticles(MNPs) to generate signals, and there are already several commercial MNPs available for MPI. MPI guided magnetic hyperthermia (MH) has a huge application prospect in the precision treatment of tumor. It is of great significance for MPI-guided MH to find a kind of MNPs suitable for both MPI and MH. In this work, we first tested the heating efficiency of five kinds of commercial MNPs(Micromod for Perimag,Synomag-70,Synomag-50;Magnetic Insight for Vivotrax;Nanoeast for Mag3300)commonly used in MPI at 163kHz?8mT.Of these MNPs, Mag3300 has the best heating efficiency under fixed conditions. The further test showed that Mag3300 can be heated up to at least 41.2 ? . This shows the potential of Mag3300 for MPI-guided MH under this conditions
Magnetic particle spectroscopy in two-dimension mixing-frequency magnetic fields
No full textMagnetic particle spectroscopy (MPS) is one of the most versatile tools to characterize the magnetic properties of magnetic nanoparticles (MNPs). The orientation, amplitude and frequency of excitation magnetic fields significantly affect the MPS signal of MNPs. In this study, we investigate the MPS signal of MNPs in two-dimension mixing-frequency magnetic fields with a custom-built MPS system. Figure 1a shows the schematic of the MPS system. In x direction, two solenoid coils are used to generate mixing-frequency magnetic fields, containing a high-frequency fHx and low-frequency fLx magnetic fields. In y direction, a pair of rectangular Helmholtz coils is used to generate a low-frequency fLy magnetic field. To detect the magnetic response of the MNPs, 2D detection coils in both x- and y-direction are designed. With this configuration, the custom-built system allows to comprehensively study the MPS signal of MNPs in 2D mix-frequency magnetic fields with different excitation sequences by tuning their frequencies, amplitudes and phases. Figures 1b and 1c show the simulated MPS signal in x-direction detection coil in 2D mixing-frequency magnetic fields with a low frequency fLy = 100 Hz (Fig. 1b) and fLx = 100 Hz (Fig. 1c), as well as a high frequency fHx = 10 kHz. The magnetization of the MNPs is modulated by the 2D low-frequency magnetic field. Thus, it contains different mixing-frequency components in the MNP spectra. We envisage the study of MPS signal of the MNPs in 2D mixing-frequency magnetic fields is of great significance to magnetic particle imaging and magnetic bio-sensing
Time Domain System Matrix (TD-SM) for Isotropic Resolution and Artifact Removal image reconstruction in X-space MPI
No full textMagnetic Particle Imaging (MPI) is an emerging medical imaging modality based on the non-linear response of superparamagnetic iron oxide nanoparticles (SPIONs), and imaging the concentration of the SPIONs. At present, MPI reconstruction mainly includes x-space and system matrix methods. The x-space method has an extremely fast reconstruction speed and the final reconstructed image can be seen as the result of convolution of particle distribution with point spread function (PSF), but it causes anisotropic resolution and artifacts due to the effect of anisotropic PSF. In this work, we propose a hybrid approach that combines the x-space and model-based system matrix methods to remove the PSF blur and reconstruct the isotropic resolution and artifact removal MPI images. We first build the system matrix in the time domain transformed by the ideal MPI scan model in the time domain. Then, we convert the x-space reconstruction process into a matrix operation, and subsequently combine several matrices into a system matrix (forward model). The input of this forward model is particle distribution and the output is the x-space reconstructed image, which is affected by the PSF blurring. The PSF blur removal is then converted to an inverse problem solving, which we implement using the Kaczmarz method to obtain isotropic resolution and artifact removal images. The results of simulation and phantom experiments demonstrate that our method could achieve the best isotropic resolution and image quality comparing with the standard x-space method and other PSF removal methods
Versatile superparamagnetic radiopaque nanocomplex for in vivo MPI, MRI, and CT stem cell tracking
No full textThere are currently over 800 registered clinical trials that use mesenchymal stem cells (MSCs) for tissue repair and immunomodulation. However, the fate of MSCs in vivo including their overall biodistribution and local tissue quantities is not fully known, especially how these parameters change over time. Multi-modal imaging techniques that can track cell therapeutics may allow facilitation and optimization of clinical translation therapeutic outcome. We developed a novel superparamagnetic radiopaque nanocomplex, Albumin-Bi2S3-SPIO (ABS), for labeling of MSCs. ABS exhibited excellent in MPI, MRI, and CT imaging properties, allowing tri-modal imaging use a single nanoplatform
First Human-scale Magnetic Particle Imaging System with Superconductor
No full textMagnetic particle imaging (MPI) is an emerging non-invasive molecular imaging method that can image the concentration and position of superparamagnetic iron oxide (SPIO) nanoparticles. However, the scalability of magnetic particle imaging (MPI) is the major barrier to its clinical use now. For a human bore size of MPI, it is important to achieve a high magnetic gradient for high image resolution with a large enough field-of-view (FOV) for most of body part. In this paper, we present a human-scale amplitude modulation (AM) MPI system with a bore size (200 mm) and using a superconductor that generated a high MPI magnetic gradient of up to 2.5 T/m/µ0 and a 1D-FOV of 100 mm (with a feasible 3D FOV of 140 × 140 × 100 mm). The results of this paper show that the promise of MPI for human application is not far away
MPI-guided endovascular therapy of 3D printed human aneurysms
No full textEndovascular 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
A novel method for magnetic particle optical imaging
No full textA novel method for magnetic particle imaging that exploits the change in transmitted light intensity of magnetic nanoparticles in the presence of a magnetic field allows for high resolution and sensitive imaging of magnetic nanoparticles. Since the method uses direct optical imaging, the theoretical resolution is no longer governed by the properties of the material, but depends on the optical diffraction limit. In future work, it is expected that high-resolution magnetic nanoparticle imaging in vivo will be achieved by selecting wavelengths of light that have a high penetration capacity into biological tissue