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Item type:Publication, Access status: with files , Quasi-simultaneous magnetic particle imaging and navigation of nanomag/synomag-D particles in bifurcation flow experiments(Infinite Science Publishing, 2020-09-02); ; ; ; Magnetic Particle Imaging (MPI) is used to visualize the distribution of superparamagnetic nanoparticles within 3D volumes with high sensitivity in real time. Recently, MPI is utilized to navigate micron-sized particles and micron-sized swimmers, since the magnetic field topology of the MPI scanner is well suited to apply magnetic forces. In this work, we analyze the magnetic mobility and imaging performance of nanomag/synomag-D for Magnetic Particle Imaging/Navigation (MPIN). With MPIN the focus fields are constantly switching between imaging and magnetic force mode, thus enabling quasi-simultaneous navigation and imaging of particles. In flow bifurcation experiment with a 100 % stenosis on one branch, we determine the limiting flow velocity of 1.36 mL/s, which allows all particles to flow only through one branch towards the stenosis. During this experiment, we image the accumulation of the particles within the stenosis. In combination with therapeutic substances, this approach has high potential for targeted drug delivery.Publicationtype: Journal ArticleScopus© Citations 4 109 84 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Reducing displacement artifacts by warping system matrices in efficient joint multi-patch magnetic particle imagingThe reconstruction of multi-patch magnetic particle imaging data requires a compromise between image quality and calibration time. While optimal image quality is ensured by the joint reconstruction approach, a system matrix needs to be acquired for each patch. One can reuse system matrices by shifting them in space, which decreases the calibration effort but leads to distortions due to field imperfections. In this work, we introduce a method for reducing displacement artifacts in the efficient joint multi-patch reconstruction. Based on the magnetic fields we propose a mapping that warps the central system matrix to capture the spatial displacement of off-center system matrices. In this way, we can maintain the low calibration time while significantly improving the image quality.Publicationtype: Journal ArticleScopus© Citations 8 72 99 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Towards accurate modeling of the multidimensional MPI physicsThe MPI image reconstruction problem requires, particularly for 2D and 3D excitation patterns, a measured system matrix due to the lack of an accurate model that is capable of describing the nanoparticles’ magnetization behavior in the MPI setup. Here we exploit a model based on Néel rotation for large particle ensembles and we find model parameters that describe measured 2D MPI data with higher precision than state of the art MPI models, which is also illustrated in phantom experiments. This is a short summary of the recent work (4) to which we refer to for all further details.Publicationtype: Journal ArticleScopus© Citations 1 58 94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simultaneous Magnetic Particle Imaging and Navigation of large superparamagnetic nanoparticles in bifurcation flow experiments(2020-03-15); ; ; ; Magnetic Particle Imaging (MPI) has been successfully used to visualize the distribution of superparamagnetic nanoparticles within 3D volumes with high sensitivity in real time. Since the magnetic field topology of MPI scanners is well suited for applying magnetic forces on particles and micron-sized ferromagnetic devices, MPI has been recently used to navigate micron-sized particles and micron-sized swimmers. In this work, we analyze the magnetophoretic mobility and the imaging performance of two different particle types for Magnetic Particle Imaging/Navigation (MPIN). MPIN constantly switches between imaging and magnetic modes, enabling quasi-simultaneous navigation and imaging of particles. We determine the limiting flow velocity to be 8.18 mL s−1 using a flow bifurcation experiment, that allows all particles to flow only through one branch of the bifurcation. Furthermore, we have succeeded in navigating the particles through the branch of a bifurcation phantom narrowed by either 60% or 100% stenosis, while imaging their accumulation on the stenosis. The particles in combination with therapeutic substances have a high potential for targeted drug delivery and could help to reduce the dose and improve the efficacy of the drug, e.g. for specific tumor therapy and ischemic stroke therapy.Publicationtype: Journal Article256 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , OpenMPIData: an initiative for freely accessible magnetic particle imaging dataMagnetic particle imaging is a tomographic imaging technique capable of measuring the local concentration of magnetic nanoparticles that can be used as tracers in biomedical applications. Since MPI is still at a very early stage of development, there are only a few MPI systems worldwide that are primarily operated by technical research groups that develop the systems themselves. It is therefore difficult for researchers without direct access to an MPI system to obtain experimental MPI data. The purpose of the OpenMPIData initiative is to make experimental MPI data freely accessible via a web platform. Measurements are performed with multiple phantoms and different image sequences from 1D to 3D. The datasets are stored in the magnetic particle image data format (MDF), an open document standard for storing MPI data. The open data is mainly intended for mathematicians and algorithm developers working on new reconstruction algorithms. Each dataset is designed to pose a specific challenge to image reconstruction. In addition to the measurement data, computer aided design (CAD) drawings of the phantoms are also provided so that the exact dimensions of the particle concentrations are known. Thus, the phantoms can be reproduced by other research groups using additive manufacturing. These reproduced phantoms can be used to compare different MPI systems.Publicationtype: Data PaperScopus© Citations 54 341 283 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , IVOCT catheter tracking and targeted drug delivery using magnetic particle imaging and magnetic particle navigation(2020); The modality Magnetic Particle Imaging (MPI) visualizes the quantitative distribution of magnetic nanoparticles by using static and oscillating magnetic fields. In this work, a submillimeter-accurate localization method is developed to identify fiducial markers more precisely for the registration of MRI and MPI volumes. With this method a IVOCT catheter is also tracked in 4D for bimodal imaging of IVOCT and MPI. Further, the method of Magnetic Particle Imaging and Magnetic Particle Navigation is used to navigate magnetic particles through a bifurcation within a vascular flow. Finally, the novel easy-axis aligned MPI contrast is used to determine the easy-axis orientation of samples.Publicationtype: Doctoral Thesis353 255 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Towards accurate modeling of the multidimensional magnetic particle imaging physicsThe image reconstruction problem of the tomographic imaging technique magnetic particle imaging (MPI) requires the solution of a linear inverse problem. One prerequisite for this task is that the imaging operator that describes the mapping between the tomographic image and the measured signal is accurately known. For 2D and 3D excitation patterns, it is common to measure the system matrix in a calibration procedure, that is both, very time consuming and adds noise to the operator. The need for measuring the system matrix is due to the lack of an accurate model that is capable of describing the nanoparticles’ magnetization behavior in the MPI setup. Within this work we exploit a physical model that is based on Néel rotation for large particle ensembles and we find model parameters that describe measured 2D MPI data with much higher precision than state of the art MPI models. With phantom experiments we show that the simulated system matrix can be used for image reconstruction and reduces artifacts due to model-mismatch considerably.Publicationtype: Journal ArticleScopus© Citations 34 412 343 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , 3D printed anatomical model of a rat for medical imaging(De Gruyter, 2019-09-18); ; ; ; For medical research, approximately 115 million animals are needed every year. Rodents are used to test possible applications and procedures for the diagnosis of anatomical and physiological diseases. However, working with living animals increases the complexity of an experiment. Accurate experimental planning is essential in order to fulfill the 3R rules (replace, reduce and refine). Especially in tracer-based imaging modalities, such as magnetic particle imaging (MPI), where only nanoparticles give a positive contrast, the anatomical structure of the rodent is not visible without co-registration with another imaging modality. This leads to problems in the experimental planning, as parameters, such as field of view, rodent position and tracer concentration, have to be determined without visual feedback. In this work, a 3D CAD rat model is presented, which can be used to improve the experiment planning and thus reduce the number of animals required. It was determined using an anatomy atlas and 3D printed with stereolithography. The resulting model contains the most important organs and vessels as hollow cavities. By filling these with appropriate tracer materials, the phantom can be used in different imaging modalities such as MPI, magnetic resonance imaging (MRI) or computed tomography (CT). In a first MPI measurement, the phantom was filled with superparamagnetic nanoparticles. Finally, a successful visualization of all organs and vessels of the phantom was possible. This enables the planning of the experiment and the optimization of experimental parameters for a region of interest, where certain organs in a living animal are localized.Publicationtype: Journal ArticleScopus© Citations 8 603 570 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Human-sized magnetic particle imaging for brain applications(Nature Publishing Group, 2019-04-26); ; ; ; Determining the brain perfusion is an important task for diagnosis of vascular diseases such as occlusions and intracerebral haemorrhage. Even after successful diagnosis, there is a high risk of restenosis or rebleeding such that patients need intense attention in the days after treatment. Within this work, we present a diagnostic tomographic imager that allows access to brain perfusion quantitatively in short intervals. The device is based on the magnetic particle imaging technology and is designed for human scale. It is highly sensitive and allows the detection of an iron concentration of 263 pmolFe ml-1, which is one of the lowest iron concentrations imaged by MPI so far. The imager is self-shielded and can be used in unshielded environments such as intensive care units. In combination with the low technical requirements this opens up a variety of medical applications and would allow monitoring of stroke on intensive care units.Publicationtype: Journal ArticleScopus© Citations 238 451 365 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Toward employing the full potential of magnetic particle imaging: Exploring visualization techniques and clinical use cases for real-time 3D vascular imagingMagnetic particle imaging (MPI) is a relatively young, radiation-free imaging modality that measures the interaction between superparamagnetic nanoparticles and magnetic fields. Compared to standard imaging modalities, a key feature of MPI is its ability to measure 3D volumes of relatively high spatial resolution in real-time, while still maintaining high sensitivity. Therefore, MPI is considered promising especially for vascular imaging and interventions. Yet, to fully take advantage of the unique MPI properties, real-time 4D imaging has to be combined with appropriate real-time 4D visualization and image analysis techniques. The current work aims at identification of respective clinical use cases and scenarios to illustrate the potential of MPI in the context of vascular imaging and interventions; the implementation and exploration of suitable visualization and image analysis techniques; and evaluation and comparison of the resulting image data to standard clinical imaging approaches. The study is based on three clinical use cases and associated anatomical sites: mechanical thrombectomy (anatomical structure: middle cerebral artery, segments M1 and M2); endovascular coiling (internal carotid artery aneurysm); and chemoembolization (proper hepatic artery). Implemented visualization and image analysis options are based on direct volume rendering and cover aspects like optimal view point and view angle selection and application of cut-away views. We illustrate that combining MPI imaging and 4D visualization helps to improve vascular image interpretation.Publicationtype: Conference Paper214