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Item type:Publication, Access status: without files , On magnetic dipole-dipole interactions of nanoparticles in magnetic particle imagingMagnetic dipole-dipole (MDD) interactions between iron oxide nanoparticles can influence the sensitivity, image resolution and quantification of magnetic particle imaging (MPI). For the first time, the Landau-Lifshitz-Gilbert equation (LLG) for MDD interactions has been solved to investigate the effect of MDD interactions on the MPI spectrum. It was found that at concentrations above 39 mmol(Fe) l-1, MDD interactions significantly influence MPI spectra. This influence increases with increasing harmonics, which means first harmonics should be preferred for iron quantification. Since ≈1018 particles are neglected in the LLG compared to in an MPI experiment, the calculated limit below which MDD interactions can be neglected is only a bound. The true limit is therefore below the calculated limit of 39 mmol(Fe) l-1, because all other neglected particles also contribute to deviations in the MPI spectra via MDD interactions. Therefore, a quantum mechanical bound on the influence of MDD interactions is calculated, including up to 1015 particles. Analysis of the bound as a function of the particle number provides a valuable insight into the influence of the large number of particles neglected in numerical simulations. Both results are compared with concentrations in biomedical MPI experiments. We conclude that the standard approximation of an absence of MDD interactions in MPI experiments must be handled more carefully. Our method of incorporating MDD interactions into the LLG can be easily implemented as part of model-based reconstruction to increase the sensitivity, image resolution and quantitative tracer detection during MPI.Publicationtype: Journal Article140 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Geometry planning and image registration in magnetic particle imaging using bimodal fiducial markers(2016-06-01); ; ; ; Purpose: Magnetic particle imaging (MPI) is a quantitative imaging modality that allows the distribution of superparamagnetic nanoparticles to be visualized. Compared to other imaging techniques like x-ray radiography, computed tomography (CT), and magnetic resonance imaging (MRI), MPI only provides a signal from the administered tracer, but no additional morphological information, which complicates geometry planning and the interpretation of MP images. The purpose of the authors study was to develop bimodal fiducial markers that can be visualized by MPI and MRI in order to create MP-MR fusion images. Methods: A certain arrangement of three bimodal fiducial markers was developed and used in a combined MRI/MPI phantom and also during in vivo experiments in order to investigate its suitability for geometry planning and image fusion. An algorithm for automated marker extraction in both MR and MP images and rigid registration was established. Results: The developed bimodal fiducial markers can be visualized by MRI and MPI and allow for geometry planning as well as automated registration and fusion of MRMP images. Conclusions: To date, exact positioning of the object to be imaged within the field of view (FOV) and the assignment of reconstructed MPI signals to corresponding morphological regions has been difficult. The developed bimodal fiducial markers and the automated image registration algorithm help to overcome these difficulties.Publicationtype: Journal Article129 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Magnetic particle / magnetic resonance imaging: in-vitro MPI-guided real time catheter tracking and 4D angioplasty using a road map and blood pool tracer approach(Public Library of Science (PLoS), 2016-06-01); ; ; ; In-vitro evaluation of the feasibility of 4D real time tracking of endovascular devices and stenosis treatment with a magnetic particle imaging (MPI) / magnetic resonance imaging (MRI) road map approach and an MPI-guided approach using a blood pool tracer.Publicationtype: Journal Article455 461 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Increasing the sensitivity for stem cell monitoring in system-function based magnetic particle imaging(IOP Publishing, 2016-04-01); ; ; ; The use of superparamagnetic iron oxide nanoparticles (SPIONs) has provided new possibilities in biophysics and biomedical imaging technologies. The magnetization dynamics of SPIONs, which can be influenced by the environment, are of central interest. In this work, different biological SPION environments are used to investigate three different calibration methods for stem cell monitoring in magnetic particle imaging. It is shown that calibrating using SPIONs immobilized via agarose gel or intracellular uptake results in superior stem cell image quality compared to mobile SPIONs in saline. This superior image quality enables more sensitive localization and identification of a significantly smaller number of magnetically labeled stem cells. The results are important for cell tracking and monitoring of future SPION based therapies such as hyperthermia based cancer therapies, targeted drug delivery, or tissue regeneration approaches where it is crucial to image a sufficiently small number of SPIONs interacting with biological matter.Publicationtype: Journal Article164 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Sensitivity Enhancement in Magnetic Particle Imaging by Background Subtraction(2016-03); ; ; ; Biomedical applications such as cell tracking and angiography require the detection of low concentrations of superparamagnetic iron oxide nanoparticles (SPIOs) for imaging purposes. Magnetic particle imaging (MPI) is a new technology which enables the quantitative and time-resolved localization of SPIO distributions. However, the minimum concentration at which the SPIOs can be reconstructed with a suitable quality still remains to be investigated. In this work we examine the background signals in raw data that were measured without any SPIOs in the scanner tube. We show that a background subtraction in combination with a frequency cutoff for the dynamic part of the background signal lowers the detection limit for SPIOs in MPI up to a factor of ten. In-vivo mouse experiments show that for early time points from when the tracer enters the vena cava a reconstructed image of sufficient quality can only be obtained when a background subtraction is performed.Publicationtype: Journal Article173 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Geometrieplanung und Bildregistrierung mittels bimodaler Fiducial-Marker für Magnetic Particle Imaging(Springer, 2016-03); ; ; ; Publicationtype: Conference Paper282 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Joint reconstruction of non-overlapping magnetic particle imaging focus-field data(2015-04-21); ; ; The focus field is a key component to enable clinical applications in magnetic particle imaging (MPI). Due to physiological constraints, the method of choice is to place the focus of a small acquisition volume at various static positions in space and acquire the full field-of-view using a multi-station approach. In the first experiments, overlapping drive-field patches were used and boundary artifacts between drive-field patches were reduced using image processing. In this work we show that artifact-free reconstruction of non-overlapping focus-field data is feasible by using a joint reconstruction algorithm. This enables maximum scanning efficiency in multi-station focus-field experiments, which is key for reaching sufficiently short acquisition times to image the human heart.Publicationtype: Journal ArticleScopus© Citations 48 78