Browsing by Subject "Field free line"

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A novel hybrid magnetic particle imaging and low-field magnetic resonance imaging scanner
(2024-08) Karaca, Sefa
Magnetic particle imaging (MPI) is an emerging medical imaging modality, in which the spatial distribution of the magnetic nanoparticles (MNPs) are imaged using their non-linear magnetization curve. Since biological tissues do not exhibit such magnetic behavior, MNPs serve as the sole source of the MPI signal, making it a promising in vivo imaging modality with high contrast and sensitivity. However, anatomical information is also essential for many applications. To address this issue, MPI can be combined with other imaging modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI), using standalone or hybrid systems. It is particularly advantageous to combine MPI with MRI, given that they are both non-ionizing imaging modalities. Moreover, since both MPI and MRI utilize magnetic fields, a hybrid system that integrates these modalities can potentially reduce costs via shared utilization of hardware. This thesis introduces a novel preclinical-size hybrid MPI and low-field (LF) MRI scanner. The proposed system features an MPI mode with a field free line (FFL) topology and a selection field gradient of 0.25 T/m, alongside a LF-MRI mode with a B0 field strength of 50 mT. The primary advantage of this hybrid system lies in the interchangeable use of coil groups between MPI and LF-MRI modes, facilitating the generation of a multimodal image that features high sensitivity and contrast imaging of MNP distribution by MPI, alongside anatomical information from LF-MRI. Additionally, the coil configuration of this hybrid system features an open-sided design, with the exception of the Tx/Rx coil of MRI, which utilizes a solenoid design for experimental studies. This coil can be substituted with a surface coil, facilitating the development of an open-sided hybrid system. First, the feasibility of multimodal imaging with the proposed hybrid scanner is evaluated by characterizing the magnetic fields in the system. Next, the effects of system-induced deviations on image quality are investigated via an in-house MRI simulator. The experimental imaging results demonstrate that the proposed preclinical-size hybrid MPI and LF-MRI scanner can successfully perform multimodal imaging.
Open Access
Image reconstruction for Magnetic Particle Imaging using an Augmented Lagrangian Method
(IEEE, 2017) Ilbey S.; Top C.B.; Çukur, Tolga; Sarıtaş, Emine Ülkü; Guven H.E.
Magnetic particle imaging (MPI) is a relatively new imaging modality that images the spatial distribution of superparamagnetic iron oxide nanoparticles administered to the body. In this study, we use a new method based on Alternating Direction Method of Multipliers (a subset of Augmented Lagrangian Methods, ADMM) with total variation and l1 norm minimization, to reconstruct MPI images. We demonstrate this method on data simulated for a field free line MPI system, and compare its performance against the conventional Algebraic Reconstruction Technique. The ADMM improves image quality as indicated by a higher structural similarity, for low signal-to-noise ratio datasets, and it significantly reduces computation time. © 2017 IEEE.
Open Access
Tomographic field free line magnetic particle imaging with an open-sided scanner configuration
(IEEE, 2020) Top, C. B.; Güngör, Alper
Superparamagnetic iron oxide nanoparticles (SPIONs) have a high potential for use in clinical diagnostic and therapeutic applications. In vivo distribution of SPIONs can be imaged with the Magnetic Particle Imaging (MPI) method, which uses an inhomogeneous magnetic field with a field free region (FFR). The spatial distribution of the SPIONs are obtained by scanning the FFR inside the field of view (FOV) and sensing SPION related magnetic field disturbance. MPI magnets can be configured to generate a field free point (FFP), or a field free line (FFL) to scan the FOV. FFL scanners provide more sensitivity, and are also more suitable for scanning large regions compared to FFP scanners. Interventional procedures will benefit greatlyfrom FFL based open magnet configurations. Here, we present the first open-sided MPI system that can electronically scan the FOV with an FFL to generate tomographic MPI images. Magnetic field measurements show that FFL can be rotated electronically in the horizontal plane and translated in three dimensions to generate 3D MPI images. Using the developed scanner, we obtained 2D images of dot and cylinder phantoms with varying iron concentrations between 11 μg/ml and 770 μg/ml. We used a measurement based system matrix image reconstruction method that minimizes 11-norm and total variation in the images. Furthermore, we present 2D imaging results of two 4 mm-diameter vessel phantoms with 0% and 75% stenosis. The experiments show high quality imaging results with a resolution down to 2.5 mm for a relatively low gradient field of 0.6 T/m.