A novel hybrid magnetic particle imaging and low-field magnetic resonance imaging scanner

Abstract

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.