Mixing-Space Magnetic Particle Imaging

In this article, we propose a novel approach of mixing-space magnetic particle imaging (MPI) based on the combination of the spatial domain and frequency domain. For 2-D MPI, the superparamagnetic iron oxide nanoparticles (SPIONs) spectra are measured for frequency-domain reconstruction in the x-direction, whereas the SPION spectra in different field-free-point (FFP) positions are used for spatial-domain reconstruction in the y-direction. The system matrix is formulated with the SPION spectra in different x positions along the x-direction and different FFP positions along the y-direction, thus allowing to deblur the SPION image in both x- and y-directions. A 2-D MPI system is designed and built to generate a drive field in the x-direction and a shift field in the y-direction, as well as to measure the SPION spectra. Phantom experiments of two spots demonstrate that the proposed approach allows for spatial resolutions of 0.3 mm in the x-direction and 0.8 mm in the y-direction at 1.14 T/m. The SPION samples with different iron concentrations are used to assess the limit of detection (LOD), showing an LOD of$1.04~\mu $g (Fe)/mL (104 ng Fe weight) using Perimag SPIONs. The proposed mixing-space MPI approach significantly reduces both the hardware complexity and the processing time for system matrix measurement but still yields good spatial resolution.