Multi-harmonic system matrix fusion for field-free-point gridded magnetic particle imaging

In this study, we propose an approach for field-free-point (FFP) gridded magnetic particle imaging (MPI) by fusing the 3rd, 5th, 7th and 9th harmonics of superparamagnetic iron oxide nanoparticles (SPIONs) to visualize the spatial distribution of the SPIONs. The full width at half maximum (FWHM) of the point spread function (PSF) and the signal strength of each harmonic are analyzed to investigate their effect on the performance of MPI. Afterwards, the system matrices of all harmonics, derived from their respective PSFs, are fused to deduce the forward imaging model. Numerical simulations are performed to demonstrate the feasibility of the proposed method for MPI. We compare the proposed approach with single-harmonic-based narrowband MPI regarding spatial resolution and signal-to-artifact ratio (SAR). In addition, phantom experiments are performed with a custom-built MPI system. Experimental results demonstrate that the proposed method achieves a good trade-off regarding the spatial resolution and SNR by taking the advantages of high spatial resolution from higher harmonics and high SNR from lower harmonics.