Image reconstruction based on FWHM-Energy Joint Weighting for Magnetic Particle Imaging

Abstract Objective: Magnetic particle imaging (MPI) enables high-sensitivity quantitative imaging by detecting the nonlinear magnetization response of superparamagnetic nanoparticles. FFPgridded MPI has been developed to reduce system complexity, and its multi-harmonic extension exploits harmonic-dependent information to balance spatial resolution and SNR. However, an appropriate weighting strategy is required to utilize complementary information across harmonics. We propose an image reconstruction method based on full width at half maximum (FWHM)-energy joint weighting, which combines PSF-derived FWHM with either L2-norm harmonic energy or noise energy to achieve a favorable trade-off between spatial resolution enhancement and reconstruction stability. Approach: In the FFP-gridded multi-harmonic fusion framework, the 3 rd , 5 th , 7 th , and 9 th harmonic components are jointly used for image reconstruction. Since different harmonics exhibit distinct characteristics in signal intensity, noise level, and spatial resolution, optimizing their weights is essential for improving reconstruction quality. Traditional weighting strategies based on amplitude, signal energy, and noise characteristics were implemented as comparison methods. On this basis, two FWHM-energy joint weighting strategies were developed: L2norm energy-FWHM weighting for balancing resolution improvement and artifact suppression, and noise-energy-FWHM weighting for enhancing the spatial resolution of noise-suppressed reconstruction. Main Results: The proposed methods were validated through numerical simulations and phantom experiments under different noise conditions and phantoms. The results demonstrate that the FWHM-energy joint weighting strategies improved reconstruction quality compared with traditional weighting methods. By incorporating spatial resolution information into harmonic weighting, the proposed methods achieved a more favorable balance among spatial resolution, artifact suppression, and reconstruction stability. Significance: The proposed method introduces FWHM-energy joint weighting strategies for multi-harmonic MPI reconstruction, enabling spatial resolution enhancement while preserving reconstruction stability. Future work will focus on extending this framework to adaptive weighting schemes and more complex scenarios, thereby improving the applicability of multiharmonic MPI reconstruction.