Phase-Lag-Based MPS/MPI Dual-Mode Precise In Vivo Temperature Imaging Technique

Magnetic Particle Imaging (MPI) enables noninvasive temperature imaging without depth limitations. However, due to the lack of effective calibration strategies that can simultaneously address issues such as calibration infeasibility and environmental mismatch, its practical in vivo application remains challenging. In this work, we propose a novel in vivo temperature imaging method based on a dual-mode magnetic particle spectroscopy/magnetic particle imaging (MPS/MPI) system. First, MPS is employed to capture the differences in harmonic phase responses of magnetic nanoparticles (MNPs) under in vivo and in vitro conditions, thereby enabling the construction of calibration functions that are consistent with the in vivo environment. Second, an MLP based calibration strategy is proposed, which accounts for non-ideal deviations from the approximately linear temperature-phase relationship and integrates multi-parameter information into a unified network, thereby enabling accurate and stable temperature mapping. Comprehensive simulation, in vitro, and in vivo experiments demonstrate that, compared with conventional phantom-based temperature mapping methods, the proposed method reduces the in vivo temperature reconstruction error by approximately 17.24% and achieves an average absolute temperature error below $1.257~^{\circ } $ C. These results verify the feasibility of accurate in vivo temperature imaging using MPI and provide essential technical support for temperature-sensitive applications, including magnetic hyperthermia.