Gradient-based rotational drift and frequency encoding for high-resolution magnetic particle imaging

Abstract

Magnetic particles exhibit nonlinear rotational drift in rotating magnetic fields, which is dependent on the particle properties and external fields. The rotational drift frequency difference from the particles on an FFL in a gradient rotational excitation field may generate a free-induction decay signal and can be used as a phase encoding method for simultaneous high-resolution and large field-of-view MPI. We propose the use of gradient-based rotational drift to excite magnetic nanoparticles on an FFL. The different rotational drift frequencies from different FFL locations induce free induction decay and refocused echo signals. Magnetic particle concentrations on the FFL can be solved by using Fourier-transform-based reconstruction. The simulation was performed using in-house developed software based on the Interactive Data Language. IDL. The 2D Shepp-Logan phantom and the digital vessel phantom were used for an FFL-based raster scan and image reconstruction simulation. The correlation coefficient between the original and reconstructed images was used for image quality assessment. The dephasing signals and echos form a k-space for image reconstruction. Reconstructed images exhibited an increasing resolution from left to right with an increasing rotational drift frequency slope under a spatially linear excitation field. In the reconstructed brain TOF-MRA image with multi-angle gradient-based rotational excitation from filtered back-projection, the main branches and small vessels are visible with a high peak SNR. In conclusion, we propose the use of gradient-based rotational drift to excite magnetic nanoparticles for high-resolution MPI.