Relaxation spectral analysis in multi-contrast vascular magnetic particle imaging

Abstract

Magnetic nanoparticles (MNPs) are used as tracers for vascular imaging without ionizing radiation. There is a high demand for the simultaneous detection of multiple particle states in multi-contrast magnetic particle imaging (MPI). In this study, the Néel and Brownian relaxation times were decoupled and measured separately to characterize different particle states using interventional vascular imaging as an example. The relaxation spectrum was generated via inverse Laplace transform (ILT)-based spectral analysis of the decay signals in the field-flat phase of pulsed excitation. The Néel and Brownian relaxation components were investigated through experiments involving the excitation of synomag-D samples using a trapezoidal-waveform relaxometer. The Brownian relaxation time was identified in the relaxation spectra due to a linear increase with increasing viscosity and disappeared at high gelatin concentrations. The sensitivity of viscosity prediction of the decoupled relaxation times under different excitation-field amplitudes was evaluated. Spectral imaging of a digital vascular phantom was simulated by combining a field-free point with homogeneous pulsed excitation. The plaque region with bounded MNPs and the catheter region with solidified MNPs were simultaneously differentiated from the vessel region in the Brownian relaxation time map. We demonstrated the quantitative assessment of the Néel and Brownian relaxation times through ILT-based spectral analysis in pulsed excitation, highlighting their potential for use in multi-contrast vascular MPI.