Phase-based stimulated emission depletion (pSTED) magnetic particle imaging

TL;DR

This paper introduces a phase-based STED-inspired method in magnetic particle imaging to achieve super-resolution imaging by creating a donut-shaped focal spot, surpassing traditional resolution limits.

Contribution

It proposes a novel phase-based approach using STED principles to enhance MPI resolution beyond the Langevin magnetization barrier.

Findings

Achieved up to 4 times reduction in focal spot size.

Demonstrated super-resolution imaging in human brain MPI scanner.

Enabled super-sensitivity through deconvolution and filtering techniques.

Abstract

Magnetic particle imaging (MPI) is an in vivo method to detect magnetic nanoparticles for cell tracking, vascular imaging, and molecular target imaging without ionizing radiation. Current magnetic particle imaging is accomplished by forming an field-free line (FFL) through a gradient selection field. By translating and rotating FFL under excitation and drive fields, the harmonic complex signal of a point source forms a Lorentzian-shape point spread function on the plane perpendicular to FFL. The Lorentzian PSF has a finite size and limited resolution due to the non-sharp Langevin function and weak selection field. This study proposes a donut-shaped focal spot by borrowing the stimulated emission depletion (STED) fluorescence microscopy principle. The influence of the gradient selection field on the relaxation time of magnetic particles determines the nonlinear phase shift of the harmonic complex signals, resulting in the formation of a donut-shaped focal spot. By subtracting the donut-shaped focal spot from the Lorentzian focal spot, the STED focal spot size was reduced by up to 4 times beyond the Langevin magnetization resolution barrier. In human brain FFL-based MPI scanner, the donut-shaped focal spot can be used to reconstruct images with super-resolution and super-sensitivity through the deconvoution of the STED focal spot and filtered backprojection algorithm.