High-resolution MPI with spatially resolved measurement on field free lines

Abstract

In magnetic particle imaging (MPI), 1D projected signals can be collected by exciting magnetic particles on a field free line (FFL) with a homogeneous excitation field. The movements and rotations of FFL with projection reconstructions generate 2D and 3D images of magnetic nanoparticles. The image resolution is heavily relying on the wideness of FFL, which is limited by the currently available maximal gradient strength. We proposed an additional gradient field with the same direction as the FFL for pulsed excitation and 1D spatial encoding. The spatial encoding steps include different gradient excitation profiles along with the FFL. System matrix for 1D image reconstruction is based on the relaxation-induced decay signal during the flat portion of pulsed square-wave excitation. For larger magnetic particles, our simulation shows that the pulsed excitation field with a greater flat portion generates a 1D bar phantom image with higher correlation and higher spatial resolution. With parallel FFL movements, high-resolution 2D images of human brain-sized Shepp-Logan phantom and clinical transverse MRA datasets are reconstructed by spatially resolved measurement of magnetic nanoparticles on FFLs.