  Magnetic particle imaging (MPI) is an in-vivo imaging method to detect
magnetic nanoparticles for blood vessel imaging and molecular target imaging.
Compared with conventional molecular imaging devices (such as nuclear medicine
imaging PET and SPECT), magnetic nanoparticles have longer storage periods than
radionuclides without ionizing radiation. MPI has higher detection sensitivity
compared with MRI. To accurately locate molecular probes in living organisms,
high-resolution images are needed to meet the requirements of precision
medicine. The spatial resolution of the latest domestic and international MPI
equipment is 1-6 mm and has not yet met the requirements of medical imaging
detection. We previously studied the spatial encoding technology based on
pulsed square wave stimulation, which significantly improved the image
resolution along the field free line (FFL) direction. This study proposes an
innovative idea of high-resolution MPI based on stimulated emission depletion
(STED) of magnetic nanoparticle signals. The stimulated emission was
implemented by using cosine stimulation on FFL-based MPI scanner systems. The
STED signal was generated by adding an offset magnetic field parallel to the
FFL, which may form a donut-shaped focal spot or a regular Gaussian focal spot
depending on the offset field strength. Focal spot modulation techniques and
deconvolution algorithms were developed to improve image resolution.
