High-Resolution Enlarged Open-Bore Narrowband Magnetic Particle Imaging Based on Double-Layer Linear Scanning Structure

We developed a novel high-resolution open-bore narrowband magnetic particle imaging (MPI) system for big animal and future clinical usage. Optimized strength and direction of excitation field was invested for enlarged field of view (FOV), and a 4 T/m gradient field and its linear scanning trajectory were formed by 16 square coils without coupling to excitation, forming a maximum $120\times120$ mm open bore FOV. Furthermore, a new differential pickup structure consisted of multi Helmholtz excitation and pickup coils away from the FOV was proposed in order to suppress the system noises, which was very important for the limited coil setting space in open-bore MPI. The new differential structure contributed significantly to improve the signal-to-noise ratio (SNR) as high as about 100 dB without loss of harmonic signals. Several homemade resonant circuits, filters, and lock-in amplifier were used to constitute the high-precision signal acquisition system. Experimental results showed that the detection limit of the system was 1 ug Fe of Resovist sample with a spatial resolution of 1 mm after reconstruction, satisfying many clinical needs, such as drug delivery and bedside monitoring.