A sensitive, stable, continuously rotating FFL MPI system for functional imaging of the rat brain.

Magnetic particle imaging noninvasively maps the distribution of superparamagnetic iron oxide nanoparticles with high sensitivity. Since the particles are confined to the blood pool within the brain, it may be well-suited for cerebral blood volume (CBV)-based functional neuroimaging with MPI (fMPI). Here, we present a magnetic particle imaging system designed to detect the CBV modulation at the hemodynamic timescale (~5 sec) in rodents. It has the capacity to record sufficiently fast image time-series for several hours continuously. The time-series imaging was achieved with an optimized drive coil that maintains ~0.01% per minute current magnitude stability. An electrical slip ring and rotary union for cooling water allows continuous mechanical rotation of the 2.83 T/m Field-Free Line (FFL) permanent magnets and shift coils. The system achieves a 6.7 ng Fe detection limit (SNR = 5) in a single 5 sec image in the time-series, a spatial resolution of 3.0 mm in a 3 cm diameter field of view. The designs have been made open-source to enable replication of this device.