Drive field filter design for magnetic particle imaging (MPI) apparatus

Magnetic Particle Imaging (MPI) is an emergent imaging modality that can produce quantitative maps of injected superparamagnetic iron oxide nanoparticles (SPIONs) [1,4]. In MPI, the SPION magnetization is driven into saturation by an AC magnetic field at the drive frequency, f₀, generating harmonics, which are measured by Faraday detector coils. The large size of the SPION magnetization compared to nuclear spins suggests that functional neuroimaging with MPI (fMPI) will have a significant sensitivity benefit compared to fMRI. MPI requires a drive field at a single frequency, without harmonics, in order to have high contrast to noise ratio (CNR). Consequently, an MPI system should include a transmit filter to attenuate frequencies greater than f₀. In this paper, the design, construction, and characterization of a high power low-pass filter for the drive field is presented. The filter achieves an attenuation of 69.3 dB between the drive frequency, 25 kHz, and the 3^rd harmonic frequency, 75 kHz. The design of this filter fits into a larger experiment, in which MPI will be used to image CBV changes in the rat somatosensory cortex.