Development of a system for magnetic particle imaging using neodymium magnets and gradiometer

We developed a system for magnetic particle imaging (MPI) using two opposing neodymium magnets for generating a magnetic-field-free line (FFL) and a gradiometer coil for receiving signals generated by magnetic nanoparticles (MNPs). The projection data were acquired by rotating and translating both a phantom and a gradiometer coil simultaneously, and transverse images were reconstructed using the filtered backprojection (FBP) method and maximum likelihood-expectation maximization (ML-EM) algorithm. The gradiometer coil was superior to a simple solenoid coil in terms of the linearity between the signal intensity and concentration of MNPs and of the robustness against feedthrough interference. The image quality was improved using the ML-EM algorithm compared with using the FBP method; in particular, the number of streak artifacts was reduced. Our preliminary results suggest that our system is useful for realizing MPI with an FFL-encoding scheme and that the ML-EM algorithm is useful for improving the image quality of MPI.