An Optimized Variable Number of Windings Approach to Design a Birdcage-Like Shift Coil for MPI System

At present, the rotating dipole Halbach magnets was used to generate a shift field for the quadrupole Halbach magnets and the magnetic field intensity generated by birdcage coil in MRI is too small to be used as a shift field in magnetic-particle imaging (MPI). This study aimed to improve the magnetic field intensity of a birdcage-like coil to provide a shift field in a low-gradient (0.2 T/m) MPI system. A variable number of windings approach is optimized from the single-layer design of RF coils suitable for MRI to a multilayer design of shift coils for MPI, thus extending the application of birdcage-like coils as shift coils for MPI systems for the first time. The number of turns on different winding layer or radii was solved and multiturn litz wires were utilized to replace single-layer copper sheet or Litz wire. The quadrature mode wound was further used to turn the shift field to rotate, thereby moving field-free-point (FFP) in the XOY plane. A 3-D printing bracket with adjustable length was utilized to fix the routing of a practical coil and increase the availability of internal space for the shift coil without affecting its performance. A birdcage-like shift coil was designed and constructed, and the simulation results and measurement results are presented.