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 MPI. This study aimed to improve the magnetic field intensity of a birdcage-like coil to provide a shift field in 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 multi-turn 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 in the XOY plane. A 3D 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.