Design and construction of gradient coils for an MRI-guided small animal radiation platform

Small animal radiation experiments use a dedicated hardware platform to deliver radiation to small animals to support pre-clinical radiobiological studies. Image guidance is critical to achieve experiment accuracy. MR-based image guidance became recently available in human radiation therapy by integrating an MR scanner with a medical linear accelerator. Our group is developing a small animal MR-guidance system for pre-clinical radiation studies using a unique low-field unilateral magnet design. In this paper, we reported our design, construction, and characterization of split gradient coils for the MRI scanner. The coils were designed to have a 4 cm gap to allow the radiation beam to pass through for radiation experiments. We designed the coil patterns by solving an optimization problem. We constructed the coils by printing molds for the designed coil patterns using 3D printing technology and wiring the coils following the pattern. We measured parameters of the coils to characterize their performance. The coils achieved a linear magnetic field throughout a 4 cm spherical region of interest. The slew rates were 8640 and 1970 T/m⋅s, and the efficiencies were 1.2 and 0.21 mT/m⋅A for the Y-coil and X-coil, respectively. Preliminary imaging with the coils on our proposed system validates spatial encoding functions of the developed coils.