Development of a novel MR head coil integrated with PET detectors: Design and optimization of shield boxes

We are developing a new PET/MRI system based on our novel concept: an MR head coil integrated with PET detectors. To reduce electromagnetic interaction between the PET detectors and the MRI coil, the PET detectors are covered with conductive shield boxes. However, when the magnetic field around the shield box is changed by field gradient, eddy current is generated in the shield box, and that produces secondary magnetic field degenerating image quality. In this study, we quantitatively evaluated the secondary magnetic field induced by the eddy current. We created a map of the secondary magnetic field in the whole measuring system (ΔB0 map). The ΔB0 maps with and without shield boxes contrast were nearly the same. This suggests that the effect of the shield-box-inducing eddy current is smaller than that of the eddy current generated by the whole measurement system.