Assessment of shielding materials for the add-on PET at different magnetic field strengths of mri

We are developing a novel PET/MRI system. In this system, PET detectors are closely located to the MR RF-coil. To reduce the electromagnetic interaction between the PET detectors and the RF-coil, the PET detectors are covered with conductive shield boxes. However, when the magnetic field around the shield box is changed by MRI field gradient pulses, an eddy current is generated in the shield box. The eddy current produces the secondary magnetic field (ΔB
₀
), resulting in degraded MR image quality. The interference effect may depend on the static magnetic field strength of the MRI. In our previous work, we evaluated the signal-to-noise ratio and the eddy current for several shield materials with a 3 T clinical MRI system. The results showed that carbon fiber roving had high shielding performance and suppression capacity for the eddy current this paper, we evaluated performance of the carbon fiber roving in different static magnetic field strengths of the MRI. The results showed that carbon fiber roving had high shield performance regardless of the static magnetic field strength. From the experiment using the 3 T MRI, we clarified that the ΔB
₀
of carbon fiber roving was equivalent to ΔB
₀
of FRP. The slew rate of the gradient magnetic field of 0.3 T MRI is lower than that of the 3 T MRI, therefore, the eddy current and ΔB
₀
of the 0.3 T MRI are lower than those of the 3 T MRI. Thus, we judged that carbon fiber roving was valid as the shield material of shield boxes regardless of magnetic field strength of the MRI.