A novel optically transparent RF shielding for fully integrated PET/MRI systems

Abstract

Preclinical imaging benefits from simultaneous acquisition of high-resolution anatomical and molecular data. Additionally, PET/MRI systems can provide functional PET and functional MRI data. To optimize PET sensitivity, we propose a system design that fully integrates the MRI coil into the PET system. This allows positioning the scintillators near the object but requires an optimized design of the MRI coil and PET detector. It further requires a new approach in realizing the radiofrequency (RF) shielding. Thus, we propose the use of an optically transparent RF shielding material between the PET scintillator and the light sensor, suppressing the interference between both systems. We evaluated two conductive foils (ITO, 9900) and a wire mesh. The PET performance was tested on a dual-layer scintillator consisting of 12 × 12 LSO matrices, shifted by half a pitch. The pixel size was 0.9 × 0.9 mm; the lengths were 10.0 mm and 5.0 mm, respectively. For a light sensor, we used a 4 × 4 SiPM array. The RF attenuation was measured from 320 kHz to 420 MHz using two pick-up coils. MRI-compatibility and shielding effect of the materials were evaluated with an MRI system. The average FWHM energy resolution at 511 keV of all 144 crystals of the layer next to the SiPM was deteriorated from 15.73 ± 0.24% to 16.32 ± 0.13%, 16.60 ± 0.25%, and 19.16 ± 0.21% by the ITO foil, 9900 foil, mesh material, respectively. The average peak-to-valley ratio of the PET detector changed from 5.77 ± 0.29 to 4.50 ± 0.39, 4.78 ± 0.48, 3.62 ± 0.16, respectively. The ITO, 9900, mesh attenuated the scintillation light by 11.3 ± 1.6%, 11.0 ± 1.8%, 54.3 ± 0.4%, respectively. To attenuate the RF from 20 MHz to 200 MHz, mesh performed better than copper. The results show that an RF shielding material that is sufficiently transparent for scintillation light and is MRI compatible can be obtained. This result enables the development of a fully integrated PET detector and MRI coil assembly.

Design and performance simulation studies of a breast PET insert integrable into a clinical whole-body PET/MRI scanner

“…Within this work the MRI compatibility was not investigated as this is highly dependent on the actual hardware. In general, it is possible to achieve mutual MRI compatibility by carefully designing RF shielding, choice of materials, filter and PCB layout (Kolb et al 2012, Nishikido et al 2017, Gonzalez et al 2019, Parl et al 2017, Disselhorst et al 2022.…”

Dual layer doI detector modules for a dedicated mouse brain PET/MRI

“…However, all essential components of the prototype setup such as scintillators, SiPMs, and amplifiers are available in non-magnetic versions. Furthermore, a possible shielding concept has been described by our laboratory (Parl et al 2017). To achieve a very compact PET/MRI system, we propose to use an RF shielding material between the scintillators and the light sensor.…”

Investigation of Faraday cage materials with low eddy current and high RF shielding effectiveness for PET/MRI applications

“…However, the very thin thickness also makes the manufacturing process more challenging for a stable performance. Mesh materials, such as stainless steel mesh and phosphor bronze mesh (Parl et al 2017, Yin et al 2021, have also been studied and are considered good candidates for MRI shielding in different applications. However, challenges such as seam filling and manufacturing difficulties exist with mesh shielding.…”