Evaluation of semi-monolithic scintillators with integrated RF shielding material for a higher integration of PET/MRI systems

TL;DR

This study evaluates semi-monolithic scintillators with integrated RF shielding for PET/MRI systems, demonstrating effective RF shielding and maintained PET performance, enabling higher integration of the two modalities.

Contribution

It introduces a novel shared-volume concept with integrated RF shielding in scintillators, improving PET/MRI integration without compromising performance.

Findings

Highest shielding effectiveness of 31 dB with 12 mm height prototype.

Energy resolution of 10.6% achieved with ESR scintillators.

Timing resolution around 280 ps maintained with shielding.

Abstract

The integration of PET into MRI to form a hybrid system requires often compromises for both subsystems. For example, the integration might come at the cost of a reduced PET detector height or a reduced MRI examination volume diameter. Here, we propose a so-called shared-volume concept to use the volume required for both subsystems more efficiently, in which the MR transparency of the scintillator is exploited by integrating the RF shielding into the scintillator of the PET detector. Semi-monolithic scintillator prototypes (PVC slabs) of 7 mm and 12 mm height with integrated copper foil between every and every other slab, respectively, were investigated to evaluate the shielding effectiveness (SE). The SE was measured with probes on a test bench system. In addition, the PET detector performance was evaluated by determining the positioning using gradient tree boosting, energy and timing resolution using digital SiPM arrays (DPC3200, PDPC) in three LYSO scintillator configurations: ESR separation (Slab$\mathrm{_{ESR}}$), ESR with copper foil in between (Slab$\mathrm{_{ESR+Cu}}$), and purely copper foil separation (Slab$\mathrm{_{Cu}}$). The prototype with shielding between each slab and 12 mm height showed the highest SE with 31 dB (mean) in combination with a supporting frame. While Slab$\mathrm{_{Cu}}$ was best for positioning, followed by Slab$\mathrm{_{ESR}}$ and Slab$\mathrm{_{ESR+Cu}}$, the Slab$\mathrm{_{ESR}}$ had the best energy resolution (10.6 %), followed by Slab$\mathrm{_{ESR+Cu}}$ (11.2 %) and Slab$\mathrm{_{Cu}}$ (12.6 %). For the timing resolution, Slab$\mathrm{_{ESR}}$ and Slab$\mathrm{_{Cu}}$ achieved 279 ps and 288 ps, respectively. Slab$\mathrm{_{ESR+Cu}}$ performed worst (293 ps). The scintillator-based RF shielding shows good RF shielding with similar PET performance, demonstrating the potential for more effective integration of PET detectors into MRI systems.