Presentation of test measurements with a commercial small animal PET/MR imaging system

Objectives We have developed a compact, sequential PET/MR system for rodents. We built the PET/MR on our existing crystal-based PET detector technology and a special, permanent magnet MR subsystem minimizing external magnetic field effects. We present some first, important performance measurements of the system with PET and MR working in close proximity.

Methods The Mediso nanoScan® PET/MR imaging system has 12 PET detector modules of 81x39 LYSO crystals (1.12x1.12x13mm), tightly packed (pitch 1.17 mm, PF 92%) coupled to two 256-channel PS-PMT’s. Modular PET ring design was favored to avoid inhomogeneities in the centre of the FOV. PET is aligned axially in front of the MR component that has 1 Tesla field strength with 90 mm diameter and 60 mm high barrel FOV, specified with 100 micron areal pixel resolution. Animal is moved from the PET ring bore to the MR subsystem bore with a common animal bed as in a PET/CT. The center of the PET FOV is close to the MR magnet bore opening (distance: 6.425 cm). We have measured the PET ring performance with the MR system working using a 22Na point source and a 0.8-1.5 mm rods Micro-Derenzo phantom filled with 18F-FDG. We also present signal/noise ratio (S/N) of the MR subsystem before and after integration using a 35 mm diameter mouse coil.

Results PET resolution in center FOV (2D-OSEM reconstruction) ranged from 0.97 to 1.34 mm, sensitivity in the center was 7.40%. The MR subsystem S/N ratio was 714/mm3 before the integration. With working PET electronics and PET detector within the combined system MR S/N ratio was 664/mm3. Original MR subsystem specification is >500/mm3.

Conclusions The PET/MR imaging system has been found to fulfil the original PET and MR specifications. Cross-talk effects are well tolerable. The Mediso PET/MR system presented here is a prompt, viable and commercially unique solution providing high PET resolution and effective, flexible MR imaging in the same animal and imaging session.

Research Support Mediso Ltd