A Multi-Slice Dual Layer MR-Compatible Animal PET System

Abstract

A multi-slice depth-of-interaction (DOI) MR-compatible PET system for imaging small animals such as mice or rats was developed and tested It employs DOI block detectors made of mixed lutetium silicates (MLSs), optical fibers, and multi-channel position sensitive photo-multiplier tubes (PSPMTs). The size of a single MLS was 2.5 mm times 3.5 mm times 3.5 mm and eight MLSs were combined to form a DOI block detector using the Anger principle and connected to four optical fibers with light guides. Thirty-two sets of block detectors were arranged in a 51 mm diameter circular ring. The scintillation light signals from the DOI detectors are read from the side of the detector ring. The configuration makes the diameter of the detector ring small and easy to use in the small imaging area of the MRI. Position histograms showed good separation for all block detectors. The timing resolution was 6 ns FWHM. The measured transaxial spatial resolution was 2.8 mm FWHM at the center of the image and the axial resolution was 3 mm FWHM. Sensitivity was around 0.23% at the center of the axial field of view (FOV). Simultaneous imaging of PET and MRI was also tested using a 0.15 T permanent magnet system with a 30-mm FOV. The detector part of the PET system was set inside the gradient coil of the MRI system and the RF coil was positioned inside the FOV of the PET system. No difference was found in the PET images among outside MRI, inside MRI without gradient and RF, and inside MRI with the gradient and the RF sequences. Also there is no noticeable change of the MRI images with and without the detector ring of the PET system. We also successfully obtained simultaneously measured rat brain with the PET and MRI. These results indicate that the developed MR-compatible PET system can be used for simultaneous measurements with an MRI system.