Design and development of an MR-compatible PET scanner for imaging small animals

An MR compatible PET system has been designed and is currently under construction. It will consist of four concentric rings of LSO crystals, each coupled to one of eight multi-channel photomultiplier tubes via 3.5 m optical fibres. The photomultiplier tubes may be located outside the main magnetic field of the MR scanner. A highly reproducible method has been established to optimise the amount of scintillation light that reaches the PM tubes, as this factor will heavily influence the scanner performance. Two small sections of the scanner, each containing 4 by 4 crystal arrays, demonstrated good flood position histograms with all sixteen channels clearly identifiable. The light loss through a fibre of length of 3.25 m was approximately 70%. The spatial resolution of the two arrays in coincidence was measured at 1.6 mm (FWHM). The temporal resolution of one array in coincidence with a single LSO crystal was measured to be 10.9 ns. A technique for improving sampling at the centre of the field of view within the scanner has also been investigated, whereby the concentric rings are offset with respect to one another. An offset of one quarter of the crystal width between layers results in significantly improved sampling. These results indicate that the scanner will be capable of carrying out the studies for which it has been designed.