Integrated PET/MRI in preclinical studies State of the art

Abstract

International audienceThe exquisite tissue contrast of magnetic resonance imaging (MRI), the absence of ionising radiation and the opportunity to obtain new molecular and functional data have strengthened the enthusiasm for coupling MRI rather than computed tomography (CT) to positron emission tomography (PET). When reviewing the current literature one might be surprised by the almost unlimited diversity of what is placed under the name of PET/MRI in the articles. The magnetic field is varying from 0.3 Tesla (T) to 9.4 T, the size of the bore varies also from the wide bore of clinical scanners to volumes limited to a few tens of mL. Many preclinical studies are performed using separate PET and MRI scanners. Sometimes PET and the magnet are in line or sequential. More rarely, fully integrated PET/MRI scanners are used. In that case, mutual interference between PET and MRI has required innovative designs. Initially, the conventional photomultipliers had been installed outside the magnet using long optical fibres. They have now been replaced by avalanche photodiodes (APD), and in the near future silicon photomultipliers (SiPM) could provide an alternative. Tumours and neurological and cardiovascular disorders have been the most studied conditions. Many issues remain to be resolved such as image registration, attenuation correction and animal monitoring. Friendly consoles integrating the control of both imaging modalities also need to be developed