Towards multimodal PET/MRI imaging with cyclotron-produced ^52/51Mn

Multimodality imaging is a diagnostic technique that combines morphological and functional information for improving the power of current imaging methods. PET or SPECT with CT are currently the most popular multimodal imaging technologies in this field while the combination of PET or SPECT with MRI (magnetic resonance imaging) is a newly-established technology. This multimodal technology usually involves the use of two different compounds, a contrast agent for MRI (i.e. Gadolinium-based molecules) and a radioactive tracer for PET/SPECT, generating a mismatch in the diagnostic information content. In this regard, we want to investigate the possibility and the effect of having a molecular fusion between PET and MRI by using a bimodal probe, a molecule able to be detected by both techniques. The same compound will act as a contrast and as a radioactive agent, preserving both the paramagnetic and nuclear characteristics. Manganese is the only transition element having paramagnetic properties suitable for MRI and two manganese isotopes, ⁵²Mn and ⁵¹Mn, positron emitters that could be employed as PET tracers. The scope of the METRICS project (METRICS: Multimodal pET/mRi Imaging with Cyclotron-produced ^52/51Mn iSotopes), funded by INFN (CSN5 2018–2020), aims to develop a perfect molecular matching between PET and MRI using paramagnetic and radioactive manganese isotopes to afford an unprecedented type of PET/MRI hybrid imaging and to develop the technology, target, and separation module to self-produce by cyclotron the ^51/52Mn. So far, natural chromium targets have been successfully produced and tested under a proton beam up to 50 μA (~ 1 kW) for thermomechanical tests, manganese paramagnetic complexes have been synthesized and characterized, while dosimetric studies and Cr/Mn radiochemical separation are currently under development. In this work we present the preliminary results of the METRICS project. The possible efficacy of having a real molecular fusion between PET and MRI by using a new bimodal probe, based on the use of manganese paramagnetic complexes, labelled with ^51/52Mn radionuclides will be underlined. (author)