There are several different ligands (binding molecules) which can be used to visualise TSPO in PET imaging and this study uses one called PBR28. The problem with this ligand is that people commonly carry mutations which affect the binding affinity of PBR28, making them a low, moderate, or high affinity binder. This study did test for these mutations and excluded the low affinity binders, but did not then assess the data with regards to medium and high affinity binders. Could this be a problem? We're not sure yet, but again, this is something we're looking in to.
So, TSPO is a protein which could be very useful, but there are a lot of questions still to answer...