Relatively hydrophilic and/or big molecules have difficulty in crossing the BBB. This hurdle has kept many promising drug treatments on the sidelines because they cannot reach their target. The same applies for certain radiotracers in brain imaging. In order to overcome this problem Nanoparticles (NP) that target specific transport mechanisms in the BBB are in development. In order to evaluate the efficacy and safety of these particles, imaging technologies should be developed that can assess the mechanism of action at a molecular and cellular level. Two emerging brain imaging technologies may fill this need: Fluorescence Molecular Tomography ( FMT) and Multispectral Optoacoustic Tomography ( MSOT). In the meantime we can image the NP using PET, but a more detailed imaging technology is still lacking. This will not only be useful for solving the BBB but for any study that calls for a very high resolution.
Here is a paper discussing this topic-
Bhaskar S, et al. Multifunctional nanocarriers for diagnostics, drug delivery and targeted treatment across blood-brain barrier: perspectives on tracking and neuroimaging, Particle and Fibre Toxicology 2010, 7:3
Adolfo Cotter, MD