Fig. 2.

Combining PET and optical imaging as a tool for monitoring in vivo biodistribution of the liposome shell and core; PET tracks the shell while the optical probe tracks the aqueous core. 2a) In vivo optical efficiency resulting from injection of a serial dilution of liposomes ranging from 45 to 180 μg lipid and 0.15 to 0.6 nMols AF-750 verifies the linearity of in vivo fluorescence efficiency as a function of fluorophore concentration in the blood pool. 2b) Blood pool radioisotope % ID/cc, using an F-18 labeled lipid as a PET tracer, and optical efficiency vs time. Formulation I shows similar blood pool kinetics when monitoring the shell and core through both PET and optical methods, respectively. However, blood pool fluorescence of formulation III decreases as compared with radioisotope concentration, presumably through the “leaky” mechanism described in figure 1a. 2c) Tumor radioisotope % ID/cc, using a Cu-64 labeled lipid as a PET tracer of the shell, and optical efficiency of the vehicle core vs time. PET and optical probes of tumor accumulation show similar kinetics for each formulation. PET data in 2c also used within [45]. 2d) Bladder accumulation of the F-18 synthesized lipid as a PET tracer and AF-750 as an optical probe at the time of injection, after 6 min and 1 hour. 2e) Biodistribution of PET probes at 6 and 48 hours after injection using F-18 and Cu-64 labeled lipids as PET tracers, respectively (tumor accumulation not assessed at the 6-hour time point).