Studies have shown that the approach enhances contrast and improves the ability to delineate boundaries . Using this approach, simultaneous PET–MRI would not only provide co-registered PET and MR images but also enable the improvement of PET spatial resolution and contrast. Recent efforts have combined the technique with anatomical probabilistic atlases to yield PVE-corrected functional volumes of great accuracy, and the results have begun to be deployed in clinical studies . The topics discussed above in 2 and 3 can also assist in improving the accuracy of quantitative PET by reducing motion error (and the associated increase in noise) and improving PET
reconstruction via anatomical priors. MR could be used for detecting and tracking motion due to respiration, the cardiac cycle and gross Selleckchem Sirolimus patient movement during the dynamic PET acquisition. Of course, by improving the PET reconstruction using the anatomical priors available from the MRI data, the PVE is reduced. A fundamental question surrounding
the potential future use and clinical application of dual PET–MRI contrast agents Selleckchem PD98059 is the vast difference in inherent sensitivities of the two techniques; PET studies require picomolar concentrations of the tracer, while the typical gadolinium MRI contrast agents require millimolar concentrations. However, these issues have not deterred the field from developing agents that can be detected simultaneously by each modality. To partially span the sensitivity gap, agents have been developed by tethering ADP ribosylation factor positron emitters to dextran-coated superparamagnetic iron oxide (SPIO) nanoparticles which require only micromolar concentrations to achieve reasonable MR contrast. We now briefly highlight some recent illustrative examples of this approach. Torres et al. attached 64Cu to a bisphosphonate (bp) group that binds to the dextran surface  of an SPIO. The copper is chelated within dithiocarbamate
(dtc) to form [64Cu(dtcbp)2] which has great affinity for the SPIO’s dextran. Upon in vivo (sequential) PET–MRI imaging, this construct showed retention only in the popliteal and iliac lymph nodes. Another example of a 64Cu-MION probe was developed by Glaus et al. who coated an SPIO with polyethylene glycol (PEG) phospholipids. DOTA (1,4,7,10-tetraazacyclo-dodecane-1,4,7,10-tetraacetic acid) was used to chelate 64Cu and then conjugated to the PEG . The authors performed in vivo pharmacokinetic analysis with their construct in a murine model via microPET/CT and organ biodistribution studies. They concluded that the ability of the agent to have high initial blood retention with only moderate liver uptake makes it a potentially attractive contrast agent. They also noted that, in general, linking the PET agent to the nanoparticle provides improved circulation half-life . Noting that the lymphatic system is a common route of metastases for cancer, Choi et al.