VIEWS: 22 PAGES: 13 CATEGORY: Medicine POSTED ON: 5/30/2010
Favorable characteristics include, high specific activity of the label (to avoid drug toxicity and preserve tracer characteristics); high site selectivity and specificity; appropriate binding affinity; suitable hydro/lipophilicity and size (which govern transport across barriers); suitable metabolism (metabolites are likely to carry the label but exhibit altered specificity); low immediate excretion (renal, hepatic) or sequestration (drug resistance transporters, phagocytes); low non-specific binding (as the background signal reduces contrast); and, the ability to achieve high local concentrations.11-15 Limitations of the use of injectable molecular imaging agents of different modalities can be explained to a great extent by their pharmacological properties. [...] ultrasound contrast agents (in the form of microbubbles) and magnetic resonance imaging (MRI) iron nanoparticles are relatively bulky, and are restricted by body membranes such as the vascular endothelium, the blood-brain barrier or the cell membrane; they are restricted much more than low-molecular-weight agents.16-25 Radionuclide-based labeling techniques, on the other hand, provide the ability of replacing atoms of biological molecules with their radioisotopes, resulting in radiolabeled injectable agents that ideally are chemically identical (same size, chemistry and charge) to their unlabeled state.
Molecular imaging: Techniques and current clinical applications David Bonekamp, MD, PhD, Dima A. Hammoud, MD, and Martin G. Pomper, MD, PhD T he Task Force of the Society of Nuclear Medicine (SNM) Mol- ecular Imaging Center of Excel- lence (MICoE) defines molecular imaging as the “visualization, charac- terization and measurement of biologi- cal processes at the molecular and cellular levels in humans and other liv- ing systems.”1 In the context of translation into clinical practice, molecular imaging would perhaps better be known as “molecular diagnostic imaging,” to distinguish it from “classical diagnos- tic imaging.” Unlike the latter, molecu- lar imaging goes beyond structural assessment, and probes disease-spe- defined as a separate field. This was Agent-target interaction cific abnormalities at the molecular probably instigated by the completion Three maj
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