Radiolabeled compounds in diagnosis of infectious and inflammatory disease

Nuclear medicine offers powerful noninvasive techniques for visualization of infectious and inflammatory disorders using whole body imaging enabling the determination of both localization and number of inflammatory foci. A wide variety of approaches depicting the different stages of the inflammatory response have been developed. Non-specific radiolabeled compounds, such as Ga-67-citrate and radiolabeled polyclonal human immunoglobulin accumulate in inflammatory foci due to enhanced vascular permeability. Specific accumulation of radiolabeled compounds in inflammatory lesions results from binding to activated endothelium (e.g. radiolabeled anti-E-selectin), the enhanced influx of leukocytes (e.g. radiolabeled autologous leukocytes, anti-granulocyte antibodies or cytokines), the enhanced glucose-uptake by activated leukocytes (F-18-fluorodeoxyglucose) or direct binding to micro-organisms (e.g. radiolabeled ciprofloxacin or antimicrobial peptides). Scintigraphy using autologous leukocytes, labeled with In-111 or Tc-99m, is still considered the "gold standard" nuclear medicine technique for the imaging of infection and inflammation, but the range of radiolabeled compounds available for this indication is still expanding. Recently, positron emission tomography with F-18-fluorodeoxyglucose has been shown to delineate various infectious and inflammatory disorders with high sensitivity. New developments in peptide chemistry and in radiochemistry will result in specific agents with high specific activity. A gradual shift from non-specific, cumbersome or even hazardous approaches to more sophisticated, specific approaches is ongoing. In this review, the different approaches to scintigraphic imaging of infection and inflammation, already in use or under investigation, are discussed.