Infection Inflammation and Musculoskeletal
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Radionuclide imaging of patients with infection/inflammation is based on different agents and procedures, with varying degrees of complexity. While relatively simple techniques (such as, e.g., three-phase bone scintigraphy in case of suspected osteomyelitis of the extremities) rely on indirect scintigraphic visualization of the pathophysiologic events associated with the process (such as local hyperperfusion, edema, osteoblastic reaction), other techniques employ radiopharmaceuticals that accumulate “specifically” at the site of infection. Perhaps the oldest tracer of this category is 67Ga-citrate, an agent that targets transferrin and lactoferrin receptors (that are abundantly expressed on the cell surface of granulocytes and of other inflammatory cells). The most accurate radionuclide infection-imaging are based on direct labelling of leukocytes (mostly granulocytes), which is achieved either by systemic administration of certain radiopharmaceuticals (such as, e.g., anti-granulocyte antibodies) or by isolation of autologous leukocytes from the patient’s own peripheral blood, their labelling through in-vitro incubation with adequate radiotracers (such as, e.g., 111In-oxine or 99mTc-HMPAO), followed then by their re-infusion into the patient. More recent developments rely on PET with [18F]FDG, based on increased (though nonspecific) accumulation of this agent at sites of abnormally enhanced metabolism (such as tumours or infection). Also in the case of infection imaging, the highest clinical benefit is achieved by relying on tomographic imaging (SPECT or PET), preferably with hybrid image fusion analysis (SPECT/CT or PET/CT).