Radionuclide imaging in the evaluation of infections and inflammatory disease

111In leukocyte scintigraphy has high sensitivity and specificity for detecting abdominal and pelvic infections. For abdominal imaging, 111In leukocyte imaging is preferred to 67Ga citrate imaging. If localizing signs are present, CT is the preferred imaging technique. In the lungs, gallium imaging is preferred to leukocyte imaging for identifying active inflammatory processes. Gallium imaging provides quantitative information about inflammatory activity that is not apparent from chest CT scans. Although both gallium and leukocyte imaging have a role in patients with fever of unknown origin, gallium imaging may be preferred because it can be used to detect occult tumor as well as more chronic infectious foci. In patients who have AIDS, gallium imaging is particularly reliable in detecting and monitoring response to therapy of PCP. In febrile AIDS patients without localizing signs, 111In leukocyte scintigraphy is indicated to detect infection, except if PCP is suspected. In patients who have known tumor and fever, 111In leukocyte imaging may be preferred to gallium imaging to identify a source of infection. Most fevers in these patients appear to be due to tumor and chemotherapy, which would not manifest as an area of abnormality on an 111In leukocyte scan. If localizing symptoms are present, CT may be the preferred technique. The major concerns about 111In leukocytes are the hazards associated with withdrawal of blood, handling of blood, and reinjecting labeled cells and the requirement to delay imaging for 18 to 24 hours, thus precluding a rapid result. Potential replacement agents for 111In leukocytes include labeled immunoglobulins and labeled antigranulocyte antibody agents. The three- or four-phase bone scan is the first line diagnostic imaging technique after a plain radiograph in the evaluation of suspected osteomyelitis. If the bone scan is inconclusive, 111In leukocytes are the second line diagnostic imaging technique, particularly in adults with other bony abnormalities such as degenerative bone changes or trauma. Gallium imaging also may be used, preferably if other bony abnormalities are absent. In children, gallium imaging is the second line diagnostic imaging technique. Once the diagnosis has been made, gallium may be the preferred technique for following response to therapy.