Radionuclide Imaging of Inflammation and Infection in the Acute Care Setting

Although infection may be suggested by signs and symptoms such as fever, pain, general malaise, and abnormal laboratory results, imaging tests often are used to confirm its presence. Morphologic imaging tests identify structural alterations of tissues or organs that result from a combination of microbial invasion and the inflammatory response of the host. Functional imaging studies use minute quantities of radioactive material, which are taken up directly by cells, tissues, and organs, or are attached to substances that subsequently migrate to the region of interest. Bone scintigraphy is extremely sensitive and can be positive within 2 days after the onset of symptoms. With an accuracy of more than 90%, 3-phase bone scintigraphy is the radionuclide procedure of choice for diagnosing osteomyelitis in unviolated bone. In patients with acute renal failure, gallium imaging facilitates the differentiation of acute interstitial nephritis from acute tubular necrosis. Gallium imaging also is useful in the evaluation of pulmonary infections and inflammation. Many opportunistic infections affect the lungs, and a normal gallium scan of the chest excludes infection with a high degree of certainty, especially when the chest x-ray is negative. In the human immunodeficiency virus positive patient, lymph node uptake usually is associated with mycobacterial disease or lymphoma. Focal pulmonary parenchymal uptake suggests bacterial pneumonia. Diffuse pulmonary uptake suggests an opportunistic pneumonia. Gallium imaging provides useful information about other acute respiratory conditions, including radiation pneumonitis and hypersensitivity pneumonitis. In vitro labeled leukocyte imaging with indium-111 and technetium-99m labeled leukocytes is useful in various acute care situations. The test facilitates the differentiation of normal postoperative changes from infection and is useful for diagnosing prosthetic vascular graft infection. In inflammatory bowel disease, labeled leukocyte imaging is useful for initial screening, monitoring treatment response, detecting recurrent disease, and evaluating patients with discordant physical presentation and laboratory test results. Labeled leukocyte imaging, combined with bone marrow scintigraphy accurately diagnoses complicating osteomyelitis. Fluorine-18-fluorodeoxyglucose, imaging is rapidly completed and provides high-resolution images. This test is especially valuable in patients with fever of unknown origin, patients in septic shock, and mechanically ventilated patients suspected of harboring infection. Fluorine-18-fluorodeoxyglucose imaging also shows promise in inflammatory bowel disease.