Radionuclide imaging of infection

Although our understanding of microorganisms has advanced significantly and antimicrobial therapy has become increasingly available, infection remains a major cause of patient morbidity and mortality. The role of radionuclide imaging in the evaluation of the patient suspected of harboring an infection varies with the situation. For example, in the postoperative patient, radionuclide imaging is complementary to CT and is used to help differentiate postoperative changes from infection. In the case of the painful joint replacement, in contrast, radionuclide studies are the primary diagnostic imaging modality for differentiating infection from other causes of prosthetic failure. Several tracers are available for imaging infection: (99m)Tc-diphosphonates, (67)Ga-citrate, and (111)In- and (99m)Tc-labeled leukocytes. At the moment, in immunocompetent patients, labeled leukocyte imaging is the radionuclide procedure of choice for detecting most infections. There are, unfortunately, significant limitations to the use of labeled leukocytes. The in vitro labeling process is labor intensive, is not always available, and involves direct handling of blood products. For musculoskeletal infection, the need to frequently perform complementary marrow or bone imaging adds complexity and expense to the procedure and is an inconvenience to patients. Considerable effort has therefore been devoted to the search for alternatives to this procedure, including in vivo methods of labeling leukocytes, (18)F-FDG PET, and radiolabeled antibiotics. This article reviews the current status of nuclear medicine infection imaging and the potential of a murine monoclonal antigranulocyte antibody, fanolesomab, that is currently under investigation. Upon completion of this article, the reader will be familiar with the physical characteristics and uptake mechanisms of tracers currently approved for infection imaging, the indications for the uses of these tracers, and the characteristics and potential indications for a murine monoclonal antigranulocyte antibody under investigation.