Molecular Imaging of Inflammation and Infection

In spite of advances in its prevention and treatment, infection remains a major cause of morbidity and mortality throughout the world. While symptoms, signs, and abnormal laboratory tests may suggest infection, the diagnosis is not always obvious, and imaging tests often are used for confirmation and localization. Radiologic imaging such as X-rays, computed tomography, magnetic resonance imaging, and ultrasonography depicts structural alterations in tissues and organs that are caused by a combination of the infection itself and the host’s response to the infection. Molecular imaging procedures utilizing radiopharmaceuticals, such as labeled leukocytes, gallium, and fluorodeoxyglucose, reflect the physiological changes that are part of the inflammatory process. Currently, gallium-67 citrate imaging is used for differentiating interstitial nephritis from acute tubular necrosis and as a substitute for ¹⁸F-FDG for indications such as sarcoid, spondylodiscitis, and fever of unknown origin, when the latter is not available. In vitro labeled leukocyte imaging is the imaging test of choice for most infections in the immunocompetent population. Over the past two decades, ¹⁸F-FDG has established itself as the molecular imaging agent of choice for fever of unknown origin, vasculitis, sarcoid, and spondylodiscitis. This chapter reviews the role of these agents in the detection and localization of inflammation and infection.