Molecular Imaging of Pulmonary Inflammation and Infection

Infectious and inflammatory pulmonary diseases are a leading cause of morbidity and mortality worldwide. Although infrequently used in this setting, molecular imaging may significantly contribute to their diagnosis using techniques like single photon emission tomography (SPET), positron emission tomography (PET) with computed tomography (CT) or magnetic resonance imaging (MRI) with the support of specific or unspecific radiopharmaceutical agents. ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG), mostly applied in oncological imaging, can also detect cells actively involved in infectious and inflammatory conditions, even if with a low specificity. SPET with nonspecific (e.g., ⁶⁷Gallium-citrate (⁶⁷Ga citrate)) and specific tracers (e.g., white blood cells radiolabeled with ¹¹¹Indium-oxine (¹¹¹In) or ^99mTechnetium (^99mTc)) showed interesting results for many inflammatory lung diseases. However, ⁶⁷Ga citrate is unfavorable by a radioprotection point of view while radiolabeled white blood cells scan implies complex laboratory settings and labeling procedures. Radiolabeled antibiotics (e.g., ciprofloxacin) have been recently tested, although they seem to be quite unspecific and cause antibiotic resistance. New radiolabeled agents like antimicrobic peptides, binding to bacterial cell membranes, seem very promising. Thus, the aim of this narrative review is to provide a comprehensive overview about techniques, including PET/MRI, and tracers that can guide the clinicians in the appropriate diagnostic pathway of infectious and inflammatory pulmonary diseases.