Molecular Imaging of Pulmonary Inflammation and Infection

Abstract

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.

Coronavirus Disease 2019 (COVID-19) in Molecular Imaging: A Systematic Review of Incidental Detection of SARS-CoV-2 Pneumonia on PET Studies

“…Although 18 F-fluorodeoxyglucose ( 18 F-FDG) PET/CT is not usually applied in the diagnosis of acute pneumonia, its clinical value in the pulmonary inflammatory/infectious conditions has already been explored 10 . Besides, 18 F-FDG PET can assess the severity of disease, monitor disease progression, and evaluate the post-therapy response 11 . More importantly, the whole-body PET/CT imaging offers a unique chance to evaluate the possible extrapulmonary manifestations of COVID-19.…”

Current Applications for Nuclear Medicine Imaging in Pulmonary Disease

“…VQ SPECT can help to detect early COPD as the scintigraphic findings correlate with spirometric data and extent of emphysema [ 16 ]. Technegas ventilation scintigraphy also shows correlation with spirometry and appears promising in the diagnosis and grading of chronic obstructive pulmonary disease (COPD) [ 17 ] as well as monitoring treatment response in asthma [ 18 ].…”

“…Diffuse 67 Ga uptake in lungs is nonspecific, which can be seen in various infectious and inflammatory conditions. Due to long testing time, high frequency of false positive results, relatively high radiation dose, and availability of other modalities (PET/CT), the role of 67 Ga scintigraphy in clinical practice has been reduced [9,18].…”

“…Per European Association of Nuclear Medicine (EANM) guidelines [28], labeled WBC scintigraphy may be used to detect, localize, and determine the extent of the process in occult lung infection disorders, as well as fever of unknown origin (FUO), endocarditis, postoperative abscesses, infected central venous catheters, or other vascular devices. Disadvantages of scintigraphy with radiolabeled WBC are the requirement of blood handling for radiopharmaceutical preparation, the longer duration of the procedure compared with 18 F-2-deoxyglucose (FDG) PET/CT, and lower spatial resolution. Labeled leukocyte with SPECT/CT imaging is a sensitive test for detecting lung infection, it can be especially beneficial in immunocompromised patients, and a study by Love et al showed that absence of focal pulmonary activity had a 99% negative predictive value for excluding pulmonary infection [29].…”

“…99m Tc-ethambutol planar and SPECT/CT scintigraphy has been shown to be useful in tuberculosis with high sensitivity and specificity for detection of pulmonary and extrapulmonary disease [60]. Viral infections could be potentially detected with the help of an emerging radiopharmaceutical for PET/CT studies; for example, 18 F-fluoro-5-ethyl-1beta-D-arabinofuranosyluracil ( 18 F-FEAU) recognizes an enzyme produced by herpes simplex virus [61]. Many new PET radiopharmaceuticals for infection imaging have been tested in preclinical trials with potential to be translated to humans [62].…”