Application of low-dose FDG-PET/MRI for quantification of lung changes in pediatric patients with cystic fibrosis: a new inflammatory index.

Background: Clinical severity and progression of lung disease in cystic fibrosis (CF) are significantly influenced by the degree of lung inflammation. Non-invasive quantitative diagnostic tools are desirable to differentiate structural and inflammatory lung changes in order to help prevent chronic airway disease. This might also be helpful for the evaluation of longitudinal effects of novel therapeutics. Therefore, the present study assesses the quantification of inflammatory lung changes using positron emission tomography/magnetic resonance imaging (PET/MRI) of the lung in children and adolescents with CF and evaluates the possible impact of PET/MRI on individualized therapy management.

Methods: This monocentric, retrospective cohort study included 19 PET/MRI of the lung performed between 2014 and 2021 in 11 patients (16±4.5 years, 8-22 years; 7 females). PET acquisition was performed at least 20 minutes after i.v. application of a weight-adjusted dose of fluor-18-fluorodeoxyglucose (¹⁸F-FDG) of 1 MBq/kgBW (mean effective dose, 1.3±0.4 mSv). Lesions of increased uptake were quantified based on standardized uptake values (SUV) and compared to background activity, liver and blood pool. Pulmonary changes were assessed using the established magnetic resonance imaging-CF (MR-CF) score and correlated to inflammatory lesions. Results were correlated to changes in therapy (initiation, modification or discontinuation of therapy after baseline-PET/MRI) based on the electronic medical records.

Results: Uptake was highly increased in 5 cases, moderate in 4 cases, low in 7 cases, no uptake in 3 cases. Most MR-CF score points were assigned to peribronchitis (23%) and air trapping (23%). Metabolically increased lesions were mainly interpreted as consolidations (59%; P<0.001) and mucus plugging (19%, P=0.024). There was a decrease in mean number and volumes of inflammatory lesions (P=0.016 each) and MR-CF score (P=0.047) between baseline and follow-up. After PET/MRI, therapy changed in 18 cases (95%; new medication: 58%, n=11; termination of therapy: 16%, n=3; modification of therapy: 21%, n=4).

Conclusions: In selected cases, pulmonary FDG-PET/MRI can help guide therapeutic decision-making and provide complementary information on CF-related lung changes to conventional MRI at a low radiation exposure.