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Evaluation of Idiopathic Pulmonary Fibrosis by 18F-FDG PET-CT Scan: Importance of the Correction for the Density in the Interpretation of the Results
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A2337 - Evaluation of Idiopathic Pulmonary Fibrosis by 18F-FDG PET-CT Scan: Importance of the Correction for the Density in the Interpretation of the Results
Author Block: A. Castiaux, G. Van Simaeys, S. Goldman, B. Bondue; Hôpital Erasme, ULB, Brussels, Belgium.
Introduction
Idiopathic Pulmonary Fibrosis (IPF) is a progressive and irreversible disease leading to a terminal respiratory insufficiency. Its clinical course is unpredictable and biomarkers of its activity are actively searched. Among these, the role of fluorodeoxyglucose (18F-FDG) PET-CT imaging has been recently studied showing correlations between 18F-FDG lung uptake and severity of the disease. However, regional changes in lung density characterize IPF and affect the proportion of actual pulmonary tissue within any lung volume in which FDG uptake is calculated. Still, changes in lung density were generally not taken into account in previous 18F-FDG PET studies, leaving open the question of a relationship between the severity of the disease and metabolic activity of the pulmonary tissue itself, whatever its proportion in the lung volume — i.e. independently of disease-related changes in lung density. The aim of this study was therefore to correlate severity and evolution of IPF to lung uptake of 18F-FDG, evaluated by mean and maximum standardized uptake value (SUV), corrected (SUVmean-corr; SUVmax-corr) and uncorrected for lung density (SUVmean-uncorr; SUVmax-uncorr).
Methods
18F-FDG PET-CT was performed in 31 IPF patients between 2013 and 2017. Lung density was determined on CT and SUV values were correlated with lung function test, DLCO and 6-minute walking test (6MWT) at baseline and at one year.
Results
At baseline, SUVmean-uncorr was highly correlated with lung density and lung volume (VC, FVC, TLC), while SUVmean-corr was not. Lung density was furthermore highly correlated with lung volumes. Interestingly, SUVmean-corr was significantly higher in patients with a GAP score of 3, and negatively correlated with DLCO and desaturation during the 6MWT. Baseline SUVmean-corr was also correlated with increasing desaturation (>5%) during the 6MWT at one year whereas no correlation was found with changes in lung volume, walk distance and DLCO at one year.
Conclusion
18F-FDG uptake evaluated with no correction for lung density is tightly related to the severity of the disease; this relation is strongly influenced by the lung density since it disappears when the correction for lung density is applied. To evaluate the intrinsic activity of the disease with 18F-FDG at the pulmonary tissue level, this correction appears necessary. We found no correlation between corrected SUV and most indices of clinical evolution at one year, but this is possibly related to the small number of patients and the short-term evaluation. Further studies in larger populations and a longer follow-up are therefore warranted.
Author Block: A. Castiaux, G. Van Simaeys, S. Goldman, B. Bondue; Hôpital Erasme, ULB, Brussels, Belgium.
Introduction
Idiopathic Pulmonary Fibrosis (IPF) is a progressive and irreversible disease leading to a terminal respiratory insufficiency. Its clinical course is unpredictable and biomarkers of its activity are actively searched. Among these, the role of fluorodeoxyglucose (18F-FDG) PET-CT imaging has been recently studied showing correlations between 18F-FDG lung uptake and severity of the disease. However, regional changes in lung density characterize IPF and affect the proportion of actual pulmonary tissue within any lung volume in which FDG uptake is calculated. Still, changes in lung density were generally not taken into account in previous 18F-FDG PET studies, leaving open the question of a relationship between the severity of the disease and metabolic activity of the pulmonary tissue itself, whatever its proportion in the lung volume — i.e. independently of disease-related changes in lung density. The aim of this study was therefore to correlate severity and evolution of IPF to lung uptake of 18F-FDG, evaluated by mean and maximum standardized uptake value (SUV), corrected (SUVmean-corr; SUVmax-corr) and uncorrected for lung density (SUVmean-uncorr; SUVmax-uncorr).
Methods
18F-FDG PET-CT was performed in 31 IPF patients between 2013 and 2017. Lung density was determined on CT and SUV values were correlated with lung function test, DLCO and 6-minute walking test (6MWT) at baseline and at one year.
Results
At baseline, SUVmean-uncorr was highly correlated with lung density and lung volume (VC, FVC, TLC), while SUVmean-corr was not. Lung density was furthermore highly correlated with lung volumes. Interestingly, SUVmean-corr was significantly higher in patients with a GAP score of 3, and negatively correlated with DLCO and desaturation during the 6MWT. Baseline SUVmean-corr was also correlated with increasing desaturation (>5%) during the 6MWT at one year whereas no correlation was found with changes in lung volume, walk distance and DLCO at one year.
Conclusion
18F-FDG uptake evaluated with no correction for lung density is tightly related to the severity of the disease; this relation is strongly influenced by the lung density since it disappears when the correction for lung density is applied. To evaluate the intrinsic activity of the disease with 18F-FDG at the pulmonary tissue level, this correction appears necessary. We found no correlation between corrected SUV and most indices of clinical evolution at one year, but this is possibly related to the small number of patients and the short-term evaluation. Further studies in larger populations and a longer follow-up are therefore warranted.
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