Quantification of pulmonary inflammation by positron emission tomography in chronic obstructive pulmonary disease: a new horizon in the era of biomarkers?

Analysis of research trends and hot spots on COPD biomarkers from the perspective of bibliometrics

BACKGROUND

Chronic obstructive pulmonary disease (COPD), a chronic respiratory condition with airflow limitation, is the fourth leading global cause of death. Biomarkers are key for classifying COPD, detecting exacerbations, guiding treatment, and prognosis. This article uses bibliometrics and visualization to analyze COPD biomarker research trends, providing insights for future studies.

METHODS

This study adopts a range of literature analysis tools, including HistCite, VOSviewer, and CiteSpace, to systematically analyze literature on COPD biomarkers within the Web of Science Core Collection database from 2005 to 2024.

RESULTS

A total of 1835 papers or reviews related to COPD biomarkers are included in this study. Since 2003, the number of publications in this field has been on an upward trajectory. The United States being most influential in this field (n = 415, TLCS = 2319). Prominent institutions such as the University of British Columbia consistently deliver high-quality research results. Tal-Singer R, Sin DD, and Vestbo J have made significant contributions to COPD biomarker research. The journal American Journal of Respiratory and Critical Care Medicine is the most authoritative choice for researchers in the field.This research has long focused on biomarkers associated with the inflammatory response (C-reactive protein, eosinophils, etc.), pulmonary function, induced sputum, and computed tomography. Looking ahead, biomarkers such as microRNA, exosomes, DNA methylation, and microbiomics are likely to become popular topics, particularly regarding their roles in the prognosis and mechanisms of COPD.

CONCLUSION

Bibliometric analysis suggests that future research on COPD biomarkers will focus on advanced fields, such as microRNA, exosomes, DNA methylation, and microbiomics.

Imaging in alpha-1 antitrypsin deficiency: a window into the disease

Imaging modalities such as plain chest radiograph and computed tomography (CT) are important tools in the assessment of patients with chronic obstructive pulmonary disease (COPD) of any etiology. These methods facilitate differential diagnoses and the assessment of individual lung pathologies, such as the presence of emphysema, bullae, or fibrosis. However, as emphysema is the core pathological consequence in the lungs of patients with alpha-1 antitrypsin deficiency (AATD), and because AATD is associated with the development of other lung pathologies such as bronchiectasis, there is a greater need for patients with AATD than those with non-AATD-related COPD to undergo more detailed assessment using CT. In the field of AATD, CT provides essential information regarding the presence, distribution, and morphology of emphysema. In addition, it offers the option to quantify the extent of emphysema. These data have implications for treatment decisions such as initiation of alpha-1 antitrypsin (AAT) therapy, or suitability for surgical or endoscopic interventions for reducing lung volume. Furthermore, CT has provided vital insight regarding the natural history of emphysema progression in AATD, and CT densitometry has underpinned research into the efficacy of AAT therapy. Moving forward, hyperpolarized xenon gas (129Xe) lung magnetic resonance imaging (MRI) is emerging as a promising complement to CT by adding comprehensive measures of regional lung function. It also avoids the main disadvantage of CT: the associated radiation. This chapter provides an overview of technological aspects of imaging in AATD, as well as its role in the management of patients and clinical research. In addition, perspectives on the future potential role of lung MRI in AATD are outlined.

Quantitative analysis of dynamic 18F-FDG PET/CT for measurement of lung inflammation

Background

An inflammatory reaction in the airways and lung parenchyma, comprised mainly of neutrophils and alveolar macrophages, is present in some patients with chronic obstructive pulmonary disease (COPD). Thoracic fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) has been proposed as a promising imaging biomarker to assess this inflammation. We sought to introduce a fully quantitative analysis method and compare this with previously published studies based on the Patlak approach using a dataset comprising ¹⁸F-FDG PET scans from COPD subjects with elevated circulating inflammatory markers (fibrinogen) and matched healthy volunteers (HV). Dynamic ¹⁸F-FDG PET scans were obtained for high-fibrinogen (>2.8 g/l) COPD subjects (N = 10) and never smoking HV (N = 10). Lungs were segmented using co-registered computed tomography images and subregions (upper, middle and lower) were semi-automatically defined. A quantitative analysis approach was developed, which corrects for the presence of air and blood in the lung (qABL method), enabling direct estimation of the metabolic rate of FDG in lung tissue. A normalised Patlak analysis approach was also performed to enable comparison with previously published results. Effect sizes (Hedge’s g) were used to compare HV and COPD groups.

Results

The qABL method detected no difference (Hedge’s g = 0.15 [−0.76 1.04]) in the tissue metabolic rate of FDG in the whole lung between HV (μ = 6.0 ± 1.9 × 10⁻³ ml cm⁻³ min⁻¹) and COPD (μ = 5.7 ± 1.7 × 10⁻³ ml cm⁻³ min⁻¹). However, analysis with the normalised Patlak approach detected a significant difference (Hedge’s g = −1.59 [−2.57 −0.48]) in whole lung between HV (μ = 2.9 ± 0.5 × 10⁻³ ml cm⁻³ min⁻¹) and COPD (μ = 3.9 ± 0.7 × 10⁻³ ml cm⁻³ min⁻¹). The normalised Patlak endpoint was shown to be a composite measure influenced by air volume, blood volume and actual uptake of ¹⁸F-FDG in lung tissue.

Conclusions

We have introduced a quantitative analysis method that provides a direct estimate of the metabolic rate of FDG in lung tissue. This work provides further understanding of the underlying origin of the ¹⁸F-FDG signal in the lung in disease groups and helps interpreting changes following standard or novel therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0291-2) contains supplementary material, which is available to authorized users.

Advanced imaging in COPD: insights into pulmonary pathophysiology

Chronic obstructive pulmonary disease (COPD) involves a complex interaction of structural and functional abnormalities. The two have long been studied in isolation. However, advanced imaging techniques allow us to simultaneously assess pathological processes and their physiological consequences. This review gives a comprehensive account of the various advanced imaging modalities used to study COPD, including computed tomography (CT), magnetic resonance imaging (MRI), and the nuclear medicine techniques positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Some more recent developments in imaging technology, including micro-CT, synchrotron imaging, optical coherence tomography (OCT) and electrical impedance tomography (EIT), are also described. The authors identify the pathophysiological insights gained from these techniques, and speculate on the future role of advanced imaging in both clinical and research settings.