Topologic Parametric Response Mapping Identifies Tissue Subtypes Associated with Emphysema Progression.

Area of Science:

• Pulmonary Medicine
• Radiology
• Medical Imaging Analysis

Background:

• Small airways disease (SAD) and emphysema are key components of chronic obstructive pulmonary disease (COPD).
• Predicting COPD progression is challenging due to disease heterogeneity.
• SAD is a primary cause of airflow obstruction in mild COPD and a precursor to emphysema.

Purpose of the Study:

• To investigate if the distribution of CT-based Parametric Response Mapping (PRM) of functional SAD (fSAD) is associated with emphysema progression.
• To characterize COPD progression patterns using topological PRM analysis.
• To identify radiologic subtypes of COPD based on PRM classifications.

Main Methods:

• Analysis of paired inspiratory-expiratory chest CT scans from 1495 COPDGene subjects at baseline and 5-year follow-up.
• Topological analyses of PRM classifications with spatial alignment of temporal scans.
• K-means clustering for subject subtyping and assessment of PRM values, pulmonary function, and clinical measures.

Main Results:

• Three radiologic subtypes were identified: emphysema-dominant (ED), fSAD-dominant (FD), and fSAD-transition (FT).
• The FT subtype exhibited the most rapid local emphysema progression (-57.5% ± 1.1) compared to FD (-49.9% ± 0.5) and ED (-33.1% ± 0.4) at year five.
• Approximately 60% of FT subjects were classified as at-risk with normal spirometry.

Conclusions:

• The fSAD-transition (FT) subtype may enable earlier identification of individuals at risk for emphysema development.
• This subtype can be identified in individuals who do not yet meet spirometric criteria for COPD.
• CT-based PRM offers a method to characterize COPD progression and identify at-risk populations.