Parameter response mapping does not enhance the correlations of conventional CT quantitative metrics with lung...

Parameter response mapping (PRM) has been employed in chronic obstructive pulmonary disease (COPD) assessments, providing a more accurate characterization of emphysema and air trapping. This study aimed to evaluate and compare the correlations of PRM and conventional computed tomography (CT) quantitative metrics with lung function and subjective symptoms in COPD patients.

A total of 94 COPD patients were prospectively enrolled who underwent inspiratory and expiratory dual-phase CT scans and pulmonary function tests (PFTs) at The Second People's Hospital of Quzhou from January 2023 to June 2024. PRM parameters (emphysema area, PRM^EMPH; functional small airway disease area, PRM^fSAD; normal lung parenchyma area, PRM^NORM), conventional CT quantitative parameters on inspiratory CT [mean lung density on inspiratory CT, MLD_IN; 15th percentile of lung attenuation value on inspiratory CT, P_15IN; percentage of low attenuation area ≤-950 Hounsfield units (HU) on inspiratory CT, LAA%_-950IN] and on expiratory CT (mean lung density on expiratory CT, MLD_EX; 15th percentile of lung attenuation value on expiratory CT, P_15EX; percentage of low attenuation area ≤-856 HU on expiratory CT, LAA%_-856EX), PFT parameters [forced expiratory volume in 1 second (FEV₁); forced vital capacity (FVC); FEV₁/FVC; FEV₁ percent of the predicted value (FEV₁%Pred)], and subjective symptom scores [modified Medical Research Council dyspnea scale (mMRC); COPD Assessment Test (CAT)] were obtained. Correlations between PRM parameters and both PFT outcomes and subjective symptom scores were compared to those between conventional CT quantitative parameters and both PFT outcomes and subjective symptom scores.

Both PRM and conventional CT quantitative parameters correlated with PFT outcomes. Notably, strong correlations were observed for both FEV₁ vs. PRM^NORM (r=0.839) and FEV₁ vs. LAA%_-856EX (r=-0.840). However, no significant difference was found between these two correlation coefficients (z=-0.023, P=0.982). Similarly, correlations for both FEV₁%Pred versus PRM^NORM (r=0.885) and FEV₁%Pred versus LAA%_-856EX (r=-0.887), and no significant difference between them (z=-0.063, P=0.950). mMRC and CAT scores correlated well with PRM and conventional CT quantitative parameters, particularly with PRM^NORM and LAA%_-856EX (r=-0.790, 0.784 for mMRC and r=-0.814 and 0.812 for CAT, respectively), and no significant difference between these two sets of r values (z=0.106, P=0.915 for mMRC and z=0.040, P=0.968 for CAT, respectively).

PRM metrics demonstrated strong correlations with pulmonary function and patients' subjective symptom scores, particularly PRM^NORM, which reflects lung function and patients' subjective symptoms effectively. However, in this cross-sectional cohort, PRM^NORM did not demonstrate stronger whole-lung associations with lung function or symptom burden compared to the conventional dual-phase CT parameter LAA%_-856EX.