Association of dual-energy CT-derived quantitative parameters with hydroxyproline levels and pulmonary function in nonspecific interstitial pneumonia

Background This study evaluated the feasibility of dual-energy CT (DECT) for assessing the correlation between hydroxyproline (HYP) levels in lung tissue of patients with nonspecific interstitial pneumonia (NSIP) and lung volume and pulmonary function. Methods We retrospectively analyzed 99 NSIP patients (51 cellular, 48 fibrotic) and 40 controls. All underwent DECT imaging. Lung HYP‑equivalent density (HYP‑ED) and volume were quantified using spectral post-processing. Pulmonary function parameters, including FVC% Pred and DLCO% Pred, were collected. Intergroup differences, correlations, and diagnostic performance were assessed. Results Lung volume was higher in controls (3797.40 ± 1155.68 cc) than in cellular (2796.88 ± 334.03 cc) and fibrotic NSIP (2156.76 ± 423.40 cc; P < 0.001). HYP‑ED was lower in controls (206.29 ± 22.40 mg/cm 3 ) than in cellular (264.31 ± 24.99 mg/cm 3 ) and fibrotic NSIP (327.12 ± 36.26 mg/cm 3 ; P < 0.001), and lower in cellular than fibrotic NSIP ( P < 0.001). FVC% Pred and DLCO% Pred were higher in cellular NSIP (75.98 ± 4.07% and 69.96 ± 4.41%) than in fibrotic NSIP (71.44 ± 5.49% and 64.58 ± 3.38%; P < 0.05). HYP‑ED content showed significant negative correlations with lung volume and pulmonary function (all P < 0.01). HYP‑ED demonstrated excellent diagnostic performance for distinguishing NSIP subtypes (AUC 0.977), with 91.8% sensitivity and 92.9% specificity. Conclusions DECT enables noninvasive quantification of lung HYP-ED in NSIP. HYP‑ED correlates with disease severity and may serve as a promising imaging biomarker for fibrosis assessment and monitoring.