Oxygen-Enhanced ZTE-MRI for Pulmonary Nodule Assessment: A Comparative Study with CT

Abstract

Background: Frequent computed tomography (CT) scans for pulmonary nodule monitoring (every 3, 6, and 12 months) lead to increased radiation exposure and a potential risk of malignancy. Although lung magnetic resonance imaging (MRI) is gradually approaching CT in terms of performance, the effectiveness of zero-echo-time (ZTE) sequences remains to be fully optimized, particularly in terms of diagnostic accuracy under the Lung-RADS.

Objective: This study aimed to evaluate the feasibility of oxygen-enhanced (OE) ZTE-MRI at varying oxygen concentrations (21% and 100%) for both the subjective and objective assessment of pulmonary nodules. It further explored the potential of OE-ZTE-MRI in detecting nodules, its diagnostic utility in Lung-RADS classification, and its role in evaluating malignant potential.

Methods: A total of 68 participants who underwent CT, ZTE-MRI, or OE-ZTE-MRI, were enrolled in this study. Quantitative MRI parameters (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) were used to evaluate image quality. Lung nodule detection and Lung-RADS classification were performed by two radiologists independently using observer-based scoring of structural features: nodule type (solid nodule [SN], part-solid nodule [PSN], and ground-glass nodule [GGN]), and nodule size (measured manually on CT, ZTE-MRI, and OE-ZTE-MRI). Statistical analyses included the Wilcoxon signed-rank test, percentage consistency, kappa values, intraclass correlation coefficient (ICC), Spearman`s correlation, and Bland-Altman analysis. Statistical significance was set at p < 0.05.

Results: Among the 68 patients (80 nodules; 57.2 ± 10.7 years; 27 males), OE-ZTE-MRI demonstrated a significantly higher SNR (p < 0.05) and superior qualitative scoring compared to ZTE-MRI. The nodule detection rate for OE-ZTE-MRI was 87.5%, with a diagnostic performance comparable to that of CT for assessing nodule diameter (ICC: 0.997; r = 0.994). OE-ZTE-MRI showed a high agreement with CT in nodule characterization (kappa = 0.789) and Lung-RADS (kappa = 0.756). Additionally, OE-ZTE-MRI exhibited strong inter-observer consistency in nodule size measurements.

Conclusion: OE-ZTE-MRI, which incorporates oxygen concentration adjustments, outperformed conventional ZTE-MRI in both subjective and objective evaluations. It achieves diagnostic performance comparable to that of CT in terms of nodule size. According to the Lung-RADS classification, OE-ZTE-MRI is gradually approaching the same diagnostic accuracy as CT.

Keywords: CT; Lung-RADS; Pulmonary nodules; ZTE.