The Impact of CT Attenuation on Subsolid Pulmonary Nodule Detection With the Zero Echo Time MRI Technique

To investigate the association between CT attenuation and zero echo time (ZTE) MRI detectability of subsolid pulmonary nodules (SSNs), and to identify a potential attenuation threshold to inform radiation-free follow-up approaches.

Patients with SSNs ≤ 2 cm scheduled for surgical resection were prospectively enrolled between July 2022 and June 2023. Two radiologists reviewed nodule type (part-solid nodule [PSN] and ground-glass nodule [GGN]), size, location, and attenuation on preoperative CT, and evaluated detectability on ZTE-MRI. Associations between CT features, pathology, and ZTE-MRI detectability were analyzed using univariable and multivariable methods, and predictive performance was assessed with ROC curve analysis.

Thirty-nine patients with 64 SSNs (median diameter, 6.6 mm) participated in the study. Of these, 43 (67.2%) SSNs were identified on ZTE-MRI, including 11 PSNs (100%) and 32 GGNs (60.4%). CT attenuation was the most significant predictor for ZTE-MRI detectability (AUC, 0.993; P < .001), with an optimal threshold of -637.6 HU (sensitivity, 95.2%; specificity, 100.0%). Interreader agreement for ZTE-MRI measurements was high (intraclass correlation coefficient [ICC], 0.986). The size measurements between CT and ZTE-MRI demonstrated minimal bias, up to 0.3 mm. Surgical resection and pathological confirmation were performed for 47 SSNs. Detectable nodules were more frequently invasive adenocarcinomas (IACs) than undetectable nodules (94.1%, 32/34 vs. 30.8%, 4/13; P < .001).

ZTE-MRI detectability of SSNs was significantly associated with CT attenuation, with a potential threshold of -637.6 HU, and correlated with pathological invasiveness. These results may contribute to individualized follow-up protocols for SSNs initially identified by CT imaging.