Efficacy of zero echo time pulmonary MRI for RECIST 1.1 response classification in lung cancer: a prospective study

Accurately assessing treatment response in stage III/IV lung cancer is critical for guiding treatment decisions and evaluating patient prognosis. Thin-slice computed tomography (CT) is a commonly used imaging method for this assessment. However, repeated or long-term CT follow-up carries the risk of cumulative ionizing radiation exposure. As an emerging radiation-free technology, zero echo time (ZTE) magnetic resonance imaging (MRI) has demonstrated potential for visualizing pulmonary structures. Therefore, this study aims to evaluate the efficacy of ZTE for response classification in stage III/IV lung cancer by comparing it with thin-slice CT.

A prospective study was conducted in 47 patients with stage III/IV lung cancer. During the follow-up period, all patients underwent free-breathing ZTE, breath-hold ZTE, and CT scans. The maximum diameter of target lesions, the sum of maximum diameters, the occurrence of new pulmonary lesions, and the efficacy classification were compared among free-breathing ZTE, breath-hold ZTE, and CT images. The weighted kappa coefficient was applied to assess the pairwise intermodality agreement in response classification. Intermodality and interobserver agreements for the maximum diameters of target lesions were evaluated using intraclass correlation coefficients (ICC). The Friedman test, Spearman's correlation, median absolute deviation (MAD), median percentage error (MPE), and Bland-Altman analysis were used to evaluate the agreement between modalities.

The maximum diameter and sum of maximum diameters of target lesions among free-breathing ZTE, breath-hold ZTE, and CT showed no significant difference (Chi-squared =0.081, P=0.960; Chi-squared =0.096, P=0.953), and both ZTE modalities exhibited extremely high intermodality consistency with CT (ICC =0.995 and 0.993, respectively). New lesion detection showed a 100% detection rate for both free-breathing and breath-hold ZTE compared with CT. For Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 classification, free-breathing ZTE and breath-hold ZTE demonstrated excellent intermodality agreement with CT (kappa =0.959 and 0.832, respectively), and excellent agreement between ZTE modalities was also observed (kappa =0.877).

Free-breathing ZTE, breath-hold ZTE, and CT demonstrated similar performance during lung cancer follow-up. However, further validation through large-sample, multi-center prospective studies is still required.