Comparison of Pulmonary Nodule Morphology on Pre-Contrast and Delayed Post-Contrast Stack-of-Spirals Ultrashort Echo Time MRI

Background: Stack-of-spirals ultrashort TE (spiral-UTE) MRI has shown promise for radiation-free pulmonary nodule detection, and previous studies have reported closely matched observed pulmonary nodule detection rates between contrast-enhanced (UTEe) and unenhanced (UTEu) acquisitions. However, whether this performance extends to detailed lesion-level morphological characterization and whether delayed post-contrast spiral-UTE provides additional morphological information compared with the pre-contrast acquisition under the clinical imaging protocol remain incompletely understood. Therefore, this study compared UTEu and UTEe for lesion-level morphological assessment using CT as the reference standard. Methods: A total of 61 patients with pulmonary nodules/masses (>5 mm) identified on chest CT were enrolled. Patients underwent spiral-UTE MRI on either a 1.5 T scanner (27 patients, 63 lesions) or a 3.0-T scanner (34 patients, 101 lesions). Two fixed consensus reader panels with different experience profiles evaluated lesion visualization and detailed morphological features separately on sequential pre-contrast UTEu and delayed post-contrast UTEe. Two complementary morphology analyses were performed. First, end-to-end successful characterization was assessed across all CT-detected eligible lesions; for each feature, successful characterization required both lesion visualization on the corresponding UTE acquisition and correct feature classification relative to CT. Nonvisualized lesions were designated not characterizable and therefore unsuccessful for this composite outcome. Second, conditional sensitivity, specificity, and accuracy were evaluated among lesions visualized on both UTEu and UTEe to compare morphology interpretation after successful lesion visualization. Lesion size agreement, contrast-to-noise ratio (CNR), and edge sharpness were also evaluated. Results: CT identified 164 lesions, of which the experienced consensus panel visualized 113/164 lesions (68.9%) on both UTEu and UTEe, three on UTEu only, three on UTEe only, and 45 on neither; the inexperienced panel visualized 93/164 lesions (56.7%) on UTEu and 91/164 (55.5%) on UTEe; 91 lesions were visible on both acquisitions, two on UTEu only, none on UTEe only, and 71 on neither. In field-strength-stratified end-to-end analyses, successful-characterization rates ranged from 55 to 71% for UTEe, and 51 to 71% for UTEu derived from experienced reader panel. Among common-visible lesions, no statistically detectable UTEu–UTEe differences were demonstrated for most evaluated morphological features. Conclusions: Across all CT-detected lesions, the ability of spiral-UTE to accurately characterize pulmonary nodule morphology was constrained by incomplete lesion visualization. Our analyses did not demonstrate a statistically detectable UTEu–UTEe difference for most evaluated morphological features. Among UTE-visible lesions, both acquisitions showed relatively high accuracy for several morphological features.