Dynamic contrast-enhanced MR imaging for differentiation of rounded atelectasis from neoplasm

To characterize rounded atelectasis (RA) with dynamic contrast-enhanced MRI in the differential diagnosis of solitary peripheral pulmonary neoplasm.

Twenty-four patients with diagnostically equivocal peripheral pulmonary nodules were examined with dynamic contrast-enhanced MRI. 13 patients had a total of 16 rounded atelectases and 11 had a neoplasm. The final diagnosis was made either by histology (n = 14) or follow-up examinations of at least 24 months (n = 10). The peripheral nodules were evaluated concerning their morphology and contrast-enhancement dynamics. Curves for signal intensity (SI) versus time were produced and the relative increase in SI, slope of SI during wash-in, and slope of SI during wash-out calculated. Additionally, SI time curves were evaluated using a two compartment model where the ratio for the SI of the fast and the slow component were calculated. Mean values from different tissues of interest were compared by an unpaired two-sided t-test.

Analysis of the SI-time curves of the RAs revealed a curve shape similar to the pulmonary artery, but a magnitude in SI between artery and normal lung tissue. Linear curve fit showed a significantly steeper slope during wash-in and wash-out, and higher relative signal increase in atelectases as compared to neoplasms. Results from the two compartment model showed increased flow and a high ratio of the slow to the fast components with a long mean transit time in neoplasms.

Three parameters, slope of SI during wash-in and wash-out, and the slow/fast ratio can be used as diagnostic tools for discrimination of RA and neoplasm.