We wanted to evaluate the usefulness of dynamic magnetic resonance (MR) imaging for differentiating between benign and malignant solitary pulmonary nodules (SPNs).

Sixteen patients who had an undetermined SPN (<15 mm) upon chest computed tomography (8 males and 8 females; mean age: 55 years; age range: 40-76 years) underwent dynamic MR imaging. After the bolus injection of contrast material, the arterial (20-35 seconds), portal (45-60 seconds) and equilibrium (3-5 minutes) phase T1-weighted axial images were obtained with using a volumetric interpolated breath-hold examination. For discriminating the benign from malignant SPNs, the maximum relative enhancement ratio (MER) and the slope of the enhancement (SLE) were calculated and then they were statistically compared. With varying the threshold of the two indexes, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated.

The mean MER of the malignant SPN group was significantly higher than that of the benign SPN group (malignant; 0.56±0.17, benign; 0.43±0.17). With 0.33 as the threshold of MER for distinguishing the malignant SPN group from the benign SPN group, the sensitivity, specificity, positive predictive value and negative predictive value were 100%, 70%, 50%, and 100%, respectively. The mean SLE for the benign SPN group was higher than that for the malignant SPN group (malignant; m= 0.008±0.006/sec, benign; m=0.013±0.008/sec). With 0.025 as the threshold of the SLE, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 100%, 60%, 62.5%, 100% and 69.2%, respectively.

Dynamic MRI was useful for differentiating between benign and malignant SPNs. Moreover, MER and SLE might be good indexes for distinguishing benign SPNs from malignant SPNs.