MR imaging in peripheral lung lesions

Recently, chest computed tomography (CT) has become the most widely available modality for evaluation of peripheral lung lesions. However the diagnostic accuracy of CT is low; CT alone is not sufficient for deciding on a treatment plan. We use magnetic resonance imaging (MRI) to enhance imaging diagnosis. From April 2005 to December 2005, 75 patients underwent surgical operation in our division. Forty-three patients, each with a preoperatively recognized peripheral lung lesion underwent MRI study. The 43 patients were classified into two groups by pathological examination: malignant lesions (n=37, including 30 patients with primary cancer and 7 patients with metastatic cancer), and non-malignant lesions (n=6). Short TI inversion recovery (STIR), high b-value diffusion weighted imaging (DWI) with free breathing scanning and dynamic MRI study were performed, and the two groups were statistically compared. STIR and DW imaging were visually classified on a scale of 1-4 by signal intensity. Moderate (score 3) and strong signal (score 4) intensity on DWI was significantly greater in malignant lesions (30 of 37; 81.1%) than in non-malignant lesions (2 of 6; 33.3%). When the lesions demonstrated a strong enhancement (steep type) in dynamic study or moderate and strong signal intensity on DWI, we judged them as positive. Sensitivity, specificity and accuracy were 86.5%, 66.7%, and 83.7%, respectively. All of the false negative cases (n=5) were pathologically non-invasive cancer with stage IA and small-sized adenocarcinoma. In the diagnosis of peripheral lung lesions, high b-value DWI could be valuable as a supporting tool in differentiating non-invasive cancer (Type A or B on Noguchi's classification etc.). (author)