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Can Malignant and Benign Pulmonary Nodules Be Differentiated with Diffusion-Weighted MRI?

¹ Department of Radiology, Ohme Municipal General Hospital, 4-16-5, Higashi-Ohme, Ohme City, Tokyo 198-0042, Japan.
² Department of Pulmonary Medicine, Ohme Municipal General Hospital, Ohme City, Tokyo, Japan.
³ Present address: Department of Pulmonary Medicine, National Printing Bureau Tokyo Hospital, Tokyo, Japan.
⁴ Department of Pathology, Ohme Municipal General Hospital, Ohme City, Tokyo, Japan.
⁵ Present address: Department of Pathology, Kurashiki Medical Center, Kurashiki, Japan.
⁶ Present address: Department of Pulmonary Medicine, Graduate School of Tokyo Medical and Dental University, Tokyo, Japan.

OBJECTIVE. The objective of our study was to evaluate whether diffusion-weighted imaging (DWI) with a high b factor can be used to differentiate malignancies from benign pulmonary nodules.

MATERIALS AND METHODS. This study included 54 pulmonary nodules ( 5 mm in diameter) in 51 consecutive patients (37 men, 14 women; mean age, 65.7 years; age range, 31–88 years). Thirty-six (67%) of the 54 pulmonary nodules were malignant, and 18 (33%) were benign. Two radiologists independently reviewed the signal intensity of the nodules on DWI with a b factor of 1,000 s/mm² using a 5-point rank scale without knowledge of clinical data. This scale was based on the following scores: 1, nearly no signal intensity; 2, signal intensity between 1 and 3; 3, signal intensity almost equal to that of the thoracic spinal cord; 4, higher signal intensity than that of the spinal cord; and 5, much higher signal intensity than that of the spinal cord. The Mann-Whitney U test and the receiver operating characteristic (ROC) curve were used to calculate the difference between the scores of malignant and benign nodules.

RESULTS. On DWI, the mean score of malignant pulmonary nodules (4.03 ± 1.16 [SD]) was significantly higher (p < 0.01) than that of benign nodules (2.50 ± 1.47), with an area under the ROC curve of 0.796 (95% CI, 0.665–0.927). When a score of 3 was considered as a threshold, the sensitivity, specificity, and accuracy were 88.9% (95% CI, 78.6–99.2%), 61.1% (38.6–83.6%), and 79.6% (68.9–90.3%), respectively. Three small metastatic nodules (13, 16, and 20 mm) and one bronchioloalveolar carcinoma scored 1 or 2 on the 5-point rank scale. Three granulomas, two active inflammatory lung nodules, and one fibrous nodule scored 4 or 5.

CONCLUSION. The signal intensity of pulmonary nodules may be useful for malignant and benign differentiation on DWI. However, the interpretation of small metastatic nodules, nonsolid adenocarcinoma, some granulomas, and active inflammatory nodules should be approached with caution.

Keywords: b factor • diffusion-weighted imaging • lung cancer • MRI • pulmonary nodules

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