Abstract: Objective  To explore the value of MRI，especially contrast-enhanced MRI and diffusion weighted imaging (DWI) in differentiating parenchymal tuberculosis from brain metastases of lung cancer.  Methods  The conventional MRI and DWI were performed in 82 cases (42 cases with parenchymal tuberculosis, and 40 cases with brain metastases from lung cancer). The mean apparent diffusion coefficient (ADC) values and relative apparent diffusion coefficient (rADC) values were calculated from the lesions. Datas are analyzed by SPSS 13.0 software packet, and using t test.  Results  Forty-two cases of parenchymal tuberculosis all showed multi-focus, 82.56% (374/453) of lesions were smaller than 1.0 cm,33.77% (153/453) of lesions were evenly enhanced with nodosity, the others showed ring-like contrast enhancement on Gd-DTPA enhanced T₁WI,and the rim had uniform thickness, the inner and outer walls were smooth. About 36.42% (165/453) of lesions had mild or moderate edema. 32.50% (13/40) of brain metastases from lung cancer showed solitary, 41.01% (57/139) of lesions were smaller than 1.0 cm, 4.32% (6/139) of lesions were evenly enhanced with nodosity, the others showed ring-like or patchy contrast enhancement on Gd-DTPA enhanced T₁WI, About 19.17% (23/120) of the rims showed uniform thickness, the others were coarse or accompanied by a nodule. About 75.54% (105/139) of lesions had moderate or severe edema.The ADC values of the solid center and the rim of parenchymal tuberculosis were (0.97±0.15）×10^-3 mm²/s,（1.07±0.20）×10^-3mm²/s, they were lower than the ADC values from the solid and cystic lesions of brain meta-stases from lung cancer which were（1.10±0.25）×10-³mm²/s and（1.28±0.32）×10^-3mm²/s respectively, there was statistical significance.  Conclusion  Contrast-enhanced MRI could clearly display the morphological features, size and adjacent relationships of parenchymal tuberculosis and brain metastases from lung cancer, DWI and the ADC values could display the alterations of the microscopic structure of the tissue. Combination of contrast-enhanced MRI and DWI are helpful in diagnosis and differential diagnosis of these two diseases.

Key words: Tuberculosis,meningeal/diagnosis, Lung neoplasms, Brain neoplasms, Magnetic resonance imaging