| OBJECTIVE: (1) To evaluate the effect of intravenous Gd-DTPA on both ADC and FA values of DTI for brain tumors;(2) To explore the values of DTI in the differential diagnosis of low-grade cerebral gliomas , cerebral infarctions and viral encephalitis.METHODS: The conventional MR imaging and diffusion tensor imaging(DTI) were performed on 83 cases with brain tumors (including 22 cases with low-grade cerebral gliomas, 30 cases with high-grade cerebral gliomas, 28 cases with metastatic tumors and 3 cases with lymphomas ), 26 cases with acute or subacute cerebral infarctions and 18 cases with acute or subacute viral encephalitis before treatments or operations between October, 2009 and August, 2010. We also performed other twice DTI examinations after Gd-DTPA intravenous adminstration injection in 27 cases with brain tumors. The diagnoses were confirmed surgically and pathologically in cases with brain tumors except 19 cases with metastatic tumors which had primary tumor and typical MR imaging, and the diagnoses were made clinically in cases with cerebral infarctions or viral encephalitis. DTI were performed using single shot SE-EPI sequence with two different b values(0 s/mm2 and 1000 s/mm2). DTI were performed immediately before Gd-DTPA intravenous adminstration injection. The second and the third DTI scan in 27 cases with brain tumors were performed immediately after (0 min) and 7 min following the confirmed end of Gd-DTPA intravenous adminstration injection. The data measured from DTI were calculated and analyzed, and then statistical analyses were performed by using the software of SPSS 11.5.RESULTS: (1) Significant differences between pre-contrast and post-contrast were shown in both ADC and FA values of the enhanced regions of brain tumors (P<0.01), but there was no significant difference between post-contrast 0 min and 7 min (P>0.05). In the ADC and FA values of the edema, contralateral normal brain tissue and normal corpus callosum, there were no any significant differences among pre-contrast, post-contrast 0 min and 7 min (P>0.05). (2) The mean ADC values, rADC values, FA values and rFA values were(1.55±0.08)×10-3mm2/s, 1.68±0.25, 0.17±0.03 and 0.42±0.08 in cases with low-grad cerebral gliomas respectively; (0.54±0.12)×10-3mm2/s, 0.64±0.12, 0.14±0.03 and 0.30±0.05 in cases with cerebral infarctions respectively; (0.84±0.07)×10-3mm2/s, 1.07±0.05, 0.17±0.02 and 0.43±0.09 in cases with viral encephalitis. There were significant differences in the mean ADC values and rADC values (P < 0.01) among the three groups. The ADC values and rADC values of the low-grade cerebral gliomas were the highest one and those of the cerebral infarctions were the lowest one. There were significant differences in the mean FA values and rFA values (P <0.01) between low grade cerebral gliomas and cerebral infarctions , so were between viral encephalitis and cerebral infarctions. But there weren't any significant differences in the mean FA values and rFA values (P > 0.05) between low grade cerebral gliomas and viral encephalitis.CONCLUSION: (1) The ADC values will run-down significantly and FA values will go-up significantly in the enhanced regions of brain tumors after intravenous injection Gd-DTPA. It is necessary to perform DTI examination before contrast medium injection. (2) The mean ADC and rADC values are useful in the differential diagnosis of low-grade cerebral gliomas , cerebral infarctions and viral encephalitis. (3) The mean FA values and rFA values could differentiate cerebral infarctions from both low-grade cerebral gliomas and viral encephalitis. To sum up, DTI is helpful in the diagnosis and differential diagnosis between brain tumors and tumor-like lesions, and can be used as an important supplement of conventional MRI .
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