Diffusion Tensor Imaging of High-Grade Astrocytomas

Objective:To evaluate the usefulness of FA and ADC in differentiating tumor,edema area,and normal white matter.Methods:16 patients with pathological grade Ⅲ～Ⅳ astrocytomas underwent conventional MR and DTI before therapy.Tumor,edema and apparent normal white matter regions of brain were determined on T 2WI and contrast-enhanced T 1WI images.Apparent diffusion coefficients (ADC) value and fractional anisotropy (FA) value were calculated in areas of tumor,edema,and normal brain.Comparisons were made by analysis of each variance.Results:On ADC map,the tumors were almost isointense compared with the normal brain,and the edematous brain was slightly hyperintense than the normal brain;necrotic tumor core showed high signal.On FA map,the necrotic tumor core appeared hypointense,the tumor appeared isointense or hypointense,the edematous brain appeared isointense or slightly hyperintense.The ADC value was the highest in the necrotic tumor core(2.16±0.147)×10 -3 mm 2/s,followed by edematous brain(1.55 ±0.066)×10 -3 mm 2/s,enhancing tumor tissue(1.33 ±0.08)×10 -3 mm 2/s,and normal white matter (0.76±0.057)×10 -3 mm 2/s.FA was the lowest in the necrotic core (0.05±0.012) and was the highest in normal white matter (0.45±0.037).ADC was significantly different in enhancing tumor,necrotic tumor core,edematous and normal white matter in all patients.FA was significantly different in tumor solid area,necrotic tumor core and normal white matter in all cases.There was no significant difference of FA value between tumor and edematous brain on FA map.Conclusion:ADC value can help to distinguish tumor from adjacent edema,necrotic tumor core and normal white matter.FA value added no benefit to differentiation diagnosis.Further study are needed to confirm whether ADC value and FA value can be used to differentiate tumor invasion.