The Values Of MR Diffusion-weighted Imaging In The Diagnosis Of The Cerebral Astrocytic Tumors

objective:To evaluate the usefulness of diffusion-weighted imaging (DWI)and apparent diffusion coefficients(ADC) in the diagnosis of cerebral astrocytic tumors.Materials and Methods: Using a 1.5-T superconducting MR unit(Magnetom Symphony;Siemens,Germany),Forty pathologically confirmed cerebral astrocytic tumors underwent conventional T1-weighted imaging, T2-weighted imaging, contrast-enhanced MR imaging and diffusion-weighted imaging,we used two different b values(b=0s/mm2 and b=1000s/mm2).In the normal group,We calculated ADC values and ADC maps values of normal ganglion basilare,cerebral cortex,brain white matter and CSF,In the abnormal group,we calculated ADC values and ADC maps values of tumorous areas,necrotic or cystic areas of tumors and surrounding edematous areas,The coefficient of variation (CV) of benign tumors and malignant tumors were measured and computed with toolbar(Freehand) of MR unit, ADC values of every direction(read,phase,slice,3trace) were calculated in brain ganglion basilare,cerebral cortex,brain white matter and astrocytic tumors,statistical significance was determined using one-way ANOVA or t test to compare them.In 40 cases,tumor cellularity of tumorous areas was computed with imaging anlaysis software, At the same time, ADC values of tumorous areas were measured in corresponding areas, statistical comparisons of the ADC values with tumor cellularity were made linear regresion analysis and Pearson`s correlation coefficient.Results: 40 astrocytic tumors with pathologically-proved brain tumor included pilocytic astrocytomas (n=7),astrocytomas(n=13) ,anaplastic astrocytomas (n=9), glioblastoma multiformes (n=11).In our study, the apparent diffusion coefficient values of the normal group had significantly different from that of the abnormal group (F=253.643,P<0.001),In abnormal group,A significant difference was found between the ADC values of tumorous areas and tumorous necrotic or cystic areas (P<0.01),between the ADC values of edematous areas and tumorous necrotic or cystic areas (P<0.05),between the ADC values of malignant tumorous areas and surrounding edematous areas (P<0.05),but not between benign tumorous areas and surrounding edematous areas(P>0.05). The CV of benign tumorous ADC values was statistically different from that of malignant tumorous ADC values, significant difference existed among the ADC values of read ,slice,phase directions in brain white matter(P<0.05),but not among in cerebral cortex,in ganglion basilare and in astrocytic tumors(P>0.05).The ADC values were inversely correlated with tumor cellularity,pearson`s correlation coefficient was –0.848.Conclusion: Measuring ADC values enabled us to differentiate various components of the tumor (e.g. tumorous portion,cystic or necrotic portion,surrounding edematous portion )and normal tissue;ADC values and CV of ADC values had great clinical value in distinguishing benign tumor from malignant tumor；In brain white matter,diffusion is anisotropic,in cerebral cortex and ganglion basilare,diffusion is isotropic,in astrocytic tumors, diffusion had the characterization of isotropic；Tumor cellularity was higher,ADC value was lower, vice verse.Benign tumor cellularity was low,mean ADC values were high, malignant tumorous cells reproducted rapidly and tumor cellularity was high,ADC values were low.Diffusion-weighted imaging can be used to evaluate the ways of tumorous reproduction. In addition,cerebral diffusion- weighted imaging played a important role in differentiating astrocytic tumors from acute ischemic stroke,brain abscesses, brain matastasis and recurrent astrocytomas.