The Applicative Value Of MR Diffusion Weighted Imaging In The Diagnosis Of Cerebral Astrocytic Tumors

Objective To explore the applicative value of MR diffusion weighted imaging in the diagnosis of cerebral astrocytic tumors ,incuding the tumorous showing,pathological grading, peritumoral infiltration, postoperated recurrence of tumors. Materials and Methods The study object is the 56 patients who were diagnosed as cerebral astrocytic tumors between june 2003 and January 2005 in our hospital.The 29 of 56 patients were followed up to make sure the tumors would be recurrence or not by MRI examination. All patients were examined with a 1.5-T MR unit (Signa; GE Medical Systems) by using a circularly polarized head coils. The routine MR imaging included the axial T2-weighted fast spin-echo , axial T1-weighted spin-echo and sagittal T1-weighted spin-echo sequences before contrast enhancement. Diffusion weighted imagings were performed in the transverse plane by using a spin-echo echo-planar imaging sequence, diffusion gradient encoding in three orthogonal directions applied in the x, y, and z directions;b = 0 sec/mm2 and b = 1,000 sec/mm2. Apparent Diffusion Coefficient (ADC) and Exponent Diffusion Coefficient(EDC) maps were generated with software (Functool2; GE Medical Systems). Combined with conventional MR imaging, the ROIs, which had been used to measure the ADC and EDC values, were placed in the tumoral core, cystic region, necrotic region, peritumoral edematous region, peritumoral normal-appearing white matter and contralateral white matter. Relative ADC(rADC)and relative EDC(rEDC) were calculated too. The relationship between tumor grade and the diffusion-measurement-value of tumoral core, peritumoral edema and normal-appearing white matter were analyzed,but also the relationship between tumor recurrence and peritumoral rADC or rEDC value of peritumoral edema and normal-appearing white matter were analyzed.SPSS for 11.0 statistical software package was used to assess the dfference of difference regions. the two-sample t test was used for statistical analysis, and for comparisons between peritumoral normal-appearing white matter and contralateral white matter, a paired t test was used. A P value of less than 0.05 was considered to represent a statistically significant difference in all cases. Results This group of 56 cerebral astrocytic tumors were verified by histology,incuding 2 pilocytic astrocytoma(grade Ⅰ),33 astrocytoma(grade Ⅱ),8 anaplastic astrocytoma(grade Ⅲ),13 glioblastoma multiforme(grade Ⅳ). According to ADC and rADC value of the tumor core, it was the highest in low grade astrocytoma, followed by anaplastic astrocytoma and glioblastoma multiforme ;the EDC and rEDC value of the tumor core were reverse order.Significant differences of ADC and EDC values were found between low grade astrocytoma and anaplastic astrocytoma, but not between anaplastic astrocytoma and glioblastoma multiforme. Significant differences of rADC and rEDC values were found between three group tumors , but there were more overlap between anaplastic astrocytoma and glioblastoma multiforme. The accuracy was the highest When rADC value was 1.53 as a threshold value between low and high astrocytic tumors ,the overall accuracy rate was 89.3%,the underestimating rate was 4.78%,the overestimating rate was 14.3%. There was no significant difference between three group tumors in peritumora diffusion values. The ADC value (0.80±0.09) was higher in the peritumoral normal-appearing white matter regions than in the normal-appearing contralateral white matter regions (0.76±0.08), The EDC value(0.45±0.04) was lower in the peritumoral normal-appearing white matter regions than in the normal-appearing contralateral white matter regions(0.47±0.03) . 9 of 22 followed-up patients were nonrecurrence,include 8 low grade astrocytomas and 1 anaplastic astrocytoma; there were 13 recurrence in the 22 followed-uppatients,include 5 low grade astrocytomas , 1 anaplastic astrocytoma and 7 glioblastoma multiforme.The overall recurrence rate of low grade astrocytomas which have not peritumoral edema was 30%.The rADC value of nonrecurrence group in peritu...