Distinction between postoperative recurrent glioma and radiation injury using MR diffusion tensor imaging

This study aims to evaluate the differentiated effectiveness of MR diffusion tensor imaging (DTI) to postoperative recurrent glioma and radiation injury. Conventional MRI and DTI examination were performed using Siemens 3.0 T MR System for patients with new contrast-enhancing lesions at the site of treated tumor with postoperative radiotherapy. The region of interest was manually drawn on ADC and FA maps at contrast-enhancing lesion area, peri-lesion edema, and the contra-lateral normal white matter. Then ADC and FA values were measured and, the ADC ratio and FA ratio were calculated. Twenty patients with recurrent tumor and 15 with radiation injury were confirmed by histopathologic examination (23 patients) and clinical imaging follow-up (12 patients), respectively. The mean ADC ratio and FA ratio were compared between the two lesion types. The mean ADC ratio at contrast-enhancing lesion area was significantly lower in patients with recurrent tumor (1.34 +/- 0.15) compared to that with radiation injury (1.62 +/- 0.17; P < 0.01). The mean FA ratio at contrast-enhancing lesion area was significantly higher in patients with recurrent tumor (0.45 +/- 0.03) compared to that with radiation injury (0.32 +/- 0.03; P < 0.01). Neither mean ADC ratio nor FA ratio in edema areas had statistical difference between the two groups. A recurrent tumor was suggested when either ADC ratio < 1.65 or/and FA ratio > 0.36 at contrast-enhancing lesion area according to the receiver operating characteristics curve analysis. Three patients with recurrent tumor and two with radiation injury were misclassified. DTI is a valuable method to distinguish postoperative recurrent glioma and radiation injury.