Diffusion tensor imaging and 1H-MRS study on radiation-induced brain injury after nasopharyngeal carcinoma radiotherapy

Aim: To investigate the metabolic characteristics of the temporal lobes following radiation therapy for nasopharyngeal carcinoma using diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (1H-MRS). Materials and methods: DTI and 1H-MRS were performed in 48 patients after radiotherapy for nasopharyngeal carcinoma and in 24 healthy, age-matched controls. All patients and controls had normal findings on conventional MRI. Apparent diffusion coefficient (ADC), fractional anisotropy (FA), three eigenvalues λ1, λ2, λ3, N-acetylaspartic acid (NAA)/choline (Cho), NAA/creatinine (Cr), and Cho/Cr were measured in both temporal lobes. Patients were divided into three groups according to time after completion of radiotherapy: group 1, less than 6 months; group 2, 6–12 months; group 3, more than 12 months. Mean values for each parameter were compared using one-way analysis of variance (ANOVA). Results: Mean FA in group 1 was significantly lower compared to group 3 and the control group (p < 0.05). Group-wise comparisons of apparent diffusion coefficient (ADC) values among all the groups were not significantly different. Eigenvalue λ1 was significantly lower in groups 1 and 3 compared to the control group (p < 0.05). NAA/Cho and NAA/Cr were significantly lower in each group compared to the control group (p < 0.01 for both). The decrease in NAA/Cho was greatest in group 1. There were no significant between-group differences regarding Cho/Cr. Conclusion: A combination of DTI and 1H-MRS can be used to detect radiation-induced brain injury, in patients treated for nasopharyngeal carcinoma.