Diffusion tensor imaging and 1H-MR spectroscopy study on radiation-induced injury of the brain after nasopharyngeal carcinoma radiotherapy

Abstract

Objective To investigate the changes of brain tissue in bilateral temporal lobes at different stages after nasopharyngeal carcinoma radiotherapy by diffusion tensor imaging(DTI)and 1H-MR spectroscopy(1H-MRS).Methods DTI and 1H-MRS were performed in 48 patients with nasopharyngeal carcinoma.in which conventional MRI revealed normal findings after radiotherapy.Twenty-four healthy controls were enrolled in this study and underwent the galne MR scanning.After the image processing and spectral analysis,apparent diffusion coefficient(ADC),fractional anisotropy(FA) and 3 eigenvalue λ1,λ2,λ3 of DTI and the NAA/Cho,NAA/Cr,Cho/Cr of 1H-MRS were measured in bilateral temporal lobes.Forty-eight NPC patients were divided into 3 groups [ less than 6 months(16 cases),6 to 12 months (6 cases)and more than 12 months(26 cases)after radiotherapy]according to different stages of radiationinduced injury of brain.each group's DTI and 1H-MRS data were measured respectively and one-way ANOVA was applied to analyze each parameter. Results The FA value of each test group(less than 6 months.6 to 12 months and more than 12 months)and the control group were 0.445±0.017,0.460±0.016,0.461±0.025,0.473±0.023 respectively.The ADC values of each group were(8.51±0.43)×10-4.(8.48±0.34)×10-4,(8.40±0.33)×10-4,(8.68±0.57)×10-4mm2/s respectively.And the maximum eigenvalue λ1 of each group were(1.251±0.065)× 10-3,(1.293±0.051)×10-3,(1.317±0.074)×10-3,(1.350±0.091)× 10-3mm2/s.The three indicators were significantly difrerent among groups(F=10.873,3.399,9.750 respectively,P<0.05).λ2,λ3 values showed no significant difference among the groups.The NAA/Cho of 1H-MRS of each groups were0.910±0.112,0.972±0.101,1.060±0.095,1.261±0.105 respectively,and the NAA/Cr were 1.212±0.236,1.208±0.183,1.228±0.236,1.435±0.225 respectively.Both of them had significant differences among groups(F=52.840,8.176 respectively,P<0.01).Cho/Cr showed no significant difference among the groups.Conclusions DTI combining with 1H-MRS play a certain guiding role on monitoring and evaluating of radiation injury of brain tissue in nasopharyngeal carcinoma after radiotherapy.It Can provide a scientific basis for the dynamic monitoring of radiation brain injury. Key words: Nasopharyngeal neoplasms; Radiation injuries; Diffusion magnetic resonance imaging; Magnetic resonance spectroscopy