Proton magnetic resonance spectroscopy for radiation encephalopathy induced by radiotherapy for nasopharyngeal carcinoma.

OBJECTIVE: To understand the metabolic patterns of NAA, Cr and Cho in radiation encephalopathy (RE) induced by radiotherapy for nasopharyngeal carcinoma detected by proton magnetic resonance spectroscopy (1H-MRS), and provide useful evidence for early diagnosis of this disease. METHODS: Chemical shift imaging 1H-MRS was performed for 10 healthy volunteers (control group) and 21 patients with pathologically confirmed nasopharyngeal carcinomas, who developed RE after radical radiotherapy as diagnosed on the basis of clinical symptoms and imaging findings. The contents of NAA, Cr and Cho in the pixels were observed, the metabolic maps generated, and NAA/Cr and NAA/Cho ratios calculated for all the subjects. RESULTS: The concentrations of NAA, Cr and Cho were rarely observed in the necrosis and liquefaction foci in the patients, nor were any signals displayed on their metabolic maps. In the visible lesions, with the exception of the necrosis and liquefaction foci, the content of NAA increased slightly, whereas that of Cr or Cho decreased obviously or even became absent. An area around the lesion was identified where NAA content decreased but Cr or Cho increased. The signal in the metabolic maps appeared indistinguishable. The NAA/Cr and NAA/Cho ratios were less than 1. Farther away from the visible lesions, the NAA, Cr and Cho contents remained normal with NAA/Cr and NAA/Cho ratios of less than 1. CONCLUSION: 1H-MRS is capable of displaying the patterns of metabolite changes in RE induced by radiotherapy, and identifying larger area of abnormal metabolism in RE than the visible lesion in MRI, which suggests the possibility of earlier detection of RE with 1H-MRS.