title: The combination of 13N-ammonia and 18F-FDG in predicting primary central nervous system lymphomas in immunocompetent patients.
abstract: OBJECTIVE
  Accurate identification of primary central nervous system lymphoma (PCNSL) and its differentiation from other brain tumors remain difficult but are essential for treatment. In this study, we investigated whether (13)N-ammonia combined with (18)F-FDG could distinguish PCNSL from solid gliomas effectively.
  
  
  METHODS
  Ten consecutive patients with final diagnosis of PCNSL (5 female and 5 male patients; mean [SD] age, 59.10 [12.47] years; range, 43-74 years) and another fifteen consecutive patients with solid glioma lesions (5 female and 10 male patients; mean [SD] age, 46.73 [19.61] years; range, 14-72 years) were included in this study. PET/CT imaging was performed for all of them with both (18)F-FDG and (13)N-ammonia as tracers. Tumor-to-gray matter (T/G) ratios were calculated for the evaluation of tumor uptake. Both Student t test and discriminant analysis were recruited to assess the differential efficacy of these 2 tracers.
  
  
  RESULTS
  The T/G ratios of (18)F-FDG in PCNSL lesions were higher than in solid gliomas (3.26 [1.18] vs 1.56 [0.41], P < 0.001), whereas the T/G ratios of (13)N-ammonia in PCNSL lesions were lower than in solid gliomas significantly (1.38 [0.20] vs 2.11 [0.69], P < 0.001). All the lesions of PCNSL displayed higher T/G ratios of (18)F-FDG than (13)N-ammonia, whereas 14 (77.8%) of 18 glioma lesions showed contrary results. Tumor classification by means of canonical discriminant analysis yielded an overall accuracy of 96.9%, and only one glioma lesion was misclassified into the PCNSL group.
  
  
  CONCLUSIONS
  PCNSLs and solid gliomas have different metabolic profiles on N-ammonia and F-FDG imaging. The combination of these 2 tracers can distinguish these 2 clinical entities effectively and make an accurate prediction of PCNSL.
authors: Department of Nuclear Medicine, the First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China. bdolphin@sina.cn
authors: Xinchong
authors: X
authors: Shi
authors: Xiangsong
authors: X
authors: Zhang
authors: Chang
authors: C
authors: Yi
authors: Xiaoyan
authors: X
authors: Wang
authors: Zhifeng
authors: Z
authors: Chen
authors: Bing
authors: B
authors: Zhang
mesh_terms: D000328:Adult; D000368:Aged; D000641:Ammonia; D016543:Central Nervous System Neoplasms / Q000000981:diagnostic imaging* / Q000276:immunology*; D003937:Diagnosis, Differential; D005260:Female; D019788:Fluorodeoxyglucose F18; D005909:Glioblastoma / Q000000981:diagnostic imaging; D006801:Humans; D007121:Immunocompetence; D008223:Lymphoma / Q000000981:diagnostic imaging* / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009590:Nitrogen Radioisotopes; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D009590:Nitrogen Radioisotopes; D019788:Fluorodeoxyglucose F18; D000641:Ammonia