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The Combination of 13N-Ammonia and 18F-FDG in Predicting Primary Central Nervous System Lymphomas in Immunocompetent Patients

Shi, Xinchong MD; Zhang, Xiangsong PhD; Yi, Chang MD; Wang, Xiaoyan MD; Chen, Zhifeng MD; Zhang, Bing MD

doi: 10.1097/RLU.0b013e318279b6cc
Original Articles

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 13N-ammonia combined with 18F-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 18F-FDG and 13N-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 18F-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 13N-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 18F-FDG than 13N-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 13N-ammonia and 18F-FDG imaging. The combination of these 2 tracers can distinguish these 2 clinical entities effectively and make an accurate prediction of PCNSL.

From the Department of Nuclear Medicine, the First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China.

Received for publication February 23, 2012; revision accepted September 10, 2012.

Conflicts of interest and sources of funding: none declared.

Reprints: Xiangsong Zhang, PhD, Department of Nuclear Medicine, the First Affiliated Hospital of Sun Yat-Sen University, 58#, ZhongshanEr Rd, Guangzhou, China, 510080. E-mail: bdolphin@sina.cn.

© 2013 Lippincott Williams & Wilkins, Inc.