Application of 13N-NH3 PET in the evaluation of hypometabolic brain lesions on 18F-FDG PET / 中华核医学与分子影像杂志

ABSTRACT

Objective To investigate the usefulness of 13N-NH3 PET in detecting brain lesions which show hypometabolism on 18F-FDG PET.Methods 13N-NH3 PET imaging was performed for a prospective study in 18 patients with brain lesions that showed hypometabolism compared with normal brain tissue on 18F-FDG PET scans.Fourteen patients underwent 18 F-FDG PET imaging for initial diagnosis and 4 patients for detection of astrocytoma recurrence (13 males,5 females,age 20-68 (42.4 ± 12.6) years).Ten gliomas,1 metastatic tumor,1 dysembryoplastic neuroepithelial tumor (DNT) and 6 non-neoplastic lesions (including 3 cases of radiation necrosis,2 cases of encephalitic foci,and 1 case of ischemic lesion)were verified by histopathological examination (n =13) or clinical follow-up (n =5).The tumor-to-contralateral brain tissue ratios (T/C) were calculated by the ROI method.The diagnostic efficacy of 13N-NH3 PET was evaluated.Paired t test and two-sample t test were performed to analyze the differences of T/C between different groups.Results Seven (5 astrocytomas and 2 glioblastomas) of 12 brain tumors (sensitivity58％,7/12) showed increased 13N-NH3 uptake (higher uptake than the contralateral brain tissue),while 3 low-grade gliomas,1 metastatic tumor,and 1 DNT showed decreased 13N-NH3 uptake (no uptake or lower uptake than the contralateral brain tissue).The uptake ratio of 13N-NH3 was significantly higher than that of 18 F-FDG (1.24 ± 0.66 vs 0.67 ± 0.24,t =-3.740,P ＜ 0.05) in the tumors.All six non-neoplastic lesions showed decreased 13N-NH3 uptake (specificity6/6).The T/C ratios of 18F-FDG and 13N-NH3 in the non-neoplastic lesions were 0.68 ±0.15 and 0.70 ±0.19,respectively,and there was no significant difference between them (t =-0.246,P ＞ 0.05).The T/C ratio of 13N-NH3 in the tumors was significantly higher than that in the non-neoplastic lesions (1.24 ± 0.53 vs 0.70 ± 0.19,t =2.624,P ＜ 0.05).Conclusion 13N-NH3 PET imaging may be helpful to detect and differentiate brain tumors with hypometabolism as detected by 18 F-FDG PET imaging from non-neoplastic lesions with high specificity,especially for cerebral astrocytomas,but the sensitivity is relatively limited.