^13N—NH3 PET显像评价^18F-FDG PET示低代谢脑内病变的应用价值

Application of ^13N-NH3 PET in the evaluation of hypometabolic brain lesions on ^18F-FDG PET

目的探讨^13N-NH3 PET显像在^18F-FDG PET显像呈低代谢表现的脑内病变中的应用价值。方法对18例”F—FDGPET显像呈低代谢表现的脑内病变患者[男13例，女5例，年龄20—68（42．4±12．6）岁]进行^13N-NH3 PET显像前瞻性研究。2种显像间隔时间在10d内，间隔时间内患者未接受任何治疗。18例患者中，初诊14例，星形细胞瘤治疗后复诊患者4例；最后经病理（13例）、临床随访（5例）证实有神经胶质瘤10例，肺癌脑转移1例，胚胎发育不良性神经上皮瘤（DNT）1例和非肿瘤性病变6例（3例放射性坏死，2例脑炎，1例脑缺血病变）。采用对称ROI法计算2种显像肿瘤与对侧正常脑组织放射性比值（T／C）。计算^13N-NH3 PET诊断效能。应用SPSS13．0软件对^13N—NH3和^18F—FDG的T／C行配对t检验，对肿瘤性病变与非肿瘤性病变中^13N—NH3的T／C行两样本t检验。结果12例肿瘤性病变中，7例表现为^13N—NH3摄取增高（星形细胞瘤5例，胶质母细胞瘤2例），诊断灵敏度为58％（7／12）；3例低级别的胶质瘤、1例转移瘤及1例DNT表现为^13N—NH3摄取减低。在肿瘤性病变中，^13N-NH3的T／C明显高于^18F-FDG（1．24±0．66和0．67±0．24，t=-3．740，P〈0．05）。6例非肿瘤性病变均表现为^13N-NH3摄取减低，特异性为6／6。在非肿瘤性病变中，^18F—FDG和^13N—NH3的T／C分别为0．68±0．15和0．70±0．19，两者间差异无统计学意义（t=-0．246，P〉0．05）。肿瘤性病变的^13N-NH3 T／C明显高于非肿瘤性病变（1．24±0．53和0．70±0．19，t=2．624，P〈0．05）。结论在^18F—FDG PET显像呈低代谢的脑内病变（尤其是星形细胞瘤）的诊断与鉴别诊断中，^13N-NH3 PET显像具有很高的特异性，但其灵敏度有待进一步提高。

Objective To investigate the usefulness of 13N-NH3 PET in detecting brain lesions which show hypometabolism on is F-FDG PET. Methods 13 N-NH3 PET imaging was performed for a prospective study in 18 patients with brain lesions that showed hypometabolism compared with normal brain tissue on 18 F-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 le- sions （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-contra- lateral brain tissue ratios （T/C） were calculated by the ROI method. The diagnostic efficacy of 13 N.NH3 PET was evaluated. Paired t test and two-sample t test were performed to analyze the differences of T/C be- tween different groups. Results Seven （5 astrocytomas and 2 glioblastomas） of 12 brain tumors （ sensitivi- ty： 58%, 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 ^18F-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 13 N-NH3 uptake （specificity： 6/6）. The T/C ratios of 18 F-FDG and ^13NNH3 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 13 N-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 ^18F-FDG PET imaging from non-neoplastic lesions with high specificity, especially for cerebral astrocytomas, but the sensitivity is relatively limited.