Comparison of 13N-NH3 and 18F-FDG PET/CT in the evaluation of gliomas

Abstract

Objective To investigate the diagnostic efficacy of 13N-NH3 and 18F-FDG PET/CT in the evaluation of untreated gliomas. Methods A total of 45 consecutive patients (29 males, 16 females; age range 14-75 years, average age (47.47±15.64) years) with final diagnosis of glioma from August 2009 to May 2012 were retrospectively analyzed. PET/CT imaging was performed with both 18F-FDG and 13N-NH3. Imaging results were analyzed by tumor-to-gray matter (T/G) ratios. ROC curve analysis was conducted to determine the optimal T/G cutoff values between low-grade and high-grade gliomas. One-way analysis of variance was applied to assess the differential efficacy of the two tracers in different grade of glioma. Results Forty-eight separate lesions were identified (WHO grade Ⅱ, n=16; grade Ⅲ, n=12; and grade Ⅳ, n=20). The sensitivities of 13N-NH3 PET/CT and 18F-FDG PET/CT on predicting high-grade gliomas were 91%(29/32) and 66%(21/32), respectively. The optimal T/G cutoff values for 18F-FDG and 13N-NH3 were 0.64 and 0.86 with the AUC of 0.910 and 0.943, respectively. The sensitivity and positive predictive value of predicting high-grade gliomas with optimal cutoff values were 84% (27/32) and 93% (27/29) for 18F-FDG PET/CT, those for 13N-NH3 PET/CT were 94%(30/32) and 94%(30/32), respectively. Conclusion 13N-NH3 PET/CT is superior to 18F-FDG PET/CT not only in separating low-grade gliomas from high-grade ones, but also in the detection of high-grade gliomas for better tumor to normal gray matter contrast. Key words: Glioma; Tomography, emission-computed; Tomography, X-ray computed; Nitrogen radioisotopes; NH3; Deoxyglucose