• Bangkim C Khangembam, Punit Sharma, Sellam Karunanithi, Abhinav Singhal, Chandan J Das, Praveen Kumar, Pramod K Julka, Guru P Bandopadhyaya, Rakesh Kumar, Arun Malhotra, and Chandrasekhar Bal.
• Departments of aNuclear Medicine bRadiodiagnosis cRadiation Oncology, All India Institute of Medical Sciences, New Delhi, India.
• Nucl Med Commun. 2013 Nov 1; 34 (11): 1046-54.

PurposeWe assessed the value of N-ammonia PET-computed tomography (PET/CT) in recurrent glioma and compared the results with those of contrast-enhanced MRI (CE MRI).Materials And MethodsFifty-two (mean age, 39.8±11.6 years; male, 33; female, 19) histopathologically proven and previously treated glioma patients with clinical suspicion of recurrence were evaluated with 13N-ammonia PET/CT and CE MRI. PET/CT images were evaluated qualitatively and quantitatively (maximum standardized uptake value). Tumour to white matter (T/W), tumour to grey matter (T/G) and tumour to pituitary (T/P) ratios were calculated and cutoff levels were derived with receiver operating characteristic curve analysis. Sensitivity, specificity and predictive values were compared. A combination of clinical follow-up, repeat imaging and biopsy (when available) was taken as the reference standard.ResultsOn the basis of the reference standard, 23 out of 52 patients were seen to have recurrence. Overall sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 13N-ammonia PET/CT were 82.6, 86.2, 82.6, 86.2 and 84.6%, respectively, whereas those of CE MRI were 96.7, 48.3, 59.5, 93.3 and 69.2%, respectively. Overall, 13N-ammonia PET/CT was statistically superior to CE MRI (P=0.001). In low-grade tumours, 13N-ammonia PET/CT performed better than MRI with an accuracy of 86.8 versus 68.4% (P=0.003). In high-grade tumours, both the modalities had comparable performances with accuracies of 78.6% for N-ammonia PET/CT and 71.4% for CE MRI (P=0.250). Among the ratios, T/P was the most useful, with the largest area under the curve (0.825; P=0.0001).ConclusionN-Ammonia PET/CT shows higher accuracy compared with contrast-enhanced MRI for detecting recurrent gliomas, particularly in low-grade tumours.

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