Objective: Both 18F-FDG PET and perfusion MRI are commonly used techniques for posttreatment glioma surveillance. Using integrated PET-MRI, we assessed the rate of discordance between simultaneously acquired FDG PET images and dynamic contrast-enhanced (DCE) perfusion MR images and determined whether tumor genetics predicts discordance.
Materials and methods: Forty-one consecutive patients with high-grade gliomas (20 with grade IV gliomas and 21 with grade III gliomas) underwent a standardized tumor protocol performed using an integrated 3-T PET-MRI scanner. Quantitative measures of standardized uptake value, plasma volume, and permeability were obtained from segmented whole-tumor volumes of interest and targeted ROIs. ROC curve analysis and the Youden index were used to identify optimal cutoffs for FDG PET and DCE-MRI. Two-by-two contingency tables and percent agreement were used to assess accuracy and concordance. Twenty-six patients (63%) from the cohort underwent next-generation sequencing for tumor genetics.
Results: The best-performing FDG PET and DCE-MRI cutoffs achieved sensitivities of 94% and 91%, respectively; specificities of 56% and 89%, respectively; and accuracies of 80% and 83%, respectively. FDG PET and DCE-MRI findings were discordant for 11 patients (27%), with DCE-MRI findings correct for six of these patients (55%). Tumor grade, tumor volume, bevacizumab exposure, and time since radiation predicted discordance between FDG PET and DCE-MRI findings, with an ROC AUC value of 0.78. Isocitrate dehydrogenase gene and receptor tyrosine kinase gene pathway mutations increased the ROC AUC value to 0.83.
Conclusion: FDG PET and DCE-MRI show comparable accuracy and sensitivity in identifying tumor progression. These modalities were shown to have discordant findings for more than a quarter of the patients assessed. Tumor genetics may contribute to perfusion-metabolism discordance, warranting further investigation.
Keywords: PET-MRI; glioma; perfusion; permeability; tumor.