Multiparametric evaluation of low grade gliomas at follow-up: comparison between diffusion and perfusion MR with 18F-FDOPA PET

Objective: To compare MRI using perfusion and diffusion techniques with 6-[F-18]-fluoro-L-3,4-dihydroxyphenylalanine (F-18-FDOPA) positron emission tomography (PET) in the follow-up of low-grade gliomas (LGGs) and to identify the best imaging parameter to differentiate patients with different prognosis. Methods: Between 2010 and 2015, 12 patients with a pathology-proven diagnosis of LGG and MR (with perfusion and diffusion sequences) and a PET study during their follow-up were retrospectively included in our study. Cerebral blood volume (CBV) and apparent diffusion coefficient (ADC) maps on MR studies and PET images were evaluated using a region of interest-based method. All patients were categorized as stable or as having progressive disease at 1-year follow-up. Statistical analysis was performed using Pearson's correlation test and multivariate analysis of variance (p, 0.05). Results: No significant correlations were found between PET parameters [maximum tumour-to-controlateral normal brain ratio (T/N-max) and tumour-to-striatum ratio] and ADC or relative CBV values measured in both PET hotspot regions and areas of maximum signal alterations. T/Nmax demonstrated a good sensitivity (83%) and specificity (100%) for differentiating two subgroups of patients with different outcomes at 1-year-follow-up (p, 0.05). Conclusion: Perfusion and diffusion MR images provide different information compared with F-18-FDOPA PET in LGGs during follow-up and therefore, they should be considered as complementary tools in the evaluation of these tumours. F-18-FDOPA PET showed a significant prognostic role in the follow-up of LGGs and appeared to be a better tool than MR advanced techniques for outcome prediction. These results need to be confirmed with longitudinal studies on a larger population. Advances in knowledge: This is the first study that compared F-18-FDOPA PET with perfusion and diffusion MR in LGGs during follow-up. These preliminary results highlight the importance of a multimodality approach in this field and evidence a potential role for F-18-FDOPA PET to predict patients at risk for tumour progression.