[Validation of MRI and 18F-FDG-PET coregistration in patients with primary brain tumors]

To evaluate the role of PET and MRI fused image study inpatients with primary brain tumors previously treated, to determine the presence of radionecrosis vs residual tumor viability.

Primary brain tumors were diagnosed by biopse and MR. 18FDG-PET scan and T1 enhanced MRI follow-up studies were performed between 3 and 5 months after treatment. The 18F-FDG uptake was semiquantitavively calculated by a region-of-interest based Tumor hotspot/normal brain tissue index.

Fifty-seven patients were studied, 37 had high grade gliomas; 9 had oligoastrocytomas; 5 had Embrionary tumors; I had a meningyoma and I had an oliodendroglial tumor. All MR studies showed tumor enhancement, without determine wether if it was radionecrosis or tumor viability. PET/MR fused study diagnosed 21 negative studies (30%) and 36 positive results (70%). Tumor hotspot/normal brain tissue index correlated well with the visual analysis registered.

Visual analysis in the contrast enhanced MR overestimates the tumoral area, without defining a possible diagnosis between tumor viability and radionecrosis. Metabolic activity in the 18F-FDG PET study in the enhanced area, determines the presence of residual tumor viability. Therefore, coregistration can be used to obtain a more specific diagnosis optimizing the cinical use.