Spatial Relationship of Glioma Volume Derived from 18F-FET PET and Volumetric MR Spectroscopy Imaging: A Hybrid PET/MRI Study

PET imaging of amino acid transport using O-(2-F-18-fluoroethyl)-L-tyrosine (F-18-FET) and proton MR spectroscopy (MRS) imaging of cell turnover measured by the ratio of choline to N-acetyl-aspartate (Cho/NAA) may provide additional information on tumor extent of cerebral gliomas compared with anatomic imaging; however, comparative studies are rare. Methods: In this prospective study, 41 patients (16 women, 25 men; mean age +/- SD, 48 +/- 14 y) with cerebral gliomas (World Health Organization [WHO] grade II: 10 [including 1 patient with 2 lesions], WHO III: 17, WHO IV: 13, without biopsy low-grade: 1, high-grade: 1) were investigated with a hybrid PET/MR scanner. Tumor extent, spatial overlap, and the distance between the corresponding centers of mass in F-18-FET PET and MRS imaging of Cho/NAA, determined by simultaneously acquired, 3-dimensional spatially resolved MRS imaging data, were compared. Results: The average tumor volumes for F-18-FET uptake and increased Cho/NAA were 19 +/- 20 cm(3) (mean +/- SD) and 22 +/- 24 cm(3), respectively, with an overlap of 40% +/- 25% and separation of the centers of mass by 9 +/- 8 mm. None of the parameters showed a significant correlation with tumor grade. Conclusion: F-18-FET uptake and increased Cho/NAA ratio are not always congruent and may represent different properties of glioma metabolism. The relationship to histologic tumor extent needs to be further analyzed.