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

Abstract

PET imaging of amino acid transport using <i>O</i>-(2-¹⁸F-fluoroethyl)-l-tyrosine (¹⁸F-FET) and proton MR spectroscopy (MRS) imaging of cell turnover measured by the ratio of choline to <i>N</i>-acetyl-aspartate (Cho/NAA) may provide additional information on tumor extent of cerebral gliomas compared with anatomic imaging; however, comparative studies are rare. <b>Methods:</b> 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 ¹⁸F-FET PET and MRS imaging of Cho/NAA, determined by simultaneously acquired, 3-dimensional spatially resolved MRS imaging data, were compared. <b>Results:</b> The average tumor volumes for ¹⁸F-FET uptake and increased Cho/NAA were 19 ± 20 cm³ (mean ± SD) and 22 ± 24 cm³, 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. <b>Conclusion:</b>¹⁸F-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.