Metabolic imaging of cerebral gliomas:: Spatial correlation of changes in O-(2-18F-fluoroethyl)L-tyrosine PET and proton magnetic resonance spectroscopic imaging

The aim of this study was to determine the spatial correlation of O-(2-F-18-fluoroethyl)-L-tyrosine (F-18-FET) uptake and the concentrations of choline (Cho), creatine (Cr), and total N-acetylaspartate (tNAA) determined with proton magnetic resonance spectroscopic imaging (H-1 MRSI) in cerebral gliomas for the multimodal evaluation of metabolic changes. Methods: F-18-FET PET and 2-dimensional H-1 MRSI were performed in 15 patients with cerebral gliomas of World Health Organization (WHO) grades II-IV. PET and H-1 MRSI datasets were coregistered by use of mutual information. On the basis of their levels of F-18-FET uptake, 4 different areas in a tumor (maximum, strong, moderate, and low F-18-FET uptake) were defined on PET slices as being congruent with the volume of interest in the H-1 MRSI experiment. F-18-FET uptake in lesions was evaluated as tumor-to-brain ratios. Metabolite concentrations for Cho, Cr, and tNAA and Cho/tNAA ratios were computed for these 4 areas in the tumor and for the contralateral normal brain. Results: In the area with maximum F-18-FET uptake, the concentration of tNAA (R = -0.588) and the Cho/tNAA ratio (R = 0.945) correlated significantly with F-18-FET uptake. In the areas with strong and moderate F-18-FET uptake, only the Cho/tNAA ratios (R = 0.811 and R = 0.531, respectively) were significantly associate with amino acid transport. At low F-18-FET uptake, analysis of the correlations of amino acid uptake and metabolite concentrations yielded a significant result only for the concentration of Cr (P = 0.626). No correlation was found for metabolite concentrations determined with H-1 MRSI and F-18-FET uptake in normal brain tissue. Maximum F-18-FET uptake and the tNAA concentration were significantly different between gliomas of WHO grades II and IV, with P values of 0.032 and 0.016, respectively. Conclusion: High F-18-FET uptake, which is indicative of tumor cell infiltration, associates with neuronal cell loss (tNAA) and changes in ratios between parameters representing membrane proliferation and those of neuronal loss (Cho/tNAA ratio), which can be measured by H-1 MRSI. The significant correlation coefficients detected for Cr in regions with low F-18-FET uptake suggests an association between the mechanism governing amino acid transport and energy metabolism in areas that are infiltrated by tumor cells to a lesser extent. These findings motivate further research directed at investigating the potential of H-1 MRSI to define tumor boundaries in a manner analogous to that of amino acid PET.