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-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) uptake and the concentrations of choline (Cho), creatine (Cr), and total N-acetylaspartate (tNAA) determined with proton magnetic resonance spectroscopic imaging ((1)H MRSI) in cerebral gliomas for the multimodal evaluation of metabolic changes.


METHODS
(18)F-FET PET and 2-dimensional (1)H MRSI were performed in 15 patients with cerebral gliomas of World Health Organization (WHO) grades II-IV. PET and (1)H MRSI datasets were coregistered by use of mutual information. On the basis of their levels of (18)F-FET uptake, 4 different areas in a tumor (maximum, strong, moderate, and low (18)F-FET uptake) were defined on PET slices as being congruent with the volume of interest in the (1)H MRSI experiment. (18)F-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 (18)F-FET uptake, the concentration of tNAA (R= -0.588) and the Cho/tNAA ratio (R=0.945) correlated significantly with (18)F-FET uptake. In the areas with strong and moderate (18)F-FET uptake, only the Cho/tNAA ratios (R=0.811 and R=0.531, respectively) were significantly associated with amino acid transport. At low (18)F-FET uptake, analysis of the correlations of amino acid uptake and metabolite concentrations yielded a significant result only for the concentration of Cr (R=0.626). No correlation was found for metabolite concentrations determined with (1)H MRSI and (18)F-FET uptake in normal brain tissue. Maximum (18)F-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.


CONCLUSIONS
High (18)F-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 (1)H MRSI. The significant correlation coefficients detected for Cr in regions with low (18)F-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 (1)H MRSI to define tumor boundaries in a manner analogous to that of amino acid PET.
Stadlbauer
Andreas
A
Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen, Germany. andi@nmr.at
Prante
Olaf
O
Nimsky
Christopher
C
Salomonowitz
Erich
E
Buchfelder
Michael
M
Kuwert
Torsten
T
Linke
Rainer
R
Ganslandt
Oliver
O
D000328:Adult; D000368:Aged; D002462:Cell Membrane / Q000378:metabolism; D054022:Cerebrum / Q000378:metabolism / Q000473:pathology*; D004734:Energy Metabolism; D005260:Female; D005910:Glioma / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods*; D011522:Protons; D014443:Tyrosine / Q000031:analogs & derivatives*
C117289:O-(2-fluoroethyl)tyrosine; D011522:Protons; D014443:Tyrosine