Accuracy of 2-hydroxyglutarate quantification by short-echo proton-MRS at 3 T: A phantom study

Purpose: We set out to investigate the potential confounding effect of variable concentration of N-acetyl. l-aspartate (NAA) and Glutamate (Glu) on measurement of the brain oncometabolite 2-hydroxyglutarate (2HG) using a standard MRS protocol. This issue may arise due to spectral overlap at clinical magnetic field strengths and thus complicate the usage of 2HG as a putative biomarker of gliomas bearing mutations of the isocitrate dehydrogenase (IDH) 1 and 2 genes. Methods: Spectra from 25 phantoms (50mL falcon test tubes) containing a range of known concentrations of 2HG, NAA and Glu were acquired using a clinical 3T scanner with a quadrature head coil, single-voxel point-resolved spectroscopy sequence with TE=30ms. Metabolite concentrations were estimated by linear combination analysis and a simulated basis set. Results: NAA and Glu concentrations can have a significant confounding effect on 2HG measurements, whereby the negative changes in concentration of these metabolites typically observed in (peri)lesional areas can lead to under-estimation of 2HG concentration with respect to spectra acquired in presence of physiological levels of NAA and Glu. Conclusion: The confounding effect of NAA and Glu concentration changes needs to be considered: in patients, it may mask the presence of 2HG at low concentrations, however it is not expected to lead to false positives. 2HG data acquired using standard short echo-time MRS protocols should be considered with caution.