Echo-planar spectroscopic imaging with dual-readout alternated gradients (DRAG-EPSI) at 7 T: Application for 2-hydroxyglutarate imaging in glioma patients

Magn Reson Med. 2018 Apr;79(4):1851-1861. doi: 10.1002/mrm.26884. Epub 2017 Aug 22.

Abstract

Purpose: To develop echo-planar spectroscopic imaging (EPSI) with large spectral width and accomplish high-resolution imaging of 2-hydroxyglutarate (2HG) at 7 T.

Methods: We designed a new EPSI readout scheme at 7 T. Data were recorded with dual-readout alternated gradients and combined according to the gradient polarity. Following validation of its performance in phantoms, the new readout scheme, together with previously reported 2HG-optimized magnetic resonance spectroscopy (point-resolved spectroscopy echo time of 78 ms), was used for time-efficient and high-resolution imaging of 2HG and other metabolites in five glioma patients before treatment. Unsuppressed water, acquired with EPSI, was used as reference for multichannel combination, eddy-current compensation, and metabolite quantification. Spectral fitting was conducted with the LCModel using in-house calculated basis sets.

Results: Using a readout gradient strength of 9.5 mT/m and slew rate of 90 mT/m/ms, dual-readout alternated gradients EPSI permitted 1638-Hz spectral width with 6 × 6 mm2 in-plane resolution at 7 T. Phantom data indicated that dual-readout alternated gradients EPSI provides proper metabolite signals and induces much less frequency drifts than conventional EPSI. For a spatial resolution of 0.5 mL, 2HG was detected in tumors with precision (Cramer-Rao lower bound < 10%). The 2HG was estimated to be 2.3 to 3.3 mM in tumors of three patients with biopsy-proven isocitrate dehydrogenase (IDH) mutant gliomas. The 2HG was undetectable in an IDH wild-type glioblastoma. For a radiographically suggested glioma, the estimated 2HG of 2.3 ± 0.2 mM (Cramer-Rao lower bound < 10%) indicated that the lesion may be an IDH mutant glioma.

Conclusions: The data indicated that the dual-readout alternated gradients EPSI can provide reliable high-resolution imaging of 2HG in glioma patients at 7 T in vivo. Magn Reson Med 79:1851-1861, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Keywords: 1H MRS; 2-hydroxyglutarate (2HG); 7T; dual-readout alternated-gradients EPSI (DRAG-EPSI); echo-planar spectroscopy imaging (EPSI); glioma; human brain tumor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Biomarkers
  • Brain Neoplasms / diagnostic imaging*
  • Brain Neoplasms / genetics
  • Echo-Planar Imaging / methods*
  • Female
  • Glioma / diagnostic imaging*
  • Glioma / genetics
  • Glutarates / chemistry*
  • Humans
  • Image Processing, Computer-Assisted / methods
  • Isocitrate Dehydrogenase / genetics
  • Magnetic Resonance Spectroscopy / methods*
  • Male
  • Middle Aged
  • Mutation
  • Oligodendroglioma / diagnostic imaging
  • Oligodendroglioma / genetics
  • Phantoms, Imaging

Substances

  • Biomarkers
  • Glutarates
  • alpha-hydroxyglutarate
  • Isocitrate Dehydrogenase