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

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.

• Authors: Zhongxu An, Vivek Tiwari, Sandeep K Ganji, Jeannie Baxter, Michael Levy, Marco C Pinho, Edward Pan, Elizabeth A Maher, Toral R Patel, Bruce E Mickey, Changho Choi
• Journal: Magnetic resonance in medicine (Magn Reson Med) Vol. 79 Issue 4 Pg. 1851-1861 (04 2018) ISSN: 1522-2594 [Electronic] United States
• PMID: 28833542 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: © 2017 International Society for Magnetic Resonance in Medicine.

Chemical References

• Biomarkers
• Glutarates
• alpha-hydroxyglutarate
• Isocitrate Dehydrogenase

Topics

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