Gamma-aminobutyric acid (GABA) and glutamate (Glu) are the major neurotransmitters in the brain. They are crucial for the functioning of healthy brain and their alteration is a major mechanism in the pathophysiology of many neuro-psychiatric disorders.Magnetic resonance spectroscopy (MRS) is the only way to measure GABA and Glu non-invasively in vivo. GABA detection is particularly challenging and requires special MRS techniques. The most popular is MEscher-GArwood (MEGA) difference editing with single-voxel Point RESolved Spectroscopy (PRESS) localization. This technique has three major limitations: a) MEGA editing is a subtraction technique, hence is very sensitive to scanner instabilities and motion artifacts. b) PRESS is prone to localization errors at high fields (≥. 3. T) that compromise accurate quantification. c) Single-voxel spectroscopy can (similar to a biopsy) only probe steady GABA and Glu levels in a single location at a time.To mitigate these problems, we implemented a 3D MEGA-editing MRS imaging sequence with the following three features: a) Real-time motion correction, dynamic shim updates, and selective reacquisition to eliminate subtraction artifacts due to scanner instabilities and subject motion. b) Localization by Adiabatic SElective Refocusing (LASER) to improve the localization accuracy and signal-to-noise ratio. c) K-space encoding via a weighted stack of spirals provides 3D metabolic mapping with flexible scan times.Simulations, phantom and in vivo experiments prove that our MEGA-LASER sequence enables 3D mapping of GABA. + and Glx (Glutamate. +. Gluatmine), by providing 1.66 times larger signal for the 3.02. ppm multiplet of GABA. + compared to MEGA-PRESS, leading to clinically feasible scan times for 3D brain imaging.Hence, our sequence allows accurate and robust 3D-mapping of brain GABA. + and Glx levels to be performed at clinical 3. T MR scanners for use in neuroscience and clinical applications.
Bibliographical noteFunding Information:
This study was supported by the Austrian Science Fund (FWF), KLI-61 and J3302-B24 to W.B., and by the NIH National Cancer Institute K22 Career Award ( 1K22CA178269-01 ) and KL2 MeRIT Award ( 8KL2TR000168-05 ) of Harvard Clinical and Translational Science Center to O.C.A .
MM acknowledges the support from Biotechnology Research Center (BTRC) grant P41 RR008079 and P41 EB015894 , and NCC P30 NS076408 .
Resources provided to Martinos Center by the Center for Functional Neuroimaging Technologies, P41EB015896, a P41 Regional Resource were supported by the National Institute of Biomedical Imaging and Bioengineering (NIBIB), National Institutes of Health. This work also involved the use of instrumentation supported by the NIH Shared Instrumentation Grant Program and/or High-End Instrumentation Grant Program; specifically, grant S10RR021110.
© 2014 Elsevier Inc.
- Frequency drift correction
- MEGA editing
- Magnetic resonance spectroscopy
- Prospective motion correction
- Real-time correction
- Spiral imaging