Normalizing data from GABA-edited MEGA-PRESS implementations at 3 Tesla

Abstract

Standardization of results is an important milestone in the maturation of any truly quantitative methodology. For instance, a lack of measurement agreement across imaging platforms limits multisite studies, between-study comparisons based on the literature, and inferences based on and the generalizability of results. In GABA-edited MEGA-PRESS, two key sources of differences between implementations are: differences in editing efficiency of GABA and the degree of co-editing of macromolecules (MM). In this work, GABA editing efficiency κ and MM-co-editing μ constants are determined for three widely used MEGA-PRESS implementations (on the most common MRI platforms; GE, Philips, and Siemens) by phantom experiments. Implementation-specific κ,μ-corrections were then applied to two in vivo datasets, one consisted of 8 subject scanned on the three platforms and the other one subject scanned eight times on each platform. Manufacturer-specific κ and μ values were determined as: κGE = 0.436, κSiemens = 0.366 and κPhilips = 0.394 and μGE = 0.83, μSiemens = 0.625 and μPhilips = 0.75. Applying the κ,μ-correction on the Cr-referenced data decreased the coefficient of variation (CV) of the data for both in vivo data sets (multisubjects: uncorrected CV = 13%, κ,μ-corrected CV = 5%, single subject: uncorrected CV = 23%, κ,μ-corrected CV = 13%) but had no significant effect on mean GABA levels. For the water-referenced results, CV increased in the multisubject data (uncorrected CV = 6.7%, κ,μ-corrected CV = 14%) while it decreased in the single subject data (uncorrected CV = 24%, κ,μ-corrected CV = 21%) and manufacturer was a significant source of variance in the κ,μ-corrected data. Applying a correction for editing efficiency and macromolecule contamination decreases the variance between different manufacturers for creatine-referenced data, but other sources of variance remain.

Gamma-Aminobutyric Acid Levels in the Anterior Cingulate Cortex of Perimenopausal Women With Depression: A Magnetic Resonance Spectroscopy Study

“…Unsuppressed water was used for water scaling and correction of frequency and phase. The spectra were fitted using TARQUIN software (Wilson et al, 2011; Mullins et al, 2014; Harris et al, 2017). GABA peaks were quantified calculated using the water-scaled method, as described previously (Wilson et al, 2011; Mullins et al, 2014; Harris et al, 2017).…”

Contribution of macromolecules to brain 1H MR spectra: Experts' consensus recommendations

“…92 The relative contributions of GABA and MM to the edited GABA+ resonance also depend on the timing pattern of the editing pulse. 107 Improving the selectivity of the editing pulse by performing single quantum editing with a numerically optimized pulse has been used to reduce MM coediting. 108 Additional strategies could be employed using multiple quantum filtering to reduce MM coediting by adjusting the frequency separation between the two frequency selection bands and by repeating the double-band selective pulse.…”

“…Conversely, a higher bandwidth will reduce the susceptibility to misadjustment of the editing pulse frequency caused by motion and field drift, 106 which alters MM coediting 92 . The relative contributions of GABA and MM to the edited GABA+ resonance also depend on the timing pattern of the editing pulse 107 …”

Multi-vendor standardized sequence for edited magnetic resonance spectroscopy

“…A large multi-site study involving diverse implementations of MEGA-PRESS across sites and vendors revealed relatively good agreement (albeit with statistically significant differences) between sites and vendors. This study suggested that approximately 30% of the total variance in the GABA þ data was attributed to site-and vendor-level differences in the implementation of MEGA-PRESS (Mikkelsen. et al, 2017).…”