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Within-session test-retest reproducibility and reliability of auditory cortex GABA+ in individuals with tinnitus using MEGA-sLASER at 3T
Jonathan M. Wai1,2, Kelley Swanberg3, Alex Grassetti2, Martin Gajdošík4, Diana Martinez1,2, and Christoph Juchem5
1Department of Psychiatry, Columbia University Irving Medical Center, New York, NY, United States, 2New York State Psychiatric Institute, New York, NY, United States, 3Department of Experimental Medicine, Lund University, Lund, Sweden, 4Synex Medical, Boston, MA, United States, 5Department of Biomedical Engineering, Columbia University, New York, NY, United States

Synopsis

Keywords: Head & Neck/ENT, Spectroscopy, Precision and accuracy, brain, tinnitus

Motivation: The measurement of GABA+ using in vivo proton magnetic resonance spectroscopy requires adequate reproducibility and reliability for its use in clinical research and as a potential biomarker.

Goal(s): We aimed to determine the within-session test-retest reproducibility and reliability of GABA+ in the auditory cortex of individuals with tinnitus.

Approach: A MEGA-sLASER sequence for GABA+ measurement using two consecutive within-session blocks was performed on 38 participants over 2 scanning days.

Results: GABA+ quantification in the auditory cortex demonstrated similar reproducibility and reliability when using either a total creatine (tCr) or water reference (GABA+/tCr: CV=5.6%, ICC=0.69, 95% CI [0.52-0.80]; GABA+/water: CV=5.6%; ICC=0.73, 95% CI [0.58-0.83]).

Impact: Auditory cortex GABA+ quantification with MEGA-sLASER in a clinical population with GABA+ abnormalities in the region of interest can be achieved with reproducibility and reliability that is comparable to what has been reported in other brain regions of healthy controls.

Introduction

The measurement of GABA using in vivo proton magnetic resonance spectroscopy (1H-MRS) requires adequate reproducibility (determined by the coefficient of variation, CV) and reliability (expressed as the intraclass correlation coefficient, ICC) for its use in clinical research and as a potential biomarker. Previous within-session studies have found acceptable reproducibility with CV<10%1-4 and moderate (ICC=0.5-0.75) to good (ICC=0.75-0.9) reliability1,3,5 but have often focused on healthy participants. The replication of this research in a clinical population, where there may be pathological findings, is important for the dissemination of 1H-MRS in clinical use. In this secondary analysis, we used a MEGA-sLASER sequence6 for the measurement of GABA+ (GABA with macromolecules) in participants with tinnitus, a condition where metabolite irregularities in the auditory cortex have been reported7,8.

Methods

Scans were performed using a Siemens 3T MAGNETOM Prisma scanner with the vendor’s 32-channel head receive coil (Siemens Healthineers, Erlangen, Germany) on 38 participants (21/17 m/f, age 42±12years) enrolled in a clinical trial for the treatment of tinnitus (Clinicaltrials.gov ID NCT03336398). Two baseline GABA+ acquisitions (blocks 1 and 2, 6.4min each) beginning approximately 15min into the scanning session were performed on each of two scan days (Fig. 1).

Data were acquired from a 25x40x20-mm3 voxel (Fig. 2A) aligned with the Sylvian fissure in the transverse plane and adjusted to capture the entirety of the primary auditory cortex. GABA+ was measured with sLASER acquisitions J-difference-edited (JDE) for GABA+ detection (TE=72ms, TR=2s, NR=192 per block). Sequence crushers (maximum 24mT/m, duration 1.3ms) and 16-step cogwheel phase cycling schemes9 were optimized by DOTCOPS10,11; water suppression was achieved by 7-pulse VAPOR12.

Metabolite spectra were processed in INSPECTOR13 with individual traces eddy-current corrected, and phase- and frequency-aligned. Corresponding averaged edit-on and edit-off spectra were aligned and subtracted to yield averaged difference spectra with isolated GABA+ and co-edited Glx with NAA. GABA+ JDE difference spectra and corresponding edit-off spectra were quantified in LCModel (v. 6.3, S. Provencher)14 (Fig. 2B-2D). Basis sets were density-matrix simulated at 2048 complex points in MARSS15 using published chemical shifts and J-coupling constants16 with realistic pulse shapes defined over a 1283-point cubic spatial grid.

Concentrations were referenced to an assumed 10mM total creatine (tCr) per voxel as well as internal water. For this within-subject analysis, water molarity was estimated at 42800mM per voxel according to published occipital cortex tissue water fractions in healthy adults17,18, with assumed tissue partial volumes at 40% grey matter, 40% white matter, and 20% cerebral spinal fluid. T2 for GABA, creatine, and water were set to 75, 144, and 107ms, respectively19,20.

CV, ICC, and Pearson’s r values were calculated in SPSS v.29.0. Data were inspected for outliers and skewness using Bland-Altman plots.

Results

Scan parameters according to minimum reporting standards guidelines21 are shown in Fig. 3. JDE GABA+ edit-off spectra (76 averaged spectra each for blocks 1 and 2) had no difference in SNR (t(75)=-0.604, p=0.547) or FWHM (t(75)=-0.083, p=0.93) of the 2.01-ppm NAA singlet. No data sets acquired were discarded due to visually poor spectral quality or quantifiability. GABA Cramér-Rao Lower Bounds were <20% (mean=11.0±1.5, range 8-17).

Auditory cortex GABA+ quantification demonstrated similar reproducibility and reliability when referenced to either tCr or water (GABA+/tCr: CV=5.6%, ICC=0.69, 95% CI [0.52-0.80]; GABA+/water: CV=5.6%; ICC=0.73, 95% CI [0.58-0.83]) (Fig. 4). The data were normally distributed and there was a moderate correlation between block 1 and block 2 (GABA/tCr: r=0.531, GABA/water: r=0.576). Bland-Altman plots for both creatine and water referenced measures showed >95% (two outliers each) of blocks falling within repeatability coefficients and no skewness (Fig. 5).

Discussion

Auditory cortex GABA+ quantification with MEGA-sLASER in a clinical population with reported GABA+ abnormalities in the region of interest can be achieved with reproducibility and reliability that is comparable to other brain regions of healthy controls. GABA/water demonstrated better ICC when compared to GABA/Cr, though both fell within the “moderate” range, with the ICC for GABA/water approaching “good”5 for average measures. The 6.4min acquisition time for the MEGA-sLASER sequence was feasible for clinical use.

Conclusions

MEGA-sLASER for GABA+ quantification in the auditory cortex has appropriate reproducibility and reliability for use as an averaged measure in research with a clinical population with described GABA+ abnormalities.

Acknowledgements

This work was supported by NIAAA grant K23AA028295 (JMW) and USAMRAA grant W81XWH-18-1-0221 (DM). We would also like to acknowledge Kay Igwe for her assistance with data management.

References

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Figures

Figure 1. Outline of the experimental study. A secondary analysis was performed on of a subset of a participants (n=38) enrolled in trial for the treatment of tinnitus. Reproducibility and reliability were compared between blocks 1 and 2 over both scan days (76 scans total, 2 blocks each scan). The large variation in the time between scans was due to a COVID-19 research pause. MP-RAGE: magnetization-prepared 180 degrees radio-frequency pulses and rapid gradient-echo, JDE: J-difference editing, MEGA-sLASER: Mescher-Garwood semi localization by adiabatic selective refocusing.

Figure 2. Voxel placement for GABA+ quantification. A) Placement of the voxel over the auditory cortex. B-D) Sample data set for the isolation of GABA showing the B) J-difference editing subtraction, C) GABA fitting from the difference spectrum, and D) tCr fitting from the edit-off spectrum. ppm: parts per million, LCM: linear combination modeling. Metabolites of interest: Cr: creatine, pCr: phosphocreatine, tCr: total creatine, Glx: glutamate and glutamine, Glu: glutamate, Gln: glutamine, NAA: N-acetylaspartate

Figure 3. Summary of scanning details according to guidelines for the minimum reporting standards of magnetic resonance spectroscopy studies.

Figure 4. Means of quality assurance measures and descriptive statistics for each scan followed by the reproducibility and reliability measures for GABA/tCr and GABA/water. FWHM: full-width half maximum, SNR: signal to noise ratio, NAA: N-acetylaspartate, tCr: total creatine, CV: coefficient of variation, ICC: intraclass correlation coefficient, *: p < 0.001 (2-tailed).

Figure 5. Bland-Altman plots showing >95% of points within the limits of agreement and no skewness. The interscan mean of GABA+ is displayed on the x-axis and difference between these two measurements on the y-axis. The solid red line displays the mean of all scans 1 and 2, and the dotted black line represents the limits of agreement. tCr: total creatine. GABA+: GABA with macromolecule contamination.

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)
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DOI: https://doi.org/10.58530/2024/1944