Two-site reproducibility of cerebellar and brainstem neurochemical profiles with short-echo, single-voxel MRS at 3T

Abstract

Purpose: To determine whether neurochemical concentrations obtained at two MRI sites using clinical 3T scanners can be pooled when a highly optimized, nonvendor short-echo, single-voxel proton MRS pulse sequence is used in conjunction with identical calibration and quantification procedures.

Methods: A modified semi-LASER sequence (TE = 28 ms) was used to acquire spectra from two brain regions (cerebellar vermis and pons) on two Siemens 3T scanners using the same B0 and B1 calibration protocols from two different cohorts of healthy volunteers (N = 24-33 per site) matched for age and body mass index. Spectra were quantified with LCModel using water scaling.

Results: The spectral quality was very consistent between the two sites and allowed reliable quantification of at least 13 metabolites in the vermis and pons compared with 3-5 metabolites in prior multisite magnetic resonance spectroscopy trials using vendor-provided sequences. The neurochemical profiles were nearly identical at the two sites and showed the feasibility to detect interindividual differences in the healthy brain.

Conclusion: Highly reproducible neurochemical profiles can be obtained on different clinical 3T scanners at different sites, provided that the same, optimized acquisition and analysis techniques are used. This will allow pooling of multisite data in clinical studies, which is particularly critical for rare neurological diseases.

Keywords: 3 Tesla; multi-site; reproducibility; spectroscopy.

Figure 1

A) Typical proton spectra obtained from the cerebellar vermis and pons in two different subjects at the two sites using semi-LASER (T_E = 28 ms, T_R = 5 s, 64 averages) at 3 T. The locations of the VOI are shown on the T₁-weighted images. Spectra were processed with a 1 Hz exponential decay and 5 Hz Gaussian functions. Comparable spectral quality and pattern are apparent for each region at both sites. B) LCModel fits of the spectra shown in A without any apodization functions. From top to bottom: the in vivo spectrum, the fit, the residual after subtracting the fit from the in vivo spectrum and the baseline.

Figure 2

Mean metabolite concentrations (in µmol/g) and CRLB (in %) measured in the cerebellar vermis (N = 24 at CMRR, N = 33 at ICM) and pons (N =16 at CMRR, N = 23 at ICM) at the two sites. Error bars represent inter-subject SD. tNAA: total N-acetylaspartate, tCr: total creatine, tCho: total choline, Ins: myo-inositol, Glu: glutamate, Glc: glucose, Tau: taurine, GSH: glutathione, sIns: scyllo-inositol, Asc: ascorbate, Asp: aspartate, GABA: γ-aminobutyric acid, Lac: lactate, Gln: glutamine, NAAG: N-acetylaspartylglutamate.

Figure 3

Relationship between mean CRLB and between-subject coefficients of variance (CV) for all metabolites reported in Figure 2: CV and CRLB ≤ 50% (left) and zoomed CV and CRLB between 0 and 12.5% (right). The solid line represents the identity line.