Test-Retest Reproducibility of Reduced-Field-of-View Density-Weighted CRT MRSI at 3T

Abstract

Quantifying an imaging modality's ability to reproduce results is important for establishing its utility. In magnetic resonance spectroscopic imaging (MRSI), new acquisition protocols are regularly introduced which improve upon their precursors with respect to signal-to-noise ratio (SNR), total acquisition duration, and nominal voxel resolution. This study has quantified the within-subject and between-subject reproducibility of one such new protocol (reduced-field-of-view density-weighted concentric ring trajectory (rFOV-DW-CRT) MRSI) by calculating the coefficient of variance of data acquired from a test-retest experiment. The posterior cingulate cortex (PCC) and the right superior corona radiata (SCR) were selected as the regions of interest (ROIs) for grey matter (GM) and white matter (WM), respectively. CVs for between-subject and within-subject were consistently around or below 15% for Glx, tCho, and Myo-Ins, and below 5% for tNAA and tCr.

Keywords: imaging; magnetic; non-Cartesian; nuclear; reproducibility; resonance; spectroscopy; test–retest.

Figure 1

Quantification results from LCModel are plotted as five metabolite maps for each of the four subjects shown in both their native-patient space and transformed into MNI-152. All color maps are relative intensity with respect to each subject and metabolite. The # symbol refers to the word “number”.

Figure 2

Two scans for each subject were acquired and then converted into MNI-152 space to facilitate direct comparison between voxels. The first and second scans are represented in blue and semi-transparent red, respectively. The # symbol refers to the word “number”.

Figure 3

Transverse profiles of the standard MNI-152-2mm-Brain with the PCC and SCR ROIs defined by the Harvard–Oxford Cortical Atlas (GM) and the JHU ICBM-DTI-81 White-Matter Labels Atlas (WM). Voxels where the ROI and the subject’s scan overlap are highlighted in red and included within the statistical analysis. There is also a third arbitrary (ARB) ROI selected to demonstrate the generalizability of the technique. The # symbol refers to the word “number”.

Figure 4

Example spectral reconstructions (red) produced by LCModel using the specifics detailed in the methods sections, overlayed with the pre-processed spectrum (black). Data come from the first scan of Subject 1 and are presented as a 3 × 3 sample window for 9 spectra roughly centered in the localization volume. The locations of the spectra presented above are found within the yellow box overlayed in the anatomical image above.

Figure 5

All three viewing angles for the VOI alignment of both scans for Subject 2. The misalignment between the two is visible along the sagittal and coronal planes. This misalignment was the greatest contributor to the small cross-coverage in the corresponding MNI-152 space, as seen in Figure 2. The test and retest scans for subject 2 are represented by the colors red and blue respectively.