A comparison of spectral quality in magnetic resonance spectroscopy data acquired with and without a novel EPI-navigated PRESS sequence in school-aged children with fetal alcohol spectrum disorders

Abstract

Single voxel spectroscopy (SVS) can generate useful information regarding metabolite concentrations provided that the MR signal can be averaged over several minutes during which the subject remains stationary. This requirement can be particularly challenging for children who cannot otherwise be scanned without sedation. To address this problem we developed an EPI volume navigated (vNav) SVS PRESS sequence, which applies real-time head pose (location and orientation), frequency, and first-order B0 shim adjustments. A water-independent preprocessing algorithm removes residual frequency and phase shifts resulting from within-TR movements. We compare results and performance of the standard and vNav PRESS sequences in a sample of 9- to 10-year-olds from a South African cohort of children with fetal alcohol spectrum disorders (FASD) and healthy controls. Magnetic resonance spectroscopy (MRS) data in the deep cerebellar nuclei were initially acquired with the standard PRESS sequence. The children were re-scanned 1 year later with the vNav PRESS sequence. Good quality data were acquired in 73% using the vNav PRESS sequence, compared to only 50% for the standard PRESS sequence. Additionally, tighter linewidths and smaller variances in the measured concentrations were observed. These findings confirm previous reports demonstrating the efficacy of our innovative vNav sequence with healthy volunteers and young children with HIV and expand its application to a school-aged population with FASD-disorders often associated with attention problems and hyperactivity. This study provides the most direct evidence to date regarding degree to which these new methods can improve data quality in research studies employing MRS.

Fig. 1

A) SVS volume of interest in the cerebellar deep nuclei, shown overlaid on the corresponding localising T2 turbo spin echo images B) Navigator FOV placement for scans with VOI in the cerebellum, it is angulated to ensure coverage of the cerebellum without increasing navigator duration

Fig. 2

Pie charts showing the proportion of data excluded from each of the data sets due to either bad quality spectra or technical failures of the navigator

Fig. 3

Navigator: magnitude image of first echo (used for PACE motion estimation) (left) and unwrapped field map (right)

Fig. 4

Box-and-whisker plots showing of the maximum absolute vector translations and rotations of the child’s head from the start of the scan, expressed firstly about the centre of the navigator volume, representing gross head rotation and translation, and secondly about the centre of the SVS voxel, translations only.

Fig. 5

Box-and-whisker plots of linewidth and signal-to-noise ratio (S/N), as measured by LCModel, for all scans without the vNAV (2009) and all scans with the vNAV (2010)

Fig. 6

Box-and-whisker plots comparing the variance and range of metabolite concentrations in control children using the PRESS (2009) and vNav PRESS (2010) sequences. Data points were excluded if their %SD exceeded 30% with the resultant number of data points given by N.