Integrated Short-TE and Hadamard-edited Multi-Sequence (ISTHMUS) for Advanced MRS

To examine data quality and reproducibility using ISTHMUS, which has been implemented as the standardized MR spectroscopy sequence for the multi-site Healthy Brain and Child Development (HBCD) study.

ISTHMUS is the consecutive acquisition of short-TE PRESS (32 transients) and long-TE HERCULES (224 transients) data with dual-TE water reference scans. Voxels were positioned in the centrum semiovale, dorsal anterior cingulate cortex, posterior cingulate cortex and bilateral thalamus regions. After acquisition, ISTHMUS data were separated into the PRESS and HERCULES portions for analysis and modeled separately using Osprey. In vivo experiments were performed in 10 healthy volunteers (6 female; 29.5±6.6 years). Each volunteer underwent two scans on the same day. Differences in metabolite measurements were examined. T₂ correction based on the dual-TE water integrals were compared with: 1) T₂ correction based the default white matter and gray matter T₂ reference values in Osprey; 2) shorter WM and GM T₂ values from recent literature; and 3) reduced CSF fractions.

No significant difference in linewidth was observed between PRESS and HERCULES. Bilateral thalamus spectra had produced significantly higher (p<0.001) linewidth compared to the other three regions. Linewidth measurements were similar between scans, with scan-to-scan differences under 1 Hz for most subjects. Paired t-tests indicated a significant difference only in PRESS NAAG between the two thalamus scans (p=0.002). T₂ correction based on shorter T₂ values showed better agreement to the dual-TE water integral ratio.

ISTHMUS facilitated and standardized acquisition and post-processing and reduced operator workload to eliminate potential human error.