Optimization and Validation of Multi-Echo, Multi-Contrast Sage Acquisition in fMRI

Authors

Elizabeth G Keeling
Maurizio Bergamino
Sudarshan Ragunathan
C Chad Quarles
Allen T Newton
Ashley M Stokes

Language

English

Publication Date

7-1-2024

Journal

Imaging Neuroscience

DOI

10.1162/imag_a_00217

PMID

39449748

PMCID

PMC11497078

PubMedCentral® Posted Date

7-2-2024

PubMedCentral® Full Text Version

Post-print

Abstract

The purpose of this study was to optimize and validate a multi-contrast, multi-echo fMRI method using a combined spin- and gradient-echo (SAGE) acquisition. It was hypothesized that SAGE-based blood oxygen level-dependent (BOLD) functional MRI (fMRI) will improve sensitivity and spatial specificity while reducing signal dropout. SAGE-fMRI data were acquired with five echoes (2 gradient-echoes, 2 asymmetric spin-echoes, and 1 spin-echo) across 12 protocols with varying acceleration factors, and temporal SNR (tSNR) was assessed. The optimized protocol was then implemented in working memory and vision tasks in 15 healthy subjects. Task-based analysis was performed using individual echoes, quantitative dynamic relaxation times T2*and T2, and echo time-dependent weighted combinations of dynamic signals. These methods were compared to determine the optimal analysis method for SAGE-fMRI. Implementation of a multiband factor of 2 and sensitivity encoding (SENSE) factor of 2.5 yielded adequate spatiotemporal resolution while minimizing artifacts and loss in tSNR. Higher BOLD contrast-to-noise ratio (CNR) and tSNR were observed for SAGE-fMRI relative to single-echo fMRI, especially in regions with large susceptibility effects and for T2-dominant analyses. Using a working memory task, the extent of activation was highest with T2*-weighting, while smaller clusters were observed with quantitative T2*and T2. SAGE-fMRI couples the high BOLD sensitivity from multi-gradient-echo acquisitions with improved spatial localization from spin-echo acquisitions, providing two contrasts for analysis. SAGE-fMRI provides substantial advantages, including improving CNR and tSNR for more accurate analysis.

Keywords

functional MRI (fMRI), multi-echo fMRI, spin-echo fMRI, BOLD contrast, BOLD contrast-to-noise ratio (CNR)

Published Open-Access

yes

Recommended Citation

Keeling, Elizabeth G; Bergamino, Maurizio; Ragunathan, Sudarshan; et al., "Optimization and Validation of Multi-Echo, Multi-Contrast Sage Acquisition in fMRI" (2024). Faculty, Staff and Student Publications. 6451.
https://digitalcommons.library.tmc.edu/uthgsbs_docs/6451