Keeling Elizabeth G, Bergamino Maurizio, Ragunathan Sudarshan, Quarles C Chad, Newton Allen T, Stokes Ashley M
Barrow Neuroimaging Innovation Center, Barrow Neurological Institute, Phoenix, AZ, United States.
School of Life Sciences, Arizona State University, Tempe, AZ, United States.
Imaging Neurosci (Camb). 2024 Jul 2;2:1-20. doi: 10.1162/imag_a_00217. eCollection 2024 Jul 1.
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 T and T, 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 T-dominant analyses. Using a working memory task, the extent of activation was highest with T -weighting, while smaller clusters were observed with quantitative T and T. 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.
本研究的目的是优化并验证一种使用自旋回波和梯度回波组合采集（SAGE）的多对比、多回波功能磁共振成像（fMRI）方法。研究假设基于SAGE的血氧水平依赖（BOLD）功能磁共振成像（fMRI）将提高灵敏度和空间特异性，同时减少信号丢失。通过12种具有不同加速因子的协议，采集了包含五个回波（2个梯度回波、2个不对称自旋回波和1个自旋回波）的SAGE-fMRI数据，并评估了时间信噪比（tSNR）。然后在15名健康受试者的工作记忆和视觉任务中实施优化后的协议。使用单个回波、定量动态弛豫时间T和T以及动态信号的回波时间相关加权组合进行基于任务的分析。比较这些方法以确定SAGE-fMRI的最佳分析方法。实施2的多频段因子和2.5的灵敏度编码（SENSE）因子可产生足够的时空分辨率，同时将伪影和tSNR损失降至最低。相对于单回波fMRI，SAGE-fMRI观察到更高的BOLD对比噪声比（CNR）和tSNR，特别是在具有大磁化率效应的区域和T主导分析中。在工作记忆任务中，T加权时激活范围最高，而定量T和T时观察到较小的簇。SAGE-fMRI将多梯度回波采集的高BOLD灵敏度与自旋回波采集的改进空间定位相结合，提供两种对比进行分析。SAGE-fMRI具有显著优势，包括提高CNR和tSNR以进行更准确的分析。
