Posse Stefan, Ramanna Sudhir, Moeller Steen, Vakamudi Kishore, Otazo Ricardo, Sa de La Rocque Guimaraes Bruno, Mullen Michael, Yacoub Essa
Department of Neurology, University of New Mexico, Albuquerque, NM, United States.
Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM, United States.
Front Neurosci. 2025 Mar 12;19:1543206. doi: 10.3389/fnins.2025.1543206. eCollection 2025.
In this study we develop undersampled echo-volumar imaging (EVI) using multi-band/simultaneous multi-slab encoding in conjunction with multi-shot slab-segmentation to accelerate 3D encoding and to reduce the duration of EVI encoding within slabs. This approach combines the sampling efficiency of single-shot 3D encoding with the sensitivity advantage of multi-echo acquisition. We describe the pulse sequence development and characterize the spatial-temporal resolution limits and BOLD sensitivity of this approach for high-speed task-based and resting-state fMRI at 3 T. We study the feasibility of further acceleration using compressed sensing (CS) and assess compatibility with NORDIC denoising.
Multi-band echo volumar imaging (MB-EVI) combines multi-band encoding of up to 6 slabs with CAIPI shifting, accelerated EVI encoding within slabs using up to 4-fold GRAPPA accelerations, 2-shot k-segmentation and partial Fourier acquisitions along the two phase-encoding dimensions. Task-based and resting-state fMRI at 3 Tesla was performed across a range of voxel sizes (between 1 and 3 mm isotropic), repetition times (118-650 ms), and number of slabs (up to 12). MB-EVI was compared with multi-slab EVI (MS-EVI) and multi-band-EPI (MB-EPI).
Image quality and temporal SNR of MB-EVI was comparable to MS-EVI when using 2-3 mm spatial resolution. High sensitivity for mapping task-based activation and resting-state connectivity at short TR was measured. Online deconvolution of T* signal decay markedly reduced spatial blurring and improved image contrast. The high temporal resolution of MB-EVI enabled sensitive mapping of high-frequency resting-state connectivity above 0.3 Hz with 3 mm isotropic voxel size (TR: 163 ms). Detection of task-based activation with 1 mm isotropic voxel size was feasible in scan times as short as 1 min 13 s. Compressed sensing with up to 2.4-fold retrospective undersampling showed negligible loss in image quality and moderate region-specific losses in BOLD sensitivity. NORDIC denoising significantly enhanced fMRI sensitivity without introducing image blurring.
Combining MS-EVI with multi-band encoding enables high overall acceleration factors and provides flexibility for maximizing spatial-temporal resolution and volume coverage. The high BOLD sensitivity of this hybrid MB-EVI approach and its compatibility with online image reconstruction enables high spatial-temporal resolution real-time task-based and resting state fMRI.
在本研究中，我们开发了欠采样回波容积成像（EVI），其使用多频段/同时多层面编码结合多次激发层面分割来加速三维编码，并减少层面内EVI编码的持续时间。这种方法将单次激发三维编码的采样效率与多回波采集的敏感性优势相结合。我们描述了脉冲序列的开发，并表征了这种方法在3T下用于基于任务的高速功能磁共振成像（fMRI）和静息态fMRI时的时空分辨率极限和血氧水平依赖（BOLD）敏感性。我们研究了使用压缩感知（CS）进一步加速的可行性，并评估了与北欧去噪的兼容性。
多频段回波容积成像（MB-EVI）将多达6个层面的多频段编码与可控局部并行采集成像（CAIPI）移位相结合，使用高达4倍的GRAPPA加速、2次激发k空间分割以及沿两个相位编码维度的部分傅里叶采集来加速层面内的EVI编码。在3特斯拉下，针对一系列体素大小（各向同性1至3毫米之间）、重复时间（118 - 650毫秒）和层面数量（多达12个）进行了基于任务的和静息态的fMRI。将MB-EVI与多层EVI（MS-EVI）和多频段回波平面成像（MB-EPI）进行了比较。
当使用2 - 3毫米空间分辨率时，MB-EVI的图像质量和时间信噪比与MS-EVI相当。在短重复时间（TR）下，测量到对基于任务的激活和静息态连接性映射具有高敏感性。T*信号衰减的在线反卷积显著减少了空间模糊并改善了图像对比度。MB-EVI的高时间分辨率能够以3毫米各向同性体素大小（TR：163毫秒）对高于0.3赫兹的高频静息态连接性进行敏感映射。在短至1分13秒的扫描时间内，使用1毫米各向同性体素大小检测基于任务的激活是可行的。高达2.4倍的回顾性欠采样压缩感知在图像质量上显示出可忽略不计的损失，在BOLD敏感性上有适度的区域特异性损失。北欧去噪显著提高了fMRI敏感性，且未引入图像模糊。
将MS-EVI与多频段编码相结合可实现高总体加速因子，并为最大化时空分辨率和容积覆盖提供灵活性。这种混合MB-EVI方法的高BOLD敏感性及其与在线图像重建的兼容性使得基于任务的和静息态的fMRI能够实现高时空分辨率实时成像。
