Division of MRI Research, Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Division of MRI Research, Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Neuroimage. 2020 Dec;223:117371. doi: 10.1016/j.neuroimage.2020.117371. Epub 2020 Sep 12.
Arterial Spin Labeling (ASL) MRI can provide quantitative images that are sensitive to both time averaged blood flow and its temporal fluctuations. 3D image acquisitions for ASL are desirable because they are more readily compatible with background suppression to reduce noise, can reduce signal loss and distortion, and provide uniform flow sensitivity across the brain. However, single-shot 3D acquisition for maximal temporal resolution typically involves degradation of image quality through blurring or noise amplification by parallel imaging. Here, we report a new approach to accelerate a common stack of spirals 3D image acquisition by pseudo golden-angle rotation and compressed sensing reconstruction without any degradation of time averaged blood flow images.
28 healthy volunteers were imaged at 3T with background-suppressed unbalanced pseudo-continuous ASL combined with a pseudo golden-angle Stack-of-Spirals 3D RARE readout. A fully-sampled perfusion-weighted volume was reconstructed by 3D non-uniform Fast Fourier Transform (nuFFT) followed by sum-of-squares combination of the 32 individual channels. Coil sensitivities were estimated followed by reconstruction of the 39 single-shot volumes using an L-wavelet Compressed-Sensing reconstruction. Finally, brain connectivity analyses were performed in regions where BOLD signal suffers from low signal-to-noise ratio and susceptibility artifacts.
Image quality, assessed with a non-reference 3D blurring metric, of full time averaged blood flow was comparable to a conventional interleaved acquisition. The temporal resolution provided by the acceleration enabled identification and quantification of resting-state networks even in inferior regions such as the amygdala and inferior frontal lobes, where susceptibility artifacts can degrade conventional resting-state fMRI acquisitions.
This approach can provide measures of blood flow modulations and resting-state networks for free within any research or clinical protocol employing ASL for resting blood flow.
动脉自旋标记（ASL）MRI 可以提供对时间平均血流及其时间波动都敏感的定量图像。由于更易于与背景抑制结合以降低噪声，减少信号损失和失真，并在整个大脑中提供均匀的流动敏感性，因此 3D 图像采集对于 ASL 是理想的。然而，为了获得最大的时间分辨率，单次 3D 采集通常会通过并行成像导致图像质量下降，出现模糊或噪声放大。在这里，我们报告了一种新的方法，通过伪黄金角旋转和压缩感知重建来加速常见的螺旋 3D 图像采集，而不会对时间平均血流图像造成任何退化。
28 名健康志愿者在 3T 上进行了成像，采用背景抑制的非平衡伪连续 ASL 结合伪黄金角 Stack-of-Spirals 3D RARE 读出。通过 3D 非均匀快速傅里叶变换（nuFFT）重建全灌注加权体积，然后通过 32 个单独通道的和的平方组合。在使用 L 波压缩感知重建对 39 个单次采集体积进行重建之前，估计了线圈灵敏度。最后，在 BOLD 信号受到低信噪比和磁化率伪影影响的区域进行了脑连接分析。
使用非参考 3D 模糊度度量评估的全时平均血流的图像质量与常规的交错采集相当。加速提供的时间分辨率能够识别和量化静息状态网络，即使在易受磁化率伪影影响的区域，如杏仁核和下额叶。
这种方法可以在任何采用 ASL 进行静息血流的研究或临床协议中，免费提供血流调制和静息状态网络的测量。
