Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
Q bio Inc., San Carlos, CA, USA.
Neuroimage. 2021 Nov;243:118530. doi: 10.1016/j.neuroimage.2021.118530. Epub 2021 Aug 28.
The first phase of the Human Connectome Project pioneered advances in MRI technology for mapping the macroscopic structural connections of the living human brain through the engineering of a whole-body human MRI scanner equipped with maximum gradient strength of 300 mT/m, the highest ever achieved for human imaging. While this instrument has made important contributions to the understanding of macroscale connectional topology, it has also demonstrated the potential of dedicated high-gradient performance scanners to provide unparalleled in vivo assessment of neural tissue microstructure. Building on the initial groundwork laid by the original Connectome scanner, we have now embarked on an international, multi-site effort to build the next-generation human 3T Connectome scanner (Connectome 2.0) optimized for the study of neural tissue microstructure and connectional anatomy across multiple length scales. In order to maximize the resolution of this in vivo microscope for studies of the living human brain, we will push the diffusion resolution limit to unprecedented levels by (1) nearly doubling the current maximum gradient strength from 300 mT/m to 500 mT/m and tripling the maximum slew rate from 200 T/m/s to 600 T/m/s through the design of a one-of-a-kind head gradient coil optimized to minimize peripheral nerve stimulation; (2) developing high-sensitivity multi-channel radiofrequency receive coils for in vivo and ex vivo human brain imaging; (3) incorporating dynamic field monitoring to minimize image distortions and artifacts; (4) developing new pulse sequences to integrate the strongest diffusion encoding and highest spatial resolution ever achieved in the living human brain; and (5) calibrating the measurements obtained from this next-generation instrument through systematic validation of diffusion microstructural metrics in high-fidelity phantoms and ex vivo brain tissue at progressively finer scales with accompanying diffusion simulations in histology-based micro-geometries. We envision creating the ultimate diffusion MRI instrument capable of capturing the complex multi-scale organization of the living human brain - from the microscopic scale needed to probe cellular geometry, heterogeneity and plasticity, to the mesoscopic scale for quantifying the distinctions in cortical structure and connectivity that define cyto- and myeloarchitectonic boundaries, to improvements in estimates of macroscopic connectivity.
人类连接组计划的第一阶段开创了磁共振成像技术的进步，通过工程设计一种全身人体磁共振成像扫描仪，该扫描仪配备了 300 mT/m 的最大梯度强度，这是人类成像中从未达到的最高强度，从而绘制活体人脑的宏观结构连接图。虽然该仪器对理解宏观连接拓扑结构做出了重要贡献，但它也展示了专用高梯度性能扫描仪提供无与伦比的神经组织微观结构体内评估的潜力。在原始连接体扫描仪奠定的初步基础上，我们现在已经开始进行一项国际、多站点的努力，以构建下一代人类 3T 连接体扫描仪（连接体 2.0），该扫描仪针对多个尺度的神经组织微观结构和连接解剖结构进行优化。为了使这种活体显微镜对活体人脑研究的分辨率最大化，我们将通过以下方式将扩散分辨率极限推向前所未有的水平：(1) 通过设计一种独特的头部梯度线圈，将当前最大梯度强度从 300 mT/m 提高到 500 mT/m，将最大上升速率从 200 T/m/s 提高到 600 T/m/s，从而最大限度地减少外周神经刺激；(2) 开发用于活体和离体人脑成像的高灵敏度多通道射频接收线圈；(3) 结合动态场监测，最大限度地减少图像失真和伪影；(4) 开发新的脉冲序列，将活体人脑有史以来最强的扩散编码和最高的空间分辨率集成在一起；(5) 通过在逐步更精细的尺度上用基于组织学的微观几何结构进行扩散模拟，在高保真度体模和离体脑组织中对扩散微观结构指标进行系统验证，对下一代仪器获得的测量值进行校准。我们设想创建一种终极扩散磁共振成像仪器，能够捕捉活体人脑的复杂多尺度组织——从探测细胞几何形状、异质性和可塑性所需的微观尺度，到量化皮质结构和连接性区别所需的介观尺度，以改善宏观连接的估计。
