Tuch David S, Wisco Jonathan J, Khachaturian Mark H, Ekstrom Leeland B, Kötter Rolf, Vanduffel Wim
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, 149 13th Street, Charlestown, MA 02129, USA.
Philos Trans R Soc Lond B Biol Sci. 2005 May 29;360(1457):869-79. doi: 10.1098/rstb.2005.1651.
Diffusion-weighted magnetic resonance imaging holds substantial promise as a technique for non-invasive imaging of white matter (WM) axonal projections. For diffusion imaging to be capable of providing new insight into the connectional neuroanatomy of the human brain, it will be necessary to histologically validate the technique against established tracer methods such as horseradish peroxidase and biocytin histochemistry. The macaque monkey provides an ideal model for histological validation of the diffusion imaging method due to the phylogenetic proximity between humans and macaques, the gyrencephalic structure of the macaque cortex, the large body of knowledge on the neuroanatomic connectivity of the macaque brain and the ability to use comparable magnetic resonance acquisition protocols in both species. Recently, it has been shown that high angular resolution diffusion imaging (HARDI) can resolve multiple axon orientations within an individual imaging voxel in human WM. This capability promises to boost the accuracy of tract reconstructions from diffusion imaging. If the macaque is to serve as a model for histological validation of the diffusion tractography method, it will be necessary to show that HARDI can also resolve intravoxel architecture in macaque WM. The present study therefore sought to test whether the technique can resolve intravoxel structure in macaque WM. Using a HARDI method called q-ball imaging (QBI) it was possible to resolve composite intravoxel architecture in a number of anatomic regions. QBI resolved intravoxel structure in, for example, the dorsolateral convexity, the pontine decussation, the pulvinar and temporal subcortical WM. The paper concludes by reviewing remaining challenges for the diffusion tractography project.
扩散加权磁共振成像作为一种用于白质（WM）轴突投射的非侵入性成像技术，具有巨大的前景。为了使扩散成像能够为人类大脑的连接神经解剖学提供新的见解，有必要通过组织学方法，对照既定的示踪剂方法（如辣根过氧化物酶和生物素组织化学）来验证该技术。猕猴由于与人类在系统发育上接近、猕猴皮层的脑回结构、关于猕猴大脑神经解剖连接的大量知识以及在两个物种中使用可比磁共振采集协议的能力，为扩散成像方法的组织学验证提供了理想模型。最近，研究表明高角分辨率扩散成像（HARDI）可以分辨人类白质中单个成像体素内的多个轴突方向。这种能力有望提高扩散成像中纤维束重建的准确性。如果猕猴要作为扩散纤维束成像方法组织学验证的模型，就有必要证明HARDI也能分辨猕猴白质中的体素内结构。因此，本研究旨在测试该技术是否能分辨猕猴白质中的体素内结构。使用一种称为q球成像（QBI）的HARDI方法，能够在多个解剖区域分辨复合体素内结构。例如，QBI在背外侧凸面、脑桥交叉、丘脑枕和颞叶皮质下白质中分辨出了体素内结构。本文最后回顾了扩散纤维束成像项目仍然面临的挑战。
