شارك في تحليل بنية الدماغ والدالة باستخدام الرنين المغناطيسي الوظيفي وانتشارها المرجحة التصوير

Summary

We describe a novel approach for simultaneous analysis of brain function and structure using magnetic resonance imaging (MRI). We assess brain structure with high-resolution diffusion-weighted imaging and white-matter fiber tractography. Unlike standard structural MRI, these techniques allow us to directly relate anatomical connectivity to functional properties of brain networks.

Abstract

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when studying the brain, as the functional role that a brain area fulfills may be largely defined by its connections to other brain areas. In this report, we describe a novel, non-invasive approach for relating brain structure and function using magnetic resonance imaging (MRI). This approach, a combination of structural imaging of long-range fiber connections and functional imaging data, is illustrated in two distinct cognitive domains, visual attention and face perception. Structural imaging is performed with diffusion-weighted imaging (DWI) and fiber tractography, which track the diffusion of water molecules along white-matter fiber tracts in the brain (Figure 1). By visualizing these fiber tracts, we are able to investigate the long-range connective architecture of the brain. The results compare favorably with one of the most widely-used techniques in DWI, diffusion tensor imaging (DTI). DTI is unable to resolve complex configurations of fiber tracts, limiting its utility for constructing detailed, anatomically-informed models of brain function. In contrast, our analyses reproduce known neuroanatomy with precision and accuracy. This advantage is partly due to data acquisition procedures: while many DTI protocols measure diffusion in a small number of directions (e.g., 6 or 12), we employ a diffusion spectrum imaging (DSI)^{1, 2} protocol which assesses diffusion in 257 directions and at a range of magnetic gradient strengths. Moreover, DSI data allow us to use more sophisticated methods for reconstructing acquired data. In two experiments (visual attention and face perception), tractography reveals that co-active areas of the human brain are anatomically connected, supporting extant hypotheses that they form functional networks. DWI allows us to create a “circuit diagram” and reproduce it on an individual-subject basis, for the purpose of monitoring task-relevant brain activity in networks of interest.

Protocol

1. Equipment for MR Data Acquisition Figures 2 and 3 summarize a number of choices to be made in diffusion MRI acquisition, data reconstruction, and fiber tracking. Keep in mind that these choices typically involve trade-offs, and the best choice may depend upon one’s research objectives. For example, DSI and multi-shell HARDI (see Figure 2) typically use higher “b-values” (i.e., stronger diffusion weighting) than DTI. As a result, these methods have be…

Discussion

High-resolution DWI and fiber tractography provide a powerful approach for examining the connective structure of the human brain. Here, we present evidence that this structural architecture is meaningfully related to brain function, assessed by fMRI. By using tractography seeds based on fMRI task activation, we find evidence that brain areas which are co-active during visual attention are anatomically connectedconsistent with prior knowledge of functional neuroanatomy (Figure 7). Similarly, the functiona…