Validation of High-Resolution Tractography Against In Vivo Tracing in the Macaque Visual Cortex.

Hojjatollah Azadbakht,Mark Augath,Hamied A Haroon,Alex De Crespigny,Geoffrey J M Parker,Helen E D'Arceuil,Laura M Parkes,Nikos K Logothetis

doi:10.1093/cercor/bhu326

Abstract

Diffusion magnetic resonance imaging (MRI) allows for the noninvasive in vivo examination of anatomical connections in the human brain, which has an important role in understanding brain function. Validation of this technique is vital, but has proved difficult due to the lack of an adequate gold standard. In this work, the macaque visual system was used as a model as an extensive body of literature of in vivo and postmortem tracer studies has established a detailed understanding of the underlying connections. We performed probabilistic tractography on high angular resolution diffusion imaging data of 2 ex vivo, in vitro macaque brains. Comparisons were made between identified connections at different thresholds of probabilistic connection “strength,” and with various tracking optimization strategies previously proposed in the literature, and known connections from the detailed visual system wiring map described by Felleman and Van Essen (1991; FVE91). On average, 74% of connections that were identified by FVE91 were reproduced by performing the most successfully optimized probabilistic diffusion MRI tractography. Further comparison with the results of a more recent tracer study ( Markov et al. 2012) suggests that the fidelity of tractography in estimating the presence or absence of interareal connections may be greater than this.

Highlights

Magnetic resonance diffusion images allow in vivo estimation of cerebral anatomical connectivity patterns using techniques such as tractography
Average accuracies of 77% and 70% of connections at the optimum thresholds were found in Dataset 1 (D1) and Dataset 2 (D2), respectively (Table 1), showing good agreement between the results from each brain, despite quite different acquisition parameters
These “false” connections were compared with the results of a more recent quantitative tracer study (Markov et al 2012) that has identified a number of additional pathways, as indicated by the footnotes “a and b” in Tables 2 and 3

Summary

Introduction

Magnetic resonance diffusion images allow in vivo estimation of cerebral anatomical connectivity patterns using techniques such as tractography. One approach to validation is to use computer-generated software phantoms (Gossl et al 2002; Tournier et al 2002; Lazar and Alexander 2003; Alexander 2005; Leemans et al 2005; Watanabe et al 2006; Descoteaux et al 2007; Iturria-Medina et al 2007; Sakaie and Lowe 2007) or physical phantoms (Basser et al 1994; van Doorn et al 1996; Van Donkelaar et al 1999; von dem Hagen and Henkelman 2002; Lin et al 2003; Fieremans et al 2005; Perrin et al 2005; Yanasak and Allison 2006; Hubbard et al 2015) These phantoms are relatively easy to define and manipulate by the user, but may grossly over-approximate the in vivo situation that is being simulated, as the complexities of white matter structures are difficult to reproduce. Comparisons with such studies have highlighted the various attributes and pitfalls of different classes of fiber tracking methodologies

Objectives

Methods

Results

Discussion

Conclusion