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Anatomical Validation of DTI and Tractography 

Anatomical Validation of DTI and Tractography
Chapter:
Anatomical Validation of DTI and Tractography
Author(s):

Nigel I. Lawes C.

and Christopher A. Clark

DOI:
10.1093/med/9780195369779.003.0026
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date: 20 September 2018

Attempts to validate diffusion tensor imaging (DTI) tractography meet two obstacles. Firstly, the factors causing problems are specific to each tract and specific to each species, so transfer of results from other species to humans or from one tract to another cannot be relied upon. Secondly, conventional hodological techniques cannot be used in humans for ethical reasons. In human brains, comparison of blunt dissection of fixed human brains gives comparable results to DTI tractography where tracts are relatively uncomplicated, but both techniques run into similar difficulties where tracts intersect or run closely together. Electrical stimulation to generate electromygraphic responses or disrupt language is a promising mode of validation. In the case of language, electrical disruption produced a division of language pathways similar to DTI tractography and blunt dissection. In contrast, electromyography appeared to identify a larger corticospinal tract than tractography, but this was almost certainly due to inadequate placement of the ROIs used to generate the pathway and to use of a high FA threshold. The somatotopic organization of corticostriatal hand, foot, and mouth pathways is different for functional MRI and DTI tractography, but this is a difficult pathway fraught with problems caused by neighbouring tracts. Various methods of tractography have been compared to known anatomy. Pathways such as cerebello-thalamic tracts, the occipito-frontal fasciculus, geniculate nuclei and somatotopy in the internal capsule have been investigated, generally with positive results. In other species, Gd-DTPA contrast has been used to enhance the signal-to-noise ratio of DTI tractography in fixed primate brains; fibre reconstructions corresponded to known anatomy. Manganese-enhanced T1-weighted images were used to compare the direction of a tract with the principle eigenvector of DTI tractography; the directions were largely parallel except where tracts crossed or terminated. Post-mortem tractography has been compared to in vivo injection of tracers and overlap functions of 0.58–0.98 computed.

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