Reconstruction and dissection of the entire human visual pathway using diffusion tensor MRI

Abstract

The human visual system comprises elongated fiber pathways that represent a serious challenge for diffusion tensor imaging (DTI) and fiber tractography: while tracking of frontal fiber bundles may be compromised by the nearby presence of air-filled cavities, nerves, and eye muscles, the anatomic courses of the three main fiber bundles of the optic radiation are subject to pronounced inter-subject variability. Here, tractography of the entire visual pathway was achieved in six healthy subjects at high spatial accuracy, that is, at 1.8 mm isotropic spatial resolution, without susceptibility-induced distortions, and in direct correspondence to anatomic MRI structures. Using a newly developed diffusion-weighted single-shot STEAM MRI sequence, we were able to track the thin optic nerve including the nasal optic nerve fibers, which cross the optic chiasm, and to dissect the optic radiation into the anterior ventral bundle (Meyer's loop), the central bundle, and the dorsal bundle. Apart from scientific applications these results in single subjects promise advances in the planning of neurosurgical procedures to avoid unnecessary damage to the visual fiber system.

Tractography of Meyer's Loop asymmetries

“…Asymmetry measurements in the current study support our hypothesis and demonstrate that the mean ML-TP distance is significantly shorter in the left (39.70 mm) compared to the right (45.64 mm) temporal lobe (table). The asymmetry of the anterior extent of the OR has been initially discussed in dissection studies (Ebeling and Reulen, 1988), and representative figures of the OR in dissection and tractography studies often depict leftward asymmetry (Govindan et al, 2008;Hofer et al, 2010;Mandelstam 2012;Sherbondy et al, 2008). Consistent with the significant leftward asymmetry of ML-TP in our study, Burgel et al (1999) report significant leftward asymmetries of the LGN and OR in a dissection study of ten adult human brains.…”

Challenges of the Anatomy and Diffusion Tensor Tractography of the Meyer Loop

“…In 1 subject, they were unable to reconstruct any bundles of the OR, and this was ascribed to the close vicinity and predominance of the inferior longitudinal fasciculus and the fronto-occipital fasciculus. 29 This result is similar to the inability of Taoka et al 26 to separate the OR from the uncinate fasciculus as discussed above. These studies continue to give an approximation of the pathways, but none can match the criterion standard of the dissection studies (Figs 4 and 5).…”

“…Hofer et al 29 used a new diffusion-weighted sequence with a simple DT-FT algorithm, which is claimed to decrease sus- ceptibility artifacts and geometric distortions and improve spatial resolution. However, their resolution of 1.8 mm is still not adequate to avoid some recognized artifacts, including false-positive tracts.…”

Original article Abnormalities in the normal appearing white matter of the cerebral hemisphere contralateral to a malignant brain tumor detected by diffusion tensor imaging

“…Without the need for a co-registration or alignment technique, which is usually accompanied by a certain degree of blurring, the present work allowed for a direct digital superposition of corresponding data matrices [13]. After preprocessing applying a Neeman correction [25] region-of-interest (ROI) measurements were performed on FA and ADC maps applying the dedicated software package effective Diffusion Coefficient Navigator (DeffCoN, for details see [23]) [3,6,12,13].…”