Diffusion anisotropy and diffusivity of white matter tracts within the temporal stem in Alzheimer disease: evaluation of the "tract of interest" by diffusion tensor tractography

Abstract

Purpose: Our aim was to determine whether diffusion anisotropy and diffusivity of white matter tracts of the temporal stem in patients with Alzheimer (AD) can be evaluated independently by using diffusion tensor tractography.

Materials and methods: Subjects included 15 patients with AD (11 women and 4 men; mean age, 74 years) and 15 age-matched control subjects (11 women and 4 men; mean age, 72 years). Diffusion tensor images were acquired by using echo-planar imaging. We drew tractographies of the uncinate fasciculus, inferior occipitofrontal fasciculus, and Meyer's loop, with diffusion tensor analysis software. We measured diffusion anisotropy, diffusivity, and the number of voxels along the "tracts of interest" and used the Student t test to compare results between patients with AD and controls.

Results: Values of diffusion anisotropy of the bilateral uncinate fasciculus and left inferior occipitofrontal fasciculus were significantly lower for patients with AD than for controls. Also, values of diffusivity in the bilateral uncinate fasciculus were significantly greater for patients with AD than for controls. There was no significant difference in diffusion anisotropy or diffusivity along Meyer's loop between the 2 groups. There was no significant difference in the number of voxels included in all constructed tracts between patients with AD and controls.

Conclusion: White matter tracts of the temporal stem can be evaluated independently by using diffusion tensor tractography, which appears to be a promising technique for determining changes in white matter in degenerative diseases.

Fig 1.

Tractographies were drawn by using diffusion-weighted images (EPI imaging: TR/TE, 2300/122 ms; b = 1000 seconds/mm²; 6-axis encoding; FOV, 230 mm; matrix, 128 × 128; section spacing, 3.3 mm; section thickness, 3 mm; averaging, 6). Tractographies of the inferior occipitofrontal fasciculus (green), uncinate fasciculus (blue), and Meyer’s loop (yellow are shown). A, 3D view from the right upper; B, view from the bottom; C, view from the right; D, view from the front. Mean FA and ADC values were measured along these tracts of interest separately.

Fig 2.

Comparison of mean FA, ADC, and number of voxels between patients with AD and controls. The patients with AD had significantly lower mean FA than the controls at both sides of the uncinate fasciculus and at the left side of the inferior occipitofrontal fasciculus (A). The patients with AD had significantly higher mean ADC than the controls at both sides of the uncinate fasciculus and inferior occipitofrontal fasciculus (B). There were no statistically significant differences between AD and controls for the number of voxels of the 3 tracts (C). R indicates right side; L, left side.