Multitensor tractography enables better depiction of motor pathways: initial clinical experience using diffusion-weighted MR imaging with standard b-value

Abstract

Background and purpose: The purpose of this work was to test the feasibility of using high angular resolution diffusion imaging (HARDI)-based multitensor tractography to depict motor pathways in patients with brain tumors.

Materials and methods: Ten patients (6 males and 4 females) with a mean age of 52 years (range, 9-77 years) were scanned using a 1.5T clinical MR unit. Single-shot echo-planar imaging was used for diffusion-weighted imaging (repetition time, 6000 ms; excitation time, 88 ms) with a diffusion-sensitizing gradient in 32 orientations and a b-value of 1000 s/mm(2). Data postprocessing was performed using both the conventional single- and multitensor methods. The depiction rate of the 5 major components of the motor pathways, that is, the lower extremity, trunk, hand, face, and tongue, was assessed.

Results: Motor fibers on both lesional and contralesional sides were successfully depicted by both the single-tensor and multitensor techniques. However, with the single-tensor model, the depiction of motor pathways was typically limited to the fibers of trunk areas. With the multitensor technique, at least 4 of 5 major fiber bundles arising from the primary motor cortex could be identified.

Conclusion: HARDI-based multitensor tractography using a standard b-value (1000 s/mm(2)) can depict the fiber tracts from the face and tongue regions of the primary motor cortex.

Fig 1.

ROIs were placed at 5 different locations along the primary motor cortex to depict the different fiber tracts of the pyramidal tract. The brain stem ROI is indicated by the arrows.

Fig 2.

The relative number of points constituting each fiber bundle in the contralesional hemisphere are shown. For example, by using tensor-based tractography, case 1 had mostly trunk fibers depicted (97%) and a low percentage (3%) of LE fibers. On the other hand, by using the multitensor technique, the fibers from other parts are also depicted, and, in this particular case, the trunk fibers constitute only 23% of all fibers. Of note, in general the multitensor approach is able to depict fibers from various locations, whereas the single-tensor approach is limited to the depiction of the trunk and hand regions.

Fig 3.

The relative number of points constituting each fiber bundle in the lesional hemisphere is shown. Of note, the depiction of the fibers in this hemisphere is largely limited to the trunk fibers when the single-tensor approach is used. The difference between the single-tensor technique and the multitensor technique becomes obvious in the lesional hemisphere.

Fig 4.

A 55-year-old man (case 4) presented to the hospital with a Jacksonian seizure starting in his right fingers. On MR imaging, a large left frontal lobe tumor was depicted. Of note, the multitensor technique is able to depict fibers from various locations and is able to reveal the relationship between the vital fiber tracts and the dorsal edge of the tumor. On the transaxial view, note that single-tensor tractography is able to show that the trunk fibers (purple) are located within the tumor. Using the multitensor approach, one can see that the hand fibers (green) are involved. Facial fibers (blue) are also seen in close proximity to the tumor.

Fig 5.

A 58-year-old woman with glioblastoma multiforme (case 1) is illustrated. A large right parietal lobe tumor is noted with surrounding vasogenic edema. Note that the pyramidal fibers of lesional side (right) are not depicted using single-tensor tractography, whereas they are well shown by using multitensor tractography. These fibers are noted to have substantial anterior displacement.