A role of diffusion tensor imaging in movement disorder surgery

Abstract

The safe and reversible nature of deep brain stimulation (DBS) has allowed movement disorder neurosurgery to become commonplace throughout the world. Fundamental understanding of individual patient's anatomy is critical for optimizing the effects and side effects of DBS surgery. Three patients undergoing stereotactic surgery for movement disorders, at the institution's intraoperative magnetic resonance imaging operating suite, were studied with fiber tractography. Stereotactic targets and fiber tractography were determined on preoperative magnetic resonance imagings using the Schaltenbrand-Wahren atlas for definition in the BrainLab iPlan software (BrainLAB Inc., Feldkirchen, Germany). Subthalamic nucleus, globus pallidus interna, and ventral intermediate nucleus targets were studied. Diffusion tensor imaging parameters used ranged from 2 to 8 mm for volume of interest in the x/y/z planes, fiber length was kept constant at 30 mm, and fractional anisotropy threshold varied from 0.20 to 0.45. Diffusion tensor imaging tractography allowed reliable and reproducible visualization and correlation between frontal eye field, premotor, primary motor, and primary sensory cortices via corticospinal tracts and corticopontocerebellar tracts. There is an apparent increase in the number of cortical regions targeted by the fiber tracts as the region of interest is enlarged. This represents a possible mechanism of the increased effects and side effects observed with higher stimulation voltages. Currently available diffusion tensor imaging techniques allow potential methods to characterize the effects and side effects of DBS. This technology has the potential of being a powerful tool to optimize DBS neurosurgery.

Fig. 1

a Diagram of the Medtronic 3389 intracranial DBS lead orientation and measurements. b Color-coded diagram of ROI voxels used for fiber tractography at specific locations surrounding the case electrode lead. The yellow boxes demonstrate the 2 × 2 × 2 mm small ROIs. The purple boxes demonstrate the total of 2 × 2 × 8 mm large ROI (including the original 2 × 2 × 2 mm ROI). Fiber tractography demonstrated in Figs. 3–5 adhere to this color scheme

Fig. 2

Three-dimensional demonstration of fiber tractography with STN, VIM, and GPi targets in anteroposterior (a), craniocaudal (b), and lateral (c) views. The ROI was a 4-mm cube centered around the targets as calculated from the AC/PC coordinates. There is significant variability in fiber tract targets, particularly between GPi and STN DBS targets

Fig. 3

Fiber tractography of lead 1 in patient 1 (STN DBS). Three-dimensional depiction (a) of the small (yellow) and large (purple) ROIs demonstrating increased cortical fiber tract targets. The pink object is the primary motor cortex (based on anatomical landmarks). Axial (b) and coronal (c, d) slices of source images with color-coded diagrams depict the large ROI fiber tracts (purple—arrows) extending to the prefrontal and parietal cortices, possibly including the frontal eye fields in addition to the fiber tracts of the small ROI (yellow—arrowheads). The pink region is the motor cortex region

Fig. 4

Fiber tractography of lead 0 in patient 2 (VIM DBS). Three-dimensional depiction (a) of the small (yellow) and large (purple) ROIs demonstrating increased cortical fiber tract targets. The pink object is the primary motor cortex (based on anatomical landmarks). Axial (b) and coronal (c, d) slices of source images with color-coded diagrams depict the large ROI fiber tracts (purple—arrows) extending to the prefrontal and parietal cortices in addition to the fiber tracts of the small ROI (yellow—arrowhead)

Fig. 5

Fiber tractography of lead 0 in patient 3 (GPi DBS). Three-Dimensional depiction (a) of the small (yellow) and large (purple) ROIs demonstrating increased cortical fiber tract targets. The pink object is the primary motor cortex (based on anatomical landmarks). Coronal (b) and axial (c, d) slices of source images with color-coded diagrams depict the large ROI fiber tracts (purple—arrows) extending to the prefrontal cortex, possibly including the frontal eye fields in addition to the fiber tracts of the small ROI (yellow—arrowheads)