Use of probabilistic tractography to provide reliable distinction of the motor and sensory thalamus for prospective targeting during asleep deep brain stimulation

Abstract

OBJECTIVE Accurate electrode placement is key to effective deep brain stimulation (DBS). The ventral intermediate nucleus (VIM) of the thalamus is an established surgical target for the treatment of essential tremor (ET). Retrospective tractography-based analysis of electrode placement has associated successful outcomes with modulation of motor input to VIM, but no study has yet evaluated the feasibility and efficacy of prospective presurgical tractography-based targeting alone. Therefore, the authors sought to demonstrate the safety and efficacy of probabilistic tractography–based VIM targeting in ET patients and to perform a systematic comparison of probabilistic and deterministic tractography. METHODS Fourteen patients with ET underwent preoperative diffusion imaging. Probabilistic tractography was applied for preoperative targeting, and deterministic tractography was performed as a comparison between methods. Tractography was performed using the motor and sensory areas as initiation seeds, the ipsilateral thalamus as an inclusion mask, and the contralateral dentate nucleus as a termination mask. Tract-density maps consisted of voxels with 10% or less of the maximum intensity and were superimposed onto anatomical images for presurgical planning. Target planning was based on probabilistic tract-density images and indirect target coordinates. Patients underwent robotic image-guided, image-verified implantation of directional DBS systems. Postoperative tremor scores with and without DBS were recorded. The center of gravity and Dice similarity coefficients were calculated and compared between tracking methods. RESULTS Prospective probabilistic targeting of VIM was successful in all 14 patients. All patients experienced significant tremor reduction. Formal postoperative tremor scores were available for 9 patients, who demonstrated a mean 68.0% tremor reduction. Large differences between tracking methods were observed across patients. Probabilistic tractography–identified VIM fibers were more anterior, lateral, and superior than deterministic tractography–identified fibers, whereas probabilistic tractography–identified ventralis caudalis fibers were more posterior, lateral, and superior than deterministic tractography–identified fibers. Deterministic methods were unable to clearly distinguish between motor and sensory fibers in the majority of patients, but probabilistic methods produced distinct separation. CONCLUSIONS Probabilistic tractography–based VIM targeting is safe and effective for the treatment of ET. Probabilistic tractography is more precise than deterministic tractography for the delineation of VIM and the ventralis caudalis nucleus of the thalamus. Deterministic algorithms tended to underestimate separation between motor and sensory fibers, which may have been due to its limitations with crossing fibers. Larger studies across multiple centers are necessary to further validate this method.

Effect of Enlarged Perivascular Spaces in Reliable Distinction of Prospective Targeting During Deep Brain Stimulation in Patients With Advanced Parkinson's Disease: A Study of Deterministic and Probabilistic Tractography

“…Stimulation focused on motor network subregions of BG nuclei is associated with favorable outcomes after DBS for movement disorders. 14,33 In this study, the motor regions of the GPi and STN in patients selected for DBS were outlined using deterministic and probabilistic fiber tracking techniques. This study partially replicates previous work performed by Muller et al, 5 where both deterministic and probabilistic tractography methods were engaged to delineate corticopallidal and corticosubthalamic pathways.…”

“…5,12,13 Probabilistic tractography has even been shown to be able to refine DBS targeting of the ventralis intermedius nucleus (Vim) of the thalamus in patients with essential tremor. 14 Perivascular spaces (PVSs), also known as Virchow-Robin spaces, are fluid-filled spaces accompanying vessels in the cerebral cortex. They act as conduits for fluid transport and exchange between cerebrospinal fluid (CSF) and interstitial fluid (ISF) as part of the avital waste clearance network referred to as the "glymphatic system."…”

“…5,12,13 Probabilistic tractography has even been shown to be able to refine DBS targeting of the ventralis intermedius nucleus (Vim) of the thalamus in patients with essential tremor. 14…”

Multi‐atlas thalamic nuclei segmentation on standard T1‐weighed MRI with application to normal aging

“…Selective thalamic sites like the ventral intermediate (VIM) nucleus are also targets for deep brain stimulation for relief of intractable tremor and other impairments of motor control. The occasional success of noninvasive treatments like transcranial magnetic stimulation for Mild Cognitive Impairment (MCI) (Elder & Taylor, 2014 ) or hand tremor (Muller et al, 2021 ), neurosurgical interventions, or deep brain stimulation (DBS) for motor control impairment highlight the need to develop imaging protocols with spatial precision for therapeutic targeting.…”

Robot-Assisted Minimally Invasive Asleep Single-Stage Deep Brain Stimulation Surgery: Operative Technique and Systematic Review

“…5-7 Recent advances in imaging, such as higher resolution MRI and diffusion-based tractography, have allowed for direct targeting methods and image-verified DBS under general anesthesia (GA). 4-11…”