Single-orientation Quantitative Susceptibility Mapping identifies the Ventral Intermediate Nucleus of the Thalamus

Introduction: The ventral intermediate nucleus (VIM) represents the primary target in the treatment of tremor. Accurate localization is extremely important given its proximity to other thalamic nuclei. We utilized single orientation quantitative susceptibility mapping (QSM) at 3T to directly visualize the VIM. Methods: Four adult volunteers, one adult cadaver, and an essential tremor patient were scanned on a 3T MRI using a multi-echo gradient echo sequence. QSM images were generated using the improved sparse linear equation and least-squares (iLSQR) algorithm. Two adult subjects underwent multiple head orientation imaging for multi-orientation QSM reconstruction. The VIM was prospectively identified with direct visualization as well as indirect landmark-based localization. Results: The bilateral VIM was consistently identified as a hypointense structure within the lateral thalamus, appearing similar on multi-orientation and single-orientation QSM, corresponding to the myelinated dentatorubrothalamic tract (DRTT). The indirect method resulted in a comparatively inferomedial localization, at times missing the VIM and DRTT. Conclusion: Single-orientation QSM offers a clinically feasible, non-invasive imaging-based approach to directly localize the VIM.

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Thalamic organization in essential tremor patients with neuropathy: implication for functional neurosurgery

10.1101/2021.02.21.21251847 ◽

2021 ◽

Author(s):

Francesco Sammartino ◽

Vinayak Narayan ◽

Barbara Changizi ◽

Aristide Merola ◽

Vibhor Krishna

Keyword(s):

Deep Brain Stimulation ◽

Essential Tremor ◽

Clinical Outcomes ◽

Brain Stimulation ◽

Element Model ◽

Target Coverage ◽

Thalamic Nuclei ◽

Intermediate Nucleus ◽

Ventral Intermediate Nucleus ◽

Deep Brain

AbstractBackgroundMechanisms underlying the suboptimal effect of ventral intermediate nucleus deep brain stimulation in patients with essential tremor and co-morbid peripheral neuropathy remain unclear.ObjectivesWe compared disease-related (location and extension of the ventral intermediate nucleus) and surgery-related (targeting, intraoperative testing) factors in essential tremor patients with and without peripheral polyneuropathy treated with deep brain stimulation of the ventral intermediate nucleus, testing whether the overlap between volume of tissue activated and ventral intermediate nucleus (target coverage) was associated with clinical outcomes.MethodsPreoperative diffusion magnetic resonance imaging was used for thalamic segmentation, based on preferential cortical connectivity. The target coverage was estimated using a finite element model. Tremor severity was scored at rest, posture, action, and handwriting at baseline, 6, and 12 months. Tremor improvement <50% at 12 months was deemed suboptimal. Vertex-wise shape analysis and edge analysis were performed to compare the ventral intermediate nucleus location and extension.Results9.7% (18/185) of essential tremor patients treated with deep brain stimulation had co-morbid polyneuropathy. These patients showed a more medial (p=0.03) and anterior (p=0.04) location of the ventral intermediate nucleus, lower target coverage (p=0.049), and worse clinical outcomes (p=0.006) compared to those without polyneuropathy. No differences were observed in the volume of tissue activated between the two groups. Optimal clinical outcomes were associated with greater target coverage (optimal coverage >48%).ConclusionsIn essential tremor, co-morbid polyneuropathy may result in suboptimal deep brain stimulation outcomes and lower target coverage, likely related to a reorganization of the ventral thalamic nuclei.

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Automatic Ventral Intermediate Nucleus Localization Based on Anterior Commissure and Posterior Commissure

10.21203/rs.3.rs-19214/v2 ◽

2020 ◽

Author(s):

Riyanarto Sarno ◽

Kelly Rossa Sungkono ◽

Mohammad Ardika Rifqi ◽

Achmad Fahmi ◽

Agus Turchan ◽

...

Keyword(s):

Anterior Commissure ◽

Brain Lesion ◽

Three Dimensional ◽

Average Error ◽

Thalamic Nuclei ◽

Posterior Commissure ◽

Indirect Methods ◽

Intermediate Nucleus ◽

Neurosurgical Planning ◽

Ventral Intermediate Nucleus

Abstract The ventral intermediate nucleus (Vim), as the motor thalamic nuclei section, is a generally used target in brain lesion surgery or stimulation for decreasing tremors in people with Parkinson’s disease. Determining the exact position of Vim is challenging because Vim cannot be visualized clearly in commonly used magnetic resonance imaging (MR). Indirect methods, i.e., Coordinate-based targeting and Guiot’s, utilize anterior commissure and posterior commissure to detect the location of Vim. In practice, neurosurgeons manually implement these methods in existing neurosurgical planning software, so the accuracy of the targeting depends on their memory and foresight. Afterward, Coordinate-based targeting and Guiot’s locate Vim based on anterior commissure (AC) and posterior commissure (PC), so neurosurgeons must correctly determine AC and PC. This paper proposes automatic indirect methods and measures the accuracy of indirect methods in MRIs with correct and incorrect orientations of AC-PC planes. An objective of analyzing indirect methods in MRIs with incorrect orientations of AC-PC planes is to discover the most resilient indirect method with inaccuracy AC-PC planes. To develop automatic indirect methods, the first step is redefining the plane passing through three defined points, i.e., AC, PC, and midline reference, by a quaternion. Secondly, Coordinate-based targeting and Guiot’s are implemented to determine the Vim targeting location automatically. This paper converts the rules of those methods in voxels because the rules use millimeters while the three-dimensional MRIs use voxels. The experiment shows that Vim locations obtained by Guiot’s are more accurate than those by Coordinate-based targeting in MRIs with the correct orientation of AC-PC planes. Guiot’s has 0.05 mm smaller value of average error results than Coordinate-based targeting. In contrast, Vim locations based on Coordinate-based targeting are more accurate in the MRIs with the incorrect orientation of AC-PC planes. Coordinate-based targeting has 0.032 mm smaller value of average error results than Guiot’s.

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