Tag: ventral intermediate nucleus

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A novel high-precision fiber tractography for nuclear localization in transcranial magnetic resonance–guided focused ultrasound surgery

J Neurosurg 140:1471–1481, 2024

In transcranial MR-guided focused ultrasound (TcMRgFUS), fiber tractography using diffusion tensor imaging (DTI) has been proposed as a direct method to identify the ventral intermediate nucleus (Vim), the ventral caudal nucleus (Vc), and the pyramidal tract (PT). However, the limitations of the DTI algorithm affect the accuracy of visualizing anatomical structures due to its low-quality fiber tractography, whereas the application of the generalized q-sampling imaging (GQI) algorithm enables the visualization of high-quality fiber tracts, offering detailed insights into the spatial distribution of motor cortex fibers. This retrospective study aimed to investigate the usefulness of high-precision fiber tractography using the GQI algorithm as a planning image in TcMRgFUS to achieve favorable clinical outcomes.

METHODS This study included 20 patients who underwent TcMRgFUS. The Clinical Rating Scale for Tremor (CRST) scores and MR images were evaluated pretreatment and at 24 hours and 3–6 months after treatment. Cases were classified based on the presence and adversity of adverse events (AEs): no AEs, mild AEs without additional treatment, and severe AEs requiring prolonged hospitalization. Fiber tractography of the Vim, Vc, and PT was visualized using the DTI and GQI algorithm. The overlapping volume between Vim fibers and the lesion was measured, and correlation analysis was performed. The relationship between AEs and the overlapping volume of the Vc and PT fibers within the lesions was examined. The cutoff value to achieve a favorable clinical outcome and avoid AEs was determined using receiver operating characteristic curve analysis.

RESULTS All patients showed improvement in tremors 24 hours after treatment, with 3 patients experiencing mild AEs and 1 patient experiencing severe AEs. At the 3- to 6-month follow-up, 5 patients experienced recurrence, and 2 patients had persistent mild AEs. Although fiber visualization in the motor cortex using the DTI algorithm was insufficient, the GQI algorithm enabled the visualization of significantly higher-quality fibers. A strong correlation was observed between the overlapping volume that intersects the lesion and Vim fibers and the degree of tremor improvement (r = 0.72). Higher overlapping volumes of Vc and PT within the lesion were associated with an increased likelihood of AEs (p < 0.05); the cutoff volume of Vim fibers within the lesion for a favorable clinical outcome was 401 mm 3 , while the volume of Vc and PT within the lesion to avoid AEs was 99 mm 3 .

CONCLUSIONS This pilot study suggests that incorporating the high-precision GQI algorithm for fiber tractography as a planning imaging technique for TcMRgFUS has the potential to enhance targeting precision and achieve favorable clinical outcomes.

 

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Tractography-Based Surgical Targeting for Thalamic Deep Brain Stimulation: A Comparison of Probabilistic vs Deterministic Fiber Tracking of the Dentato-Rubro-Thalamic Tract

Neurosurgery 90:419–425, 2022

The ventral intermediate (VIM) thalamic nucleus is the main target for the surgical treatment of refractory tremor. Initial targeting traditionally relies on atlas-based stereotactic targeting formulas, which only minimally account for individual anatomy. Al- ternative approaches have been proposed, including direct targeting of the dentato-rubro- thalamic tract (DRTT), which, in clinical settings, is generally reconstructed with deterministic tracking. Whether more advanced probabilistic techniques are feasible on clinical-grade magnetic resonance acquisitions and lead to enhanced reconstructions is poorly understood.

OBJECTIVE: To compare DRTT reconstructed with deterministic vs probabilistic tracking. METHODS: Thisisaretrospectivestudyof19patientswithessentialtremorwhounderwentdeep brain stimulation (DBS) with intraoperative neurophysiology and stimulation testing. We assessed the proximity of the DRTT to the DBS lead and to the active contact chosen based on clinical response.

RESULTS: In the commissural plane, the deterministic DRTT was anterior (P<104)and  < 104) to the DBS lead. By contrast, although the probabilistic DRTT was also anterior to the lead (P < 104), there was no difference in the mediolateral dimension (P = .5). Moreover, the 3- dimensional Euclidean distance from the active contact to the probabilistic DRTT was smaller vs the distance to the deterministic DRTT (3.32 ± 1.70 mm vs 5.01 ± 2.12 mm; P < 104).

CONCLUSION: DRTT reconstructed with probabilistic fiber tracking was superior in spatial proximity to the physiology-guided DBS lead and to the empirically chosen active contact. These data inform strategies for surgical targeting of the VIM.

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Direct targeting of the ventral intermediate nucleus of the thalamus in deep brain stimulation for essential tremor

J Neurosurg 136:662–671, 2022

The ventral intermediate nucleus of the thalamus (VIM) is an effective target for deep brain stimulation (DBS) to control symptoms related to essential tremor. The VIM is typically targeted using indirect methods, although studies have reported visualization of the VIM on proton density–weighted MRI. This study compares the outcomes between patients who underwent VIM DBS with direct and indirect targeting.

METHODS Between August 2013 and December 2019, 230 patients underwent VIM DBS at the senior author’s institution. Of these patients, 92 had direct targeting (direct visualization on proton density 3-T MRI). The remaining 138 patients had indirect targeting (relative to the third ventricle and anterior commissure–posterior commissure line).

RESULTS Coordinates of electrodes placed with direct targeting were significantly more lateral (p < 0.001) and anterior (p < 0.001) than those placed with indirect targeting. The optimal stimulation amplitude for devices measured in voltage was lower for those who underwent direct targeting than for those who underwent indirect targeting (p < 0.001). Patients undergoing direct targeting had a greater improvement only in their Quality of Life in Essential Tremor Questionnaire hobby score versus those undergoing indirect targeting (p = 0.04). The direct targeting group had substantially more symptomatic hemorrhages than the indirect targeting group (p = 0.04). All patients who experienced a postoperative hemorrhage after DBS recovered without intervention.

CONCLUSIONS Patients who underwent direct VIM targeting for DBS treatment of essential tremor had similar clinical outcomes to those who underwent indirect targeting. Direct VIM targeting is safe and effective.

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