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Feasibility of Diffusion Tractography for the Reconstruction of Intra-Thalamic and Cerebello-Thalamic Targets for Functional Neurosurgery: A Multi-Vendor Pilot Study in Four Subjects.

Jakab A, Werner B, Piccirelli M, Kovács K, Martin E, Thornton JS, Yousry T, Szekely G, O'Gorman Tuura R - Front Neuroanat (2016)

Bottom Line: While CTT resolved the anatomically correct trajectory of the tract individually, high volumetric variability was found across subjects and between scanners.DTI can be applied in the clinical, preoperative setting to reconstruct the CTT and to localize subdivisions within the lateral thalamus.In our pilot study, such subdivisions moderately matched the borders of the ventrolateral-posteroventral (VLpv) nucleus and the ventral-posterolateral (VPL) nucleus.

View Article: PubMed Central - PubMed

Affiliation: Center for Magnetic Resonance Imaging Research, University Children's HospitalZürich, Switzerland; Computational Imaging Research Lab, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of ViennaVienna, Austria.

ABSTRACT
Functional stereotactic neurosurgery by means of deep brain stimulation or ablation provides an effective treatment for movement disorders, but the outcome of surgical interventions depends on the accuracy by which the target structures are reached. The purpose of this pilot study was to evaluate the feasibility of diffusion tensor imaging (DTI) based probabilistic tractography of deep brain structures that are commonly used for pre- and perioperative targeting for functional neurosurgery. Three targets were reconstructed based on their significance as intervention sites or as a no-go area to avoid adverse side effects: the connections propagating from the thalamus to (1) primary and supplementary motor areas, (2) to somatosensory areas and the cerebello-thalamic tract (CTT). We evaluated the overlap of the reconstructed connectivity based targets with corresponding atlas based data, and tested the inter-subject and inter-scanner variability by acquiring repeated DTI from four volunteers, and on three MRI scanners with similar sequence parameters. Compared to a 3D histological atlas of the human thalamus, moderate overlaps of 35-50% were measured between connectivity- and atlas based volumes, while the minimal distance between the centerpoints of atlas and connectivity targets was 2.5 mm. The variability caused by the MRI scanner was similar to the inter-subject variability, except for connections with the postcentral gyrus where it was higher. While CTT resolved the anatomically correct trajectory of the tract individually, high volumetric variability was found across subjects and between scanners. DTI can be applied in the clinical, preoperative setting to reconstruct the CTT and to localize subdivisions within the lateral thalamus. In our pilot study, such subdivisions moderately matched the borders of the ventrolateral-posteroventral (VLpv) nucleus and the ventral-posterolateral (VPL) nucleus. Limitations of the currently used standard DTI protocols were exacerbated by large scanner-to-scanner variability of the connectivity-based targets.

No MeSH data available.


Related in: MedlinePlus

Optimization of the connectivity threshold applied to connectivity based intrathalamic targets.(A) Inter-subject overlap as a function of the applied connectivity threshold; (B) overlap with anatomical atlas as a function of the applied connectivity threshold; (C) determining the population-level optimal threshold value as a maximum point of the function.
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Figure 4: Optimization of the connectivity threshold applied to connectivity based intrathalamic targets.(A) Inter-subject overlap as a function of the applied connectivity threshold; (B) overlap with anatomical atlas as a function of the applied connectivity threshold; (C) determining the population-level optimal threshold value as a maximum point of the function.

Mentions: Our results suggest that while the agreement with the atlas targets is higher if the connectivity threshold is increased (for example, a maximum is seen in Figure 3C at the 90th percentile threshold), the inter-subject reproducibility was decreased at larger connectivity thresholds. Therefore, it was necessary to determine a consensual cut-off value which represents a trade-off between the two feasibility metrics. First, we investigated the effect of connectivity probability thresholding on the expected reproducibility of CBT maps. The lower the connectivity threshold, the higher the inter-subject overlap (Figure 4A). This means, however, that the CBTs become less specific for the given neurosurgical target: as the connectivity threshold values converge to zero, almost the entire thalamus is included as a potential target volume, which is anatomically incorrect. In order to find the optimal connectivity-based threshold, representing a compromise between larger inter-subject reproducibility and larger overlap with the atlas target, we multiplied the two overlap metrics and located the maximum value of this combined metric (Figure 4). To provide a consensual value, we multiplied the median values of population-overlaps and the median values of the correspondence to the anatomical atlas. In a similar manner as for the overlap with the anatomical target (Figure 4B), the consensus metric also had a maximum, which was used to determine the optimal cut-off value (Figure 4C).


Feasibility of Diffusion Tractography for the Reconstruction of Intra-Thalamic and Cerebello-Thalamic Targets for Functional Neurosurgery: A Multi-Vendor Pilot Study in Four Subjects.

Jakab A, Werner B, Piccirelli M, Kovács K, Martin E, Thornton JS, Yousry T, Szekely G, O'Gorman Tuura R - Front Neuroanat (2016)

Optimization of the connectivity threshold applied to connectivity based intrathalamic targets.(A) Inter-subject overlap as a function of the applied connectivity threshold; (B) overlap with anatomical atlas as a function of the applied connectivity threshold; (C) determining the population-level optimal threshold value as a maximum point of the function.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940380&req=5

Figure 4: Optimization of the connectivity threshold applied to connectivity based intrathalamic targets.(A) Inter-subject overlap as a function of the applied connectivity threshold; (B) overlap with anatomical atlas as a function of the applied connectivity threshold; (C) determining the population-level optimal threshold value as a maximum point of the function.
Mentions: Our results suggest that while the agreement with the atlas targets is higher if the connectivity threshold is increased (for example, a maximum is seen in Figure 3C at the 90th percentile threshold), the inter-subject reproducibility was decreased at larger connectivity thresholds. Therefore, it was necessary to determine a consensual cut-off value which represents a trade-off between the two feasibility metrics. First, we investigated the effect of connectivity probability thresholding on the expected reproducibility of CBT maps. The lower the connectivity threshold, the higher the inter-subject overlap (Figure 4A). This means, however, that the CBTs become less specific for the given neurosurgical target: as the connectivity threshold values converge to zero, almost the entire thalamus is included as a potential target volume, which is anatomically incorrect. In order to find the optimal connectivity-based threshold, representing a compromise between larger inter-subject reproducibility and larger overlap with the atlas target, we multiplied the two overlap metrics and located the maximum value of this combined metric (Figure 4). To provide a consensual value, we multiplied the median values of population-overlaps and the median values of the correspondence to the anatomical atlas. In a similar manner as for the overlap with the anatomical target (Figure 4B), the consensus metric also had a maximum, which was used to determine the optimal cut-off value (Figure 4C).

Bottom Line: While CTT resolved the anatomically correct trajectory of the tract individually, high volumetric variability was found across subjects and between scanners.DTI can be applied in the clinical, preoperative setting to reconstruct the CTT and to localize subdivisions within the lateral thalamus.In our pilot study, such subdivisions moderately matched the borders of the ventrolateral-posteroventral (VLpv) nucleus and the ventral-posterolateral (VPL) nucleus.

View Article: PubMed Central - PubMed

Affiliation: Center for Magnetic Resonance Imaging Research, University Children's HospitalZürich, Switzerland; Computational Imaging Research Lab, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of ViennaVienna, Austria.

ABSTRACT
Functional stereotactic neurosurgery by means of deep brain stimulation or ablation provides an effective treatment for movement disorders, but the outcome of surgical interventions depends on the accuracy by which the target structures are reached. The purpose of this pilot study was to evaluate the feasibility of diffusion tensor imaging (DTI) based probabilistic tractography of deep brain structures that are commonly used for pre- and perioperative targeting for functional neurosurgery. Three targets were reconstructed based on their significance as intervention sites or as a no-go area to avoid adverse side effects: the connections propagating from the thalamus to (1) primary and supplementary motor areas, (2) to somatosensory areas and the cerebello-thalamic tract (CTT). We evaluated the overlap of the reconstructed connectivity based targets with corresponding atlas based data, and tested the inter-subject and inter-scanner variability by acquiring repeated DTI from four volunteers, and on three MRI scanners with similar sequence parameters. Compared to a 3D histological atlas of the human thalamus, moderate overlaps of 35-50% were measured between connectivity- and atlas based volumes, while the minimal distance between the centerpoints of atlas and connectivity targets was 2.5 mm. The variability caused by the MRI scanner was similar to the inter-subject variability, except for connections with the postcentral gyrus where it was higher. While CTT resolved the anatomically correct trajectory of the tract individually, high volumetric variability was found across subjects and between scanners. DTI can be applied in the clinical, preoperative setting to reconstruct the CTT and to localize subdivisions within the lateral thalamus. In our pilot study, such subdivisions moderately matched the borders of the ventrolateral-posteroventral (VLpv) nucleus and the ventral-posterolateral (VPL) nucleus. Limitations of the currently used standard DTI protocols were exacerbated by large scanner-to-scanner variability of the connectivity-based targets.

No MeSH data available.


Related in: MedlinePlus