Fibre-Orientation-based Contrast for Thalamic Subnuclei Targeting using MR-guided Focused Ultrasound
Poster No:
1295
Submission Type:
Abstract Submission
Authors:
Eric Pierre1, Chris Kokkinos1, Wesley Thevathasan2,3, Kristian Bulluss4,3,5, Arthur Thevathasan2,3, Robert Smith1,3, David Vaughan1,3, David Abbott1,3, Heath Pardoe1,3, Graeme Jackson1,3
Institutions:
1The Florey Institute of Neuroscience and Mental Health, Melbourne, Australia, 2Department of Neurology, Austin Health, Melbourne, Australia, 3The University of Melbourne, Melbourne, Australia, 4Department of Neurosurgery, Austin Health, Melbourne, Australia, 5Department of Neurosurgery, St Vincent’s Hospital, Melbourne, Australia
First Author:
Co-Author(s):
Wesley Thevathasan
Department of Neurology, Austin Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Department of Neurology, Austin Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Kristian Bulluss
Department of Neurosurgery, Austin Health|The University of Melbourne|Department of Neurosurgery, St Vincent’s Hospital
Melbourne, Australia|Melbourne, Australia|Melbourne, Australia
Department of Neurosurgery, Austin Health|The University of Melbourne|Department of Neurosurgery, St Vincent’s Hospital
Melbourne, Australia|Melbourne, Australia|Melbourne, Australia
Arthur Thevathasan
Department of Neurology, Austin Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Department of Neurology, Austin Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Robert Smith
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
David Vaughan
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
David Abbott, PhD
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Heath Pardoe, PhD
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Graeme Jackson
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
The Florey Institute of Neuroscience and Mental Health|The University of Melbourne
Melbourne, Australia|Melbourne, Australia
Introduction:
The major target for MR-guided Focused Ultrasound (MRgFUS) for treatment of essential tremor (ET) is the ventral intermediate nucleus (Vim) of the thalamus. Accurate MRI visualization of the Vim is still an active topic of research (Jameel et al., 2024).
Most proposed methods include structural MRI techniques like susceptibility-weighted imaging (Abosch et al., 2010), quantitative susceptibility mapping (Deistung et al., 2013), or white-matter nulled T1 imaging, e.g. FGATIR (Sudhyadhom et al., 2009). Other approaches make use of Diffusion-Weighted Imaging (DWI) to probe the thalamic microstructure, e.g. via tractography (Tian et al., 2018).
To circumvent the usual drawbacks of tractography, a combination of both approaches has been recently proposed to produce a synthetic FAT1 contrast, based on high-resolution T1-weighted images and DWI metrics (Goedemans et al., 2024).
However, DWI methods proposed thus far rely on tensor-based analysis for probing fibre-bundle orientation, with known modelling limits. This work applies more modern DWI techniques to represent fibre bundles within voxels (Jeurissen et al., 2014), combined with structural contrast for enhanced visualization of Thalamic microstructure.
Most proposed methods include structural MRI techniques like susceptibility-weighted imaging (Abosch et al., 2010), quantitative susceptibility mapping (Deistung et al., 2013), or white-matter nulled T1 imaging, e.g. FGATIR (Sudhyadhom et al., 2009). Other approaches make use of Diffusion-Weighted Imaging (DWI) to probe the thalamic microstructure, e.g. via tractography (Tian et al., 2018).
To circumvent the usual drawbacks of tractography, a combination of both approaches has been recently proposed to produce a synthetic FAT1 contrast, based on high-resolution T1-weighted images and DWI metrics (Goedemans et al., 2024).
However, DWI methods proposed thus far rely on tensor-based analysis for probing fibre-bundle orientation, with known modelling limits. This work applies more modern DWI techniques to represent fibre bundles within voxels (Jeurissen et al., 2014), combined with structural contrast for enhanced visualization of Thalamic microstructure.
Methods:
Three patients undergoing MRgFUS ablation for ET underwent scanning on a Siemens 3T Vida Scanner for pre-operative planning and 1-day post-operation. Acquisitions included a T1-weighted and FGATIR volume at 1mm isotropic resolution, and a DWI dataset of 105 directions over b-values (0, 1000 & 3000 s/mm²) at 2mm resolution, interpolated to 1.3mm in-plane. The clinical team used FGATIR images for final Vim targeting and was blinded to the DWI data.
DWI preprocessing included denoising, Gibbs ringing removal, distortion & motion correction. Fibre Orientation Distributions (FODs) were computed from the DWI dataset using MRtrix3 software (Tournier et al., 2019). FAT1 contrast was also computed for comparison (Figure 1).
For each voxel, we averaged the FOD peak of all fibre populations, weighted by their apparent fibre density. The resulting average peak was given a direction-encoded colour, with intensity corresponding to the averaged peak's height. The average fibre direction map was overlayed onto the FGATIR volume.
Thalamic subnuclei were manually segmented according to Schaltenbrand and Morel atlas references (Najdenovska et al. 2018). The day-1 post-operative T1-weighted volume was registered to the pre-operative planning FGATIR. An ROI of the necrotic core (Keil et al. 2020) was then segmented for lesion visualization.
DWI preprocessing included denoising, Gibbs ringing removal, distortion & motion correction. Fibre Orientation Distributions (FODs) were computed from the DWI dataset using MRtrix3 software (Tournier et al., 2019). FAT1 contrast was also computed for comparison (Figure 1).
For each voxel, we averaged the FOD peak of all fibre populations, weighted by their apparent fibre density. The resulting average peak was given a direction-encoded colour, with intensity corresponding to the averaged peak's height. The average fibre direction map was overlayed onto the FGATIR volume.
Thalamic subnuclei were manually segmented according to Schaltenbrand and Morel atlas references (Najdenovska et al. 2018). The day-1 post-operative T1-weighted volume was registered to the pre-operative planning FGATIR. An ROI of the necrotic core (Keil et al. 2020) was then segmented for lesion visualization.
Results:
The proposed overlay is in good agreement with known neuroanatomy (Figure 1). In the internal capsule, cortico-spinal tracts appear in strong blue (high fibre density in superior-inferior direction), and purple (left right + superior-inferior direction) with thalamic radiations. ventral thalamic nuclei are more lightly shaded (less axonal density) in red (anteriorly) and purple (posteriorly). Anterior and medial groups appear in strong green (anterior-posterior direction). The use of FGATIR signal provides better contrast of Ventral Subnuclei compared to FAT1.
Figure 2 shows subnuclei segmentations for all three patients, transformed to the FGATIR volumes, with the day-1 necrotic core ROI additionally highlighted. All ROIs were close to the Vim/Ventralis Caudalis (VC) border, in agreement with multi-centre studies (Jameel et al., 2024).
All three patients showed significant tremor reduction on the corresponding treated side and are awaiting tremor reduction assessment at 3- and 12-months follow-up post-surgery.
Figure 2 shows subnuclei segmentations for all three patients, transformed to the FGATIR volumes, with the day-1 necrotic core ROI additionally highlighted. All ROIs were close to the Vim/Ventralis Caudalis (VC) border, in agreement with multi-centre studies (Jameel et al., 2024).
All three patients showed significant tremor reduction on the corresponding treated side and are awaiting tremor reduction assessment at 3- and 12-months follow-up post-surgery.
Conclusions:
We demonstrate an MRI overlay technique based on FOD maps and FGATIR contrast to better visualize thalamic subnuclei. The proposed method shows good agreement with expected neuroanatomy and surgical outcomes. While the small sample size precludes statistical analysis, initial results suggest potential value for surgical planning in MRgFUS thalamotomy, warranting validation in larger cohorts.
Brain Stimulation:
Sonic/Ultrasound 2
Disorders of the Nervous System:
Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s)
Modeling and Analysis Methods:
Diffusion MRI Modeling and Analysis 1
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Subcortical Structures
Keywords:
Movement Disorder
MRI
Segmentation
STRUCTURAL MRI
Sub-Cortical
Thalamus
ULTRASOUND
1|2Indicates the priority used for review
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Provide references using APA citation style.
Deistung, A. (2013). Toward in vivo histology: a comparison of quantitative susceptibility mapping (QSM) with magnitude-, phase-, and R2*-imaging at ultra-high magnetic field strength. Neuroimage, 65, 299-314.
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Jameel, A. (2024). The evolution of ventral intermediate nucleus targeting in MRI guided focused ultrasound thalamotomy for essential tremor: an international multi center evaluation. Frontiers in Neurology, 15.
Jeurissen, B. (2014). Multi-tissue constrained spherical deconvolution for improved analysis of multi-shell diffusion MRI data. Neuroimage, 103, 411-426.
Keil, V.C. (2020). MRI follow-up after magnetic resonance-guided focused ultrasound for non-invasive thalamotomy: the neuroradiologist's perspective. Neuroradiology, 62(9), 1111-1122.
Najdenovska, E. (2018). In-vivo probabilistic atlas of human thalamic nuclei based on diffusion- weighted magnetic resonance imaging. Scientific Data, 5, 180270
Sudhyadhom, A. (2009). A high resolution and high contrast MRI for differentiation of subcortical structures for DBS targeting: the Fast Gray Matter Acquisition T1 Inversion Recovery (FGATIR). Neuroimage, 47(2), 44-52.
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Tournier, J.-D. (2019). MRtrix3: A fast, flexible and open software framework for medical image processing and visualisation. NeuroImage, 202, 116-137.