Multimodal 7T Imaging of Thalamic Nuclei for Preclinical Deep Brain Stimulation Applications

Abstract

Precise neurosurgical targeting of electrode arrays within the brain is essential to the successful treatment of a range of brain disorders with deep brain stimulation (DBS) therapy. Here, we describe a set of computational tools to generate in vivo, subject-specific atlases of individual thalamic nuclei thus improving the ability to visualize thalamic targets for preclinical DBS applications on a subject-specific basis. A sequential nonlinear atlas warping technique and a Bayesian estimation technique for probabilistic crossing fiber tractography were applied to high field (7T) susceptibility-weighted and diffusion-weighted imaging, respectively, in seven rhesus macaques. Image contrast, including contrast within thalamus from the susceptibility-weighted images, informed the atlas warping process and guided the seed point placement for fiber tractography. The susceptibility-weighted imaging resulted in relative hyperintensity of the intralaminar nuclei and relative hypointensity in the medial dorsal nucleus, pulvinar, and the medial/ventral border of the ventral posterior nuclei, providing context to demarcate borders of the ventral nuclei of thalamus, which are often targeted for DBS applications. Additionally, ascending fiber tractography of the medial lemniscus, superior cerebellar peduncle, and pallidofugal pathways into thalamus provided structural demarcation of the ventral nuclei of thalamus. The thalamic substructure boundaries were validated through in vivo electrophysiological recordings and post-mortem blockface tissue sectioning. Together, these imaging tools for visualizing and segmenting thalamus have the potential to improve the neurosurgical targeting of DBS implants and enhance the selection of stimulation settings through more accurate computational models of DBS.

3T MRI Whole-Brain Microscopy Discrimination of Subcortical Anatomy, Part 2: Basal Forebrain

“…45 We have used an asterisk to denote the ZI to visually emphasize that this structure is better defined by bordering structures and changes in shape at different points along the neuroaxis. The superior portion of the ZI appears as a thin hyperintense band on the TSE sequence superomedial to the inferior portion of the genu of the internal capsule (79), superior to the lenticular fasciculus (58), inferior to the thalamic fasciculus (27) (Figs 3 and 5B), and anterolateral to (Table 2) in the inferior portion of the zona incerta (asterisk), which corresponds with a better therapeutic profile according to Plaha et al 22 FIG 4. Selected images illustrating the hippocampal-thalamic pathways.…”

“…48,49 This structure appears continuous with the anterior inferior thalamic peduncle, appearing as a sheet-like vertically oriented structure lateral to the postcommissural fornix, anterosuperior to the ansa lenticularis, posteroinferior to the anterior commissure, and su- Selected images illustrating the pallidothalamic tracts. Sagittal, oblique axial (the dashed line in A represents the oblique imaging plane for B), and coronal images illustrating the complex 3D shapes and spatial relationships of the ansa lenticularis (5), lenticular fasciculus (58), and thalamic fasciculus (27). B, The ansa lenticularis originates from the inferomedial globus pallidus internus (17) and joins the lenticular fasciculus (H2 field of Forel) in the very hypointense prerubral H Fields of Forel (78).…”

Improved susceptibility‐weighted imaging for high contrast and resolution thalamic nuclei mapping at 7T

“…It is currently unknown whether modifications of the SWI phase‐magnitude combination, in particular, could enhance its ability to image non‐venous tissues such as the thalamus. Previous reports have found promising results for thalamic mapping using the conventional, venography‐oriented SWI contrast, but to our knowledge none have proposed or explored potential dedicated improvements . A main reason for this shortcoming could be the fact that, to our knowledge, the SWI combination parameters are typically fixed and cannot be modified by users directly on the console (“online”), requiring dedicated expertise in MRI data reconstruction to explore such modifications.…”

Noncontrast‐enhanced time‐resolved 4D dynamic intracranial MR angiography at 7T: A feasibility study

“…Recently, technical advances in both hardware and software of high‐field MRI has enabled 7T MRI systems to become commercially available for human study. A number of MRI techniques, 3D anatomical and angiographic sequences in particular, have been developed and optimized at 7T to enable high‐resolution acquisition by making use of the increased signal‐to‐noise ratio (SNR) at ultrahigh‐field . ASL theoretically benefits from ultrahigh‐field with the dual benefits of increased SNR and prolonged longitudinal relaxation times .…”

“…A number of MRI techniques, 3D anatomical and angiographic sequences in particular, have been developed and optimized at 7T to enable high-resolution acquisition by making use of the increased signal-to-noise ratio (SNR) at ultrahighfield. [17][18][19][20][21] ASL theoretically benefits from ultrahigh-field with the dual benefits of increased SNR and prolonged longitudinal relaxation times. 22 A prolonged bolus of the labeled blood is expected in NCE 4D MRA at 7T.…”