Abstract
Structural brain imaging provides a critical framework for performing stereotactic and intraoperative MRI-guided surgical procedures, with procedural efficacy often dependent upon visualization of the target with which to operate. Here, we describe tools for in vivo, subject-specific visualization and demarcation of regions within the brainstem. High-field 7T susceptibility-weighted imaging and diffusion-weighted imaging of the brain were collected using a customized head coil from eight rhesus macaques. Fiber tracts including the superior cerebellar peduncle, medial lemniscus, and lateral lemniscus were identified using high-resolution probabilistic diffusion tractography, which resulted in three-dimensional fiber tract reconstructions that were comparable to those extracted from sequential application of a two-dimensional nonlinear brain atlas warping algorithm. In the susceptibility-weighted imaging, white matter tracts within the brainstem were also identified as hypointense regions, and the degree of hypointensity was age-dependent. This combination of imaging modalities also enabled identifying the location and extent of several brainstem nuclei, including the periaqueductal gray, pedunculopontine nucleus, and inferior colliculus. These clinically-relevant high-field imaging approaches have potential to enable more accurate and comprehensive subject-specific visualization of the brainstem and to ultimately improve patient-specific neurosurgical targeting procedures, including deep brain stimulation lead implantation.
Highlights
Structural brain imaging has become an important tool for guiding neurosurgical procedures, including microelectrode mapping, catheter insertion, ablation, and deep brain stimulation (DBS) lead implantation [1, 2]
In four subjects (8 hemispheres), structural susceptibility-weighted imaging (SWI) scans and warped slices were used as a guide to define seed points and waypoints for probabilistic tractography analysis of the superior cerebellar peduncle (SCP), medial lemniscus (ML), and lateral lemniscus (LL) (Fig 3)
The reconstruction overlap within the brainstem between tractography and nonlinear atlas warping, was 45±4% for SCP, 45±24% for ML, and 39±13% for LL, which reflected consistent albeit slight misalignments in which tract borders identified through the nonlinear warping approach were rendered slightly caudal to the diffusion tractography volume reconstructions
Summary
Structural brain imaging has become an important tool for guiding neurosurgical procedures, including microelectrode mapping, catheter insertion, ablation, and deep brain stimulation (DBS) lead implantation [1, 2]. Other studies utilizing very high resolution ex vivo imaging and histology have been able to identify regions within the human brainstem [37] and validate tractography [38]. The acquired dataset enabled: 1) investigating what contrast exists in the non-human primate brainstem using high-field 7T susceptibility-weighted imaging, 2) developing methods to identify structures not directly visible even with high-field MRI, 3) generating probabilistic fiber tractography of the brainstem, 4) assessing the anatomical variability of brainstem structures across eight rhesus macaques, and 5) comparing the nuclei and fiber tract reconstructions to post-mortem histology. Improvements in the visualization of anatomical targets using these tools hold promise for more accurate subject-specific surgical targeting of interventions in the brainstem [9] influencing the clinical outcomes of neurosurgical interventions in this region of the brain
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