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Brain mapping in stereotactic surgery: A brief overview from the probabilistic targeting to the patient-based anatomic mapping

CHU Clermont-Ferrand, Hôpital Gabriel Montpied, Service de Neurochirurgie A, Clermont-Ferrand, F-63003, France.
NeuroImage (Impact Factor: 6.36). 02/2007; 37 Suppl 1:S109-15. DOI: 10.1016/j.neuroimage.2007.05.055
Source: PubMed

ABSTRACT

In this article, we briefly review the concept of brain mapping in stereotactic surgery taking into account recent advances in stereotactic imaging. The gold standard continues to rely on probabilistic and indirect targeting, relative to a stereotactic reference, i.e., mostly the anterior (AC) and the posterior (PC) commissures. The theoretical position of a target defined on an atlas is transposed into the stereotactic space of a patient's brain; final positioning depends on electrophysiological analysis. The method is also used to analyze final electrode or lesion position for a patient or group of patients, by projection on an atlas. Limitations are precision of definition of the AC-PC line, probabilistic location and reliability of the electrophysiological guidance. Advances in MR imaging, as from 1.5-T machines, make stereotactic references no longer mandatory and allow an anatomic mapping based on an individual patient's brain. Direct targeting is enabled by high-quality images, an advanced anatomic knowledge and dedicated surgical software. Labeling associated with manual segmentation can help for the position analysis along non-conventional, interpolated planes. Analysis of final electrode or lesion position, for a patient or group of patients, could benefit from the concept of membership, the attribution of a weighted membership degree to a contact or a structure according to its level of involvement. In the future, more powerful MRI machines, diffusion tensor imaging, tractography and computational modeling will further the understanding of anatomy and deep brain stimulation effects.

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    • "The 10 centres of stimulating contacts (pooling left plus right hemispheres) were projected into the 2D-slice Schaltenbrand and Bailey atlas (1959) and into a 3D-voxel MRI-based 4.7 tesla (T) atlas (Lemaire et al., 2007a, b) of the diencephalon–mesencephalic junction. To identify structures potentially involved in the therapeutic effect, we hypothesized that the volume of tissue excited by the current around the electrode contact should not extend laterally more than 3 mm. "

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    • "The improved signal-to-noise ratio (SNR) and the possibility to benefit from spontaneous contrasts between white and gray matter signals can aid the identification of subtle structural features, with good geometric resolution. Based on our experience on MRI anatomic mapping [15] [16] [19] [20], we have introduced a modification to the previously described Cortex Attenuated Inversion Recovery sequence [17], named White matter Attenuated Inversion Recovery (WAIR). We found that images generated by this sequence result in a consistent delineation of the ventral group of thalamic nuclei and the fiber projections reaching them from the basal ganglia as well as the cerebellar and lemniscal pathways. "
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    ABSTRACT: The ventrointermediate nucleus (Vim) of the thalamus is still considered "invisible" on current magnetic resonance imaging (MRI), requiring indirect methods based on stereotactic atlases for estimation of its location. Direct visualization of Vim is desirable to improve targeting. To evaluate the ability of Inversion-Recovery 1.5-T MR images to produce high-resolution, anatomical depiction of the thalamus suitable for direct Vim targeting. Twenty patients with essential tremor or tremor associated with Parkinson's disease received Vim deep brain stimulation (DBS). Fahn-Tolosa-Marin and Unified Parkinson's Disease Rating Scale (UPDRS) tremor scores were assessed pre- and postoperatively. Preoperative stereotactic 1.5-T MR images of the thalamus were acquired using a White Matter Attenuated Inversion Recovery (WAIR) sequence. Thalamic nuclei were manually contoured on the basis of spontaneous MRI contrasts; labeling relied on 3D identification from stereotactic books and in-house ex vivo 4.7-T microscopic MRI atlas. Vim was then directly probed for electrophysiological confirmation and determination of the optimal site for electrode placement. The shape, spatial orientation, and signal contrast of Vim as depicted on our WAIR images were similar to those observed on the Schaltenbrand and Bailey atlas, as well as in our high-field MRI atlas. These images were successfully used for pure direct Vim targeting: at the last follow-up (median = 46.3 months), the average tremor score improved from 3.80 preoperatively to 0.50 postoperatively (on stimulation; P < 0.01). 1.5-T MRI with WAIR sequence provides high-quality images of Vim suitable in DBS surgery, for accurate preoperative planning, direct targeting and anatomic analysis.
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