Preoperative Diffuson Tensor Imaging (DTI): contribution to surgical planning and validation by intraoperative electrost
Surgical resection of tumors located within the so-called eloquent areas requires the pre- and intraoperative identification of cortical and subcortical functional sites to achieve the goal of a satisfactory tumor resection associated with a full preserva
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Introduction Surgical resection of tumors located within the so-called eloquent areas requires the pre- and intraoperative identification of cortical and subcortical functional sites to achieve the goal of a satisfactory tumor resection associated with a full preservation of the patient’s integrity. Diffusion tensor imaging (DTI) and fiber tractography (FT) are magnetic resonance techniques based on the concept of anisotropic water diffusion in myelinated fibers, which enable three-dimensional reconstruction and visualization of white-matter tracts. Threedimensional visualization of the functional fibers and their relationship with brain lesions is helpful for preoperative evaluation and intraoperative navigation, combining DTI information with those of direct electrical stimulation (DES). In this chapter, we will describe the contribution of DTI-FT to surgical planning and, when combined with DES, to safety in the performance of surgical removal of tumors involving functional brain areas.
DTI data acquisition and FT processing DTI is an innovative magnetic resonance imaging (MRI) technique, introduced in the mid 1990s [37, 38], that allows to assess the axonal H. Duffau (ed.), Brain Mapping © Springer-Verlag/Wien 2011
organization of the brain, using the anisotropic water diffusion. DTI uses the translational motion of water molecules to obtain anatomic information [1]. Water molecules are supposed to move more easily along the axonal bundles rather than perpendicular to these bundles because there are fewer obstacles to prevent movement along the fibers. By the characterization of the anisotropic diffusion of water, an entirely new image contrast is provided which is based on structural orientation [2, 12, 16]. To identify the course of white matter tracts, DTI tractography methods require the delineation of regions of interest (ROIs) as starting seed points for tracking [25]. ROIs can be delinated automatically or manually. Manual delineation of ROIs requires a priori anatomical knowledge and it is very helpful when the anatomy is distorted such as in the case of tumors. In our institute we use the method described by Catani and Thiebaut de Schotten [13]: a ROIs is defined around areas of white matter that represent “obligatory passages” along the course of each tract. If the ROI representing an obligatory passage contains only fibers of the tract of interest, a single ROI approach is used. A one-ROI approach is used for the arcuate fasciculus, cingulum, corpus callosum, anterior commissure, and fornix. When a tract shares its obligatory passages with one or more other tracts, a two-ROI approach is used. The second ROI is defined such that it contains
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L. Bello, A. Castellano, E. Fava, G. Casaceli, M. Riva, A. Falini
at least a section of the desired fasciculus but does not contain any fibers of the undesired fasciculi that pass through the first ROI. The two-ROI approach is used for the corticospinal tract and the uncinate, inferior longitudinal, and inferior fronto-occipito fasciculi. A second ROI can
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