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Multidimensional tomographic image processing can be used to provide the surgeon useful information on volume, size, shape, location and anatomical relationships of intracranial lesions. Using a reference system this information can be used to "simulate" and interactively optimize different treatment modalities such as surgery, radiation therapy, photodynamic therapy, hyperthermia, etc. Finally, this computer generated data can be transposed accurately on the "real" physical world or can be used to drive instruments such as microscopes, lasers, etc., leading to automation of neurosurgical procedures. Computer reconstruction of image data (CT, MRI, DA) acquired under stereotactic conditions allows three—dimensional and multiplanar representation of a target volume and surrounding anatomy. Target vOlume definition is the common step of any "volume"—dependent procedure, including diagnostic histological mapping, resection or internal decompression of lesions, radiation, hyperthermia, photodynamic therapy, etc. (6, 8, 13, 19, 28,31, 34, 36). An image—based surgical treatment planning system has been developed to provide an interactive "real time" three-dimensional and multiplanar stereotactic neurosurgical planning that allows target volume definition, rotation, reconstruction in arbitrary planes, selection of surgical trajectory and optimization of surgical approach (36, 37). Real time computation allows surgical target and trajectories to be selected, displayed, and optimized in 3D and 2D multiplanar views; at the same time this preplanning can be "mathematically" transposed into intraoperative stereotactic space, and therapy can be directed to this volumetric information. Diagnostic and therapeutic stereotactic procedures can be accomplished accurately using these image-generated data to guide endoscopes, microscopes, lasers or other surgical instruments. Image-based stereotactic preplanning is the first step in automated surgical procedures (36, 37); these computerized data can also he used to deliver highly focused energy from specific components of the electromagnetic spectrum (gamma radiation, visible light, microwaves, etc.) or derived from heavily charged particles (protons, etc.). The common factor in these procedures is accurate target volume definition and space localization. This short-course notes describe our current hardware and software configuration currently used in our institution to support image "guided" or "directed" neurosurgical stereotactic procedures. The final goal is optimization of neurosurgical procedures for intracranial lesions. Performance of image-guided stereotactic neurosurgical procedures can be divided into four successive steps: 1. Stereotactic Image Data Acquisition 2. Computerized Pornographic Image Processing for Planning 3. Transposition of "Simulated" Planning into Physical World 4. Diagnostic or Therapeutic Neurosurgical Procedure
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