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Surgical simulation has many applications in medical education, surgical training, surgical planning, and intra-operative assistance. However, extending current surface-based computer graphics methods to model phenomena such as the deformation, cutting, tearing, or repairing of soft tissues poses significant challenges for real-time interactions. This paper discusses the use of volumetric methods for modeling complex anatomy and tissue interactions. New techniques are introduced that use volumetric methods for modeling soft tissue deformation and tissue cutting at interactive rates. An initial prototype for simulating arthroscopic knee surgery is described which uses volumetric models of the knee derived from 3D Magnetic Resonance Imaging, visual feedback via real-time volume and polygon rendering, and haptic feedback provided by a force feedback device. To be published in Journal of Medical Image Analysis, December, 1997.This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy i n whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories of Cambridge, Massachusetts; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories. All rights reserved. Copyright © Mitsubishi Electric Information AbstractSurgical simulation has many applications in medical education, surgical training, surgical planning, and intra-operative assistance. However, extending current surfacebased computer graphics methods to model phenomena such as the deformation, cutting, tearing, or repairing of soft tissues poses significant challenges for real-time interactions. This paper discusses the use of volumetric methods for modeling complex anatomy and tissue interactions. New techniques are introduced that use volumetric methods for modeling soft tissue deformation and tissue cutting at interactive rates. An initial prototype for simulating arthroscopic knee surgery is described which uses volumetric models of the knee derived from 3D Magnetic Resonance Imaging, visual feedback via real-time volume and polygon rendering, and haptic feedback provided by a force feedback device.

We report grammar inference experiments on partially parsed sentences taken from the Wall Street Journal corpus using the inside-outside algorithm for stochastic context-free grammars. The initial grammar for the inference process makes no ,assumption of the kinds of structures and their distributions. The inferred grammar is evaluated by its predicting power and by comparing the bracketing of held out sentences imposed by the inferred grammar with the partial bracketings of these sentences given in the corpus. Using part-of-speech tags as the only source of lexical information, high bracketing accuracy is achieved even with a small subset of the available training material (1045 sentences): 94.4% for test sentences shorter than 10 words and 90.2% for sentences shorter than 15 words.

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