Biomechanics for Computer Assisted Medical Interventions

At the crossroads of medicine, IT and bioengineering, computer-assisted medical and surgical procedures (CAMS) are booming, in response to strong medical demand. In parallel with the effective introduction of IT into hospitals (medical imaging, integrated hospital information systems), medical procedures are becoming less and less "invasive", to reduce patient trauma, hospitalization times and post-operative consequences. Against this backdrop, GMCAO has emerged to support clinical procedures by combining medical imaging, modeling, data fusion and robotics techniques. In order to be increasingly precise, surgical strategies will, for example, combine traditional preoperative planning with simulation techniques based on complex models (statistical or biomechanical models, for example). Similarly, as surgical gestures become less and less invasive, with reduced vision and restricted access to organs, virtual reality techniques may be used to enhance the surgeon's perception, and robotic guidance systems may be required to complement his or her dexterity.

GMCAO methodologies are often presented in three chronological stages. In the first stage, data are collected (traditional medical imaging, computer vision, metrology) and then injected into a priori knowledge (anatomical models, statistical models, etc.) in order to build a virtual model of the patient. The second stage involves planning the medical or surgical intervention. The surgeon will use the virtual patient model to define the optimal surgical strategy. This strategy may involve optimization tools (to deliver the optimum radiation dose to pathological tissues in radiotherapy, for example), or geometric and/or mechanical modeling tools (for difficult approaches with complex trajectories, or in situations where the anatomical structures being operated on may move or even deform during the operation). Finally, the last stage of GMCAO methodologies involves transferring the planning defined on the patient model to operating room conditions. In other words, the computerized world of data, images and preoperative planning is linked to the real world of the operating room, with the patient, the surgeon and his or her ancillaries. Medical robotics and its computerized ancillaries are the answer that has been proposed to surgeons to materialize this link between computerized planning and the operating room.

The aim of this article is to provide an overview of the tissue biomechanics techniques used in a virtual model of the patient. By tissue biomechanics, we mean the use of modeling tools to predict the deformations of living soft tissues. We will be looking at both biomechanical models used to assist surgical planning (i.e. prior to surgery) and models used in real time (i.e. during surgery or for immediate feedback...