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Biomedical subjects

S Lavallee

Publications and source records attributed to S Lavallee.

5 recordsLinked to original sources
PubMed1998

Automated 3-dimensional computed tomographic and fluoroscopic image registration.

The registration of 3-dimensional (3-D) anatomical surfaces to sensor data such as intraoperative fluoroscopy is one of the basic problems in computer integrated surgery. The main objective is to find the relationship between 3-D preoperative computed tomographic images and a pair of intraoperative fluoroscopic images. Consequently, surgical navigation devices can use this relationship to provide improved surgical guidance. The proposed registration strategy presents a noninvasive anatomy-based (frameless) method for registration. In this article, we propose a cooperative approach between registration and contour segmentation on fluoroscopy. This approach is based on the duality between registration and segmentation in a model-based vision system. It associates a likelihood value to each pixel that corresponds to the probability that the pixel belongs to the contour of the object of interest. The registration is then achieved between backprojection lines stemming from likely contour pixels and the 3-D surface model of the object of interest. Then, in order to take into account the internal contour points extracted by the cooperative approach, we propose a new line to surface distance computation algorithm to be used during the data to model distance minimization step. Finally, we present the obtained results that demonstrate the validity of the proposed approach in carrying out accurate 3-D and 2-D registration.

Algorithms↗
PubMed1998

Fiber-based anterior cruciate ligament model for biomechanical simulations.

Although accurate predictions of the behavior and function of the anterior cruciate ligament would aid in diagnosis and operative treatment, no agreement exists on the best way to model the ligament with a reliable description of its mechanical and geometric features. We propose a new model of the anterior cruciate ligament based on multiple viscoelastic curvilinear fibers. This model was used for quasi-static simulations of the passive motion of eight porcine knees, after registration of the passive trajectories and digitization of the surface of the ligament in flexion. Simulations of anterior cruciate ligament deformations during passive motion predicted a fiber strain of less than 20%, low insertion forces, and isometric anterior fibers. The model explains actions of the ligament fibers, as reported in the literature, better than classic models based on linear fibers and consistent with the mechanical properties of the anterior cruciate ligament.

Animals↗
PubMed1997

Computer assisted spine surgery.

When inserting screws into a vertebral pedicle, the surgeon usually exposes the back part of the vertebra and uses his or her anatomic knowledge to align the drill in the proper direction. A slight error in direction may result in an important error in the position of the tip of the screw. This is done with no direct visibility of crucial structures (spinal cord, pleura, vessels). Statistical analysis of a series of surgical procedures has shown that 10% to 40% of the screws are not installed correctly. To reduce the risk of complication, a computer assisted method is proposed that enables the surgeon to place a screw at a position preoperatively defined in 3 dimensions using computed tomography images. This allows the surgeon to align a standard surgical drill with the optimal position and direction. The depth of the pilot hole during drilling also is monitored by the system to prevent penetration of the anterior cortex of the vertebral body. Using this procedure, in vitro tests were performed and showed that an accuracy of less than 1 mm can be obtained. Clinical trials were done in 10 patients who suffered severe scoliosis or spondylolisthesis. The trajectory of the holes drilled in L2, L3, L4, and L5 vertebrae were checked for all clinical tests. Postoperative radiographs and computed tomography scans showed that the screws were well inserted in each plane for each pedicle. This technique also can be used to perform osteosynthesis at the thoracic and cervical levels.

Adult↗
PubMed1992

Potential use of robots in endoscopic neurosurgery.

A 6-axis stereotactic robot has been designed and linked to a stereotactic frame for routine use. Robot software allows the positioning of a probe holder in order to reach a given target. A calibration step enables the robot to compute the position of the x-ray beam and correct its final position to avoid parallax errors. The co-ordinates of the target are presently taken from anteroposterior and lateral X-rays using a digitizing table. Connection with a digitized angiography system is in progress and will allow direct sampling of numerical data from the x-ray data. Further steps will include connections with a 3D-reconstructed image from MRI and CAT as well as with a resident computerized atlas. Present experience after 14 months of daily practice represents 140 stereotactic procedures which can be extended to any special use, including endoscopic approaches.

Brain Diseases↗