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James Stewart's Research

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Computer Assisted Mosaic Arthroplasty (CAMA)

Mosaic arthroplasty is a surgical procedure to repair a cartilage defect. Small plugs of cartilage and bone are transplanted into the defect from a non-load-bearing part of the joint.

The procedure is technically demanding, requiring that (a) the original cartilage surface be determined, (b) a set of plugs be found to reconstruct that surface, and (c) the plugs be harvested and placed very accurately.

Conventional mosaic arthroplasty is done manually and has variable results. Our research provides better surgical outcomes through computer planning and computer guidance.

Arthroscopic CAMA

We performed the first arthroscopic CAMA on the human knee.
Template-Guided CAMA

We performed the first template-guided CAMA on the human knee.
presentation

Study Comparing CAMA to Conventional Mosaic Arthroplasty

An animal study showed that computer-assisted methods outperform the conventional method in mosaic arthroplasty.
paper

Predication of the Cartilage Surface

A comparison of three methods of predicting the original cartilage surface over a defect found that a cubic spline gave the best results.
poster

Automatic Planning of Surgery

A computer program was developed to automatically plan the pattern of plugs over a defect, and to determine where those plugs should be harvested to produce the best repair surface.

CAMA Publications

M. Kunz, S. Waldman, J. Rudan, D. Bardana, J. Stewart, "Computer Assisted Mosaic Arthroplasty Using Patient-Specific Instrument Guides", Knee Surgery, Sports Traumatology, Arthroscopy, to appear
J. Inoue, M. Kunz, M. Hurtig, S. Waldman, J. Stewart, "Automated Planning of Computer Assisted Mosaic Arthroplasty", Medical Image Computing and Computer Assisted Intervention (MICCAI), pp 265-272, 2011.
D. Onceanu and J. Stewart, "Direct Surgeon Control of the Computer in the Operating Room", Medical Image Computing and Computer Assisted Intervention (MICCAI), pp 121-128, 2011.
J. Li, D. Bardana, J. Stewart, "Augmented Virtuality for Arthroscopic Knee Surgery", Medical Image Computing and Computer Assisted Intervention (MICCAI), pp 185-192, 2011.
M. Kunz, M. Hurtig, S. Waldman, S. Devlin, J. Rudan, D. Bardana, J. Stewart, "Image-guided surgical techniques for cartilage repair - an animal trial", World Congress of the International Cartilage Repair Society (ICRS), p 190, podium presentation, 2010.
J. Inoue, M. Kunz, S. Waldman, M. Hurtig, J. Stewart, "Automated planning of computer-guided mosaic arthroplasty", World Congress of the International Cartilage Repair Society (ICRS), p 220, 2010.
M. Kunz, S. Devlin, R.H. Gong, J. Inoue, S. Waldman, M. Hurtig, P. Abolmaesumi, J. Stewart, "Prediction of the Repair Surface over Cartilage Defects: A Comparison of Three Methods in a Sheep Model", Medical Image Computing and Computer Assisted Intervention (MICCAI), pp 75-82, 2009.
M. Kunz, S. Devlin, M. Hurtig, S. Waldman, J. Stewart, "Comparison of two CT-based intraoperative navigation systems for moasic arthroplasty", International Society for Computer Assisted Orthopaedic Surgery, pp 43-46, 2009.
M. Kunz, S. Devlin, J.F. Rudan, S.D. Waldman, J. Stewart, M. Hurtig, "Computer-assisted planning for mosaic arthroplasty", Computer Assisted Radiology and Surgery, S102-S103, 2009.
M. Hurtig, M. Kunz, S. Devlin, J. Rudan, J. Stewart, D. Bardana, S. Waldman, "Individualized rapid prototyped guides for optimization of mosaic arthroplasty", International Cartilage Repair Society, Vol 8, page 265, 2009.
K. Kassil, J. Stewart, "Evaluation of a Tool-Mounted Guidance Display for Computer-Assisted Surgery", ACM International Conference on Human Factors in Computing Systems (CHI), pp 1275-1278, 2009.
A. Bell, J. Matyas, M. Hurtig, "Advantages of CT arthrography using anionic contrast agents for functional imaging of cartilage", Transactions Orthopaedic Research Society, v34, page 1156, 2009.
M. Kunz, J. Rudan, D. Bardana, J. Stewart, S. Waldman, R. Ellis, "Computer-Assisted Mosaicplasty", Computer Assisted Orthopaedic Surgery, pp 358-360, 2008.

Surgical User Interfaces

Direct Surgeon Control of the Computer

We developed a magnetic, joystick-like device that allows the surgeon to directly control the computer using a tracked surgical probe, a common tool in the operating room.
3D Guidance for Arthroscopic Knee Surgery

Our arthroscopic guidance system shows a real-time 3D view of the interior of the joint and projects the arthroscope image onto the bone. We found that the 3D view improved targets acquisition in novice residents.
Tool-Mounted Guidance Display

With our tool-mounted guidance display, surgeons do not have to look away from the patient when sawing or drilling under computer guidance.

Uncertainty Visualization

Uncertainty Visualization for Pedicle Screw Insertion

Uncertainty is present in all surgical computer guidance systems, but is rarely shown in a meaningful way. We developed several methods of providing uncertainty information on the guidance display. For the delicate task of inserting screws into the spine, we showed that surgeons were able to correctly interpret the uncertainty information and that the extra uncertainty information on the guidance display did not adversely affect surgical performance.
Uncertainty Visualization for Osteoid Osteoma Excision

A study of the simulated excision of an osteoid osteoma showed that the presence of uncertainty information improved some measures of surgical performance.

Volume Visualization

Vicinity Shading

A shading model for volumetric data is described that enhances the perception of surfaces within the volume. The model incorporates uniform diffuse illumination, which arrives equally from all directions at each surface point in the volume
Depth Perception in Volumes

We found that stereopsis and simulated aerial perspective could improve depth perception in CT volumes. Surgeons make use of CTs in planning and performing operations, so an improvement of depth perception in CT volume rendering may help diagnosis and surgical planning.
Accelerated Volume Rendering

An new volume rendering algorithm efficiently exploits empty regions in the data set to speed up rendering.

Cartographic Visualization

Illuminated Choropleth Maps

A choropleth map shows a data distribution on a map using differently coloured classes for different ranges of the data. We show that soft shadows can be added to show differences within a class.
Shading of LIDAR Terrains

We show that a "cloudy day" illumination model can provide better 3D perception of 2D LIDAR images, such as a city image acquired from a satellite.

Meshing for Computer Modelling

Hierarchical Hexagonal Meshes

Hierarchical hexagon meshes have several advantages over the standard "latitude/longitude" mesh when modelling the Earth's surface. We developed an algorithm to triangulate a hierarchical hexagon mesh so that it can be rendered on the computer screen.
details, results, paper

Tunneling for Triangle Strips

A method to build and maintain a good set of triangle strips in both static and continuous level-of-detail (CLOD) meshes. Update: A new tunneling algorithm has been developed which performs much better than the one described above (see "results" link above).

Computer Graphics

paper

Automatic Scene Composition

A constraint based automatic placement system, which allows the user to quickly and easily lay out complex scenes using constraints, pseudo physics, and a semantic database.
details

Terrain Rendering

An efficient algorithm for the computation of the horizon at every point on a terrain. The horizon is used for occlusion culling and for realistic shading.
details, results, paper

Cloth Shading

An algorithm to shade irregular surfaces, such as cloth by computing, for each point on the surface, how much of the outside environment is visible.
paper

Approximate Visibility

A robust, hardware-accelerated algorithm to compute an approximate visibility map, which describes the visible scene from a particular viewpoint. This has application to discontinuity meshing.
details, paper

Shadows and Discontinuity Meshing

A fast, practical algorithm to compute the shadow boundaries in a polyhedral scene illuminated by a polygonal light source.
details, paper

Shape-From-Shading under Diffuse Lighting

An algorithm to compute shape-from-shading under diffuse illumination using an approximate surface radiance model which incorporates shadows, interreflections, and surface orientation.
paper

Incremental Visiblity

An algorithm to maintain the sequence of lines visible from a moving viewpoint in the plane. The algorithm usedes space linear in the number of visual discontinuity lines.