871 research outputs found
Medical Visualization and Simulation for Customizable Surgical Guides
No full textThis thesis revolves around the development of medical visualization tools for the planning of CSG-based surgery. To this end, we performed an extensive computerassisted surgery (CAS) literature study, developed a novel optimization technique for customizable surgical guides (CSG), and introduce three visualization techniques to make the planning more realistic and allow for remote visualization. In Chapter 2 we document the results of an extensive overview study, in which the use of visualization in CAS is analysed. We collected a comprehensive database of visualization relevant CAS publications, and analyse the visualization techniques that are used. We also classify important CAS-related surgical tasks and explain how and why visualization is used. Further, we analysed how surgical plans are transferred to the operating theater. Finally, we discuss how visualization is used in the four most prominent application areas of CAS. Based on this review, we were able to pinpoint interesting new research directions. One of these is the apparent lack of proper tools for CSG-based surgery, a challenge that we addressed in Chapter 3. The optimization of CSG parameters such that the CSG can be docked on bone in an accurate and stable way, is important in the planning of CSG-based surgery. The adjustable nature of the CSG, which allows it to become patient-specific, unfortunately also makes it inherently unstable. Optimizing the configuration by hand leads to poor results as we demonstrated with experiments. In Chapter 3, we therefore solve the problem in sillico. We described a novel planning tool that is able to automatically optimize a CSG for an arbitrary patient. We established this by combining a physical simulator, which models the physical interaction between the CSG and the bone, with a genetic optimization process. With experiments, we were able to prove that our optimization tool produces CSG configurations that lead to accurate and stable docking. In Chapter 4, we address the challenge of enhancing the planning environment with appropriate visualization techniques that help to understand how a CSG is connected to the bone. The state-of-the-art rendering tools in CAS applications are not able to accurately and effectively communicate how the CSG attaches to the bone. However, ambient occlusion (AO) is an illumination technique that is particularly effective at depicting contact between objects, but is generally computationally expensive. Therefore, we developed an efficient version of this algorithm such, that it can be used in the planning pipeline to effectively depict CSG-bone contact. We took the visualization one step further by introducing photo-realistic and physically based volume rendering. Chapter 5 describes Exposure Render, a complete volume rendering framework based on stochastic raytracing, and is able to incorporate a host of otherwise difficult to obtain photorealistic camera, light, and material effects. It is a well known fact that these help to understand shape, depth and size. Therefore, we employed Exposure Render to build a prototype doctor-patient communication system. With this remote visualization system, a doctor can counsel a patient from a distance, or a patient can perform self health management by uploading their tomographic data. In Chapter 6 we optimize the performance of Exposure Render. We introduce visibility sweeps, an efficient method to compute and store visibility information in volume data sets. With this method, it becomes possible to efficiently query approximate global visibility information in a volume data set. We demonstrate that this visibility information can be harnessed to improve the efficiency of the ray sampling processes in Exposure Render, which results in faster convergence. Though we demonstrate the effectiveness of visibility sweeps in the context of stochastic volume rendering, its use stretches beyond this application. Many areas of medical visualization and CAS rely on visibility information, such as automatic view finding in volume data and in various areas of CAS e.g., access, resection and implant planning. In our project it is also relevant because the visibility information can be used to make the physical simulator more realistic, for instance by avoiding docking trajectories that are associated with high risk of tissue damage. The research described in this thesis was part of the project Novel pre-operative planning and intraoperative guidance system for shoulder replacement surgery (10812), funded by the Dutch Technology Foundation.Intelligent SystemsElectrical Engineering, Mathematics and Computer Scienc
Letter from E.R. Fryer, Regional Director, War Relocation Authority, to Mrs. George Nakamura, September 8, 1942
No full textCorrespondence from E.R. Fryer to Dorothy Nakamura regarding Nakamura's request for her family to return to their home in Military Area No. 1 due to their status as a mixed-marriage family.The Japanese American Archival Collection documents the people, places, and daily life of Japanese Americans, primarily those who lived in the once thriving community of pre-war Florin in the Sacramento region, as well as the conditions in American incarceration camps during World War II. The approximately 7,000 original items include personal and official letters, photographs, diaries, arts and crafts, newsletters, textiles, camps artifacts, yearbooks and other publications
Structural and mechanical characterization of the peri-prosthetic fibrous membrane
No full textIn this pilot study, we obtained the peri-prosthetic fibrous membrane of eleven patients undergoing hip revision surgery due to aseptic loosening. We investigated the molecular content of the tissue by real-time PCR (RT-PCR) and the structural properties by histology and confocal microscopy. Atomic force microscopy (AFM) and nanoindentation were used to determine the mechanical properties of the peri-prosthetic tissue, respectively at the nano- and microscopic scale. Finally, the AFM data was evaluated using the statistical finite mixture models theory, to link the contributions of different constituents of this heterogeneous tissue to the measured mechanical propertiesBMEBioMechanical EngineeringMechanical, Maritime and Materials Engineerin
Inherently safe water jet dissector
No full textAseptic loosening is the major failure mode for hip prostheses. Currently, loosened prostheses are revised during open surgery. Because of a high complication rate, this demanding procedure cannot be performed in patients with a poor general health. We are developing an alternative minimally invasive refixation procedure that leaves the prostheses in place, but relies on removing the interface membrane and replacing it with bone cement. This thesis describes the design considerations and challenges for a water jet dissector for removal of the interface membrane in a minimally invasive hip refixation surgery.BMEBiomechanical EngineeringMechanical, Maritime and Materials Engineerin
Modelling Micromotion of Implants in the Rat Femur: A rat femoral knee prosthesis to simulate aseptic loosening
No full textBackground: Aseptic loosening [AL] of cementless implants is causing approximately 60% of total knee and total hip arthroplasty revisions. AL is caused among other factors by micromotion. The result is that the bone around the prosthesis is replaced by a fibrous membrane. This fibrous membrane allows for more micromotion and we thus enter a vicious circle of loosening. In-vivo research for treatments of AL and research into preventing AL is rare. When in vivo research is conducted, this is commonly done in large animals such as sheep and dogs. To bring down costs and increase reproducibility it is desired to recreate the fibrous membrane in a smaller animal. Therefore, an unstable knee hemiprosthesis was designed for the femur of the Wistar rat. Methods: First a test was conducted on cadaverous adult male Wistar rat femurs to assess whether it was easier to access the medullary canal of the femur from the hip or the knee side. Then, a second test was conducted on cadaverous rat femurs (n=8) to assess the depth and width to which we could implant a cylindrical prosthesis. The third set of tests was to see if the conceptual unstable prosthesis allowed micromotion of 200 μm. Miniature silicone rubber and polyurethane resin [PUR(r)] springs were tested and a mock implantation in bone surrogate was conducted. Results: The results obtained from the first test show that it is easier to access the medullary canal of the femur from the knee side. The straight canal of the distal femur was also found to be more suitable to allow for micromotion than the curved canal of the proximal femur. The second test showed that we could implant a cylinder with a diameter of 2.3 mm and a length of 2.3 cm in the femoral canal. The third test showed that the conceptual prosthesis allowed for micromotion, but the spring’s material needs to be optimized. PUR(r)’s creep and compression set were too high. Silicone showed the most potential, because of its low compression set (permanent compressive deformation). However, the stiffness of the silicone needs to be increased and it showed high wear during fatigue testing with respect to the PUR(r). Conclusion: The conceptual prosthesis showed promise, but improvements on the spring material are necessary. The silicone can be made stiffer and altering the design can also increase the stiffness of the prosthesis. A flaw in the conceptual design is that micromotion is restricted in vivo, because the femoral prosthesis is abutted by the distal cortical bone. A change in the design of the prosthesis can remedy this problem. Another remaining challenge is to design a prosthesis which allows for localized application of wear debris particles and treatment solutions in the peri-prosthetic tissue, fully simulating the circumstances that occur during AL.Mechanical, Maritime and Materials EngineeringBiomechanical Engineerin
A Configurable Guide for Knee Arthroplasty
No full textIn total knee arthroplasty (TKA) the contact surfaces of the knee are replaced with prosthetic components. In order to fit the prosthetic components, the bones are shaped by making bone cuts. Patient specific surgical guides (PSSGs) are guides made from CT or MRI images to fit the patient’s anatomy. They guide the bone cuts. When bone deviations disturb the fit, commercially available PSSGs cannot be adjusted. Our goal is to design a reusable PSSG for TKA which can be configured for a planned alignment and corrected during surgery when unplanned bone deviations occur. Concepts for the functional problems are developed and combined into a final design consisting of three components: the guide, contact points and setting tool. The setting tool configures the contact points. The contact points are magnetically fixated to the guide’s base and can be removed when the fit is disturbed. Pins protrude from the contact points, indicating contact with the bone to evaluate the fit. We assess the ability of inexperienced and experienced subjects to recognize surface disturbances using the protruding pins. Subjects position the guide and are tasked to recognize if and where disturbances occur. With inexperienced users, the disturbed contact point is correctly recognized for 7 out of 26 disturbed experiments. A significant increase is found in the rotational error for placements with a disturbance. No significant increase is found for the translational error. With experienced users, the disturbed contact point is correctly recognized for 18 out of 26 disturbed experiments. No significant increase is found in the rotational and translational error for placements with a disturbance. Inexperienced users cannot recognize disturbances and reconfigure the guide. Experienced users can better recognize disturbances and reconfigure the guide. When disturbances were not correctly recognized by experienced users, the disturbance had only a small effect on the alignment. We recommend to correct the perceived backlash of the contact points and stiffen the guide design. Training of the test subjects is suggested when new experiments are performed.BMEBiomedical EngineeringMechanical, Maritime and Materials Engineerin
A New Approach to Reduce Positional Errors of Surgical Guides for Arthroplasty
No full textOrthopaedic surgeons can be assisted by Patient Specific Surgical Guides (PSSGs) during the determination of prostheses’ alignment in joint replacement surgeries. These guides are designed preoperatively – using Magnetic Resonance Imaging (MRI) or Computer Tomography (CT) – to have a matching contact surface with the patient’s bone. This enables the surgeon to place the guide in a uniquely planned position intraoperatively. Saw slots and drill holes are incorporated in PSSGs to create the crucial saw planes and drill holes for prostheses positioning. Tissues not detected by MRI or CT cannot be accounted for in the design of the guide’s matching surface. When such undetected tissues are present at the bone contact, they can introduce a positional error of the surgical guide. In our study multiple concepts are created which possibly decrease the positional error. The choice is made to develop a rigid and a compliant pin-based guide. Pin-based guides are configurable and thus suitable for multiple patients, since a patient-specific fit can be created. When relatively much contact points are used for the fit, compliant pins are able to absorb local irregularities. Therefore, a compliant guide can result in a lower positional error when a contact is placed onto an undetected tissue. Using more contact points will increase the ability of a compliant guide to result in a lower positional error. The two guide types are compared to their sensitivity to bony deviations in an experimental validation. The guides are placed onto a printed distal femur bone model with bony deviations. The actually reached position is measured using the optical tracking system Qualisys and is compared to the obtained position without bony deviations. For each guide four contact sets are tested to investigate the effect of the number of contact points. For validation of the experimental data, the positional error is calculated for the rigid guide with six contact points using an analytical model. Analysis of the measurement data results in a significantly lower rotational error for compliant guides compared to rigid guides. No significance is found between the translations of the two guide types. Further development of the compliant guide can be considered, since a significantly lower rotational error is obtained.BMEBioMechanical EngineeringMechanical, Maritime and Materials Engineerin
Inducible Displacement of a Knee Implant: A finite element study and validation of a loose and fixed tibial component
No full textIntroduction. Aseptic loosening is indicated as the main cause of knee implant failure. Despite all currently used techniques, it remains challenging to diagnose an aseptic loose knee implant. A promising technique to reveal aseptic loose related implant motions is inducible displacement (ID). ID measurements are used to detect implant motion relative to the bone. To diagnose a loose implant via ID, motion thresholds are required. Such thresholds are dependent on a number of subject specific factors including bone material, loading conditions, used implant and interface contact properties between implant and bone. Such thresholds do still not exist. As a first step towards subject specific motion thresholds, a finite element (FE) model can be used to investigate the factors affecting ID. Objective. To set-up and to validate a finite element model that can be used to simu-late inducible displacements of a tibial component of a knee implant. Method. As a basis for the finite element modelling, a previously performed experimentally study was used. This study provides data and material to build two finite element models. One model represents an aseptic loose (i.e., silicone layer between implant and bone) tibial component and a model represents a fixed (i.e., cemented) tibial component. FE-models were based on quantitative computed tomography (QCT) scans of the cadaveric tibiae. The experiments were simulated on the FE-models and the ID compared to the experimentally determined ID. Inducible displacements were expressed in terms of rotations and translations. Sensitivity analyses were performed in order to investigate the effects of assumptions during the modelling process on ID. The following assumptions were analyzed; bone material properties, load application points, interface contact properties, silicone layer stiffness and cement material properties. Results. Loose implant; translations due to top implant loads were found in good agreement to the experimental translations. FE determined rotations were considerable higher. Rotations and translations due to side implant loads were considerably less in the FE-model. Fixed implant: No clear agreement was found after comparing experimentally and FE determined displacements in the cemented implant model. A sensitivity analysis reveals that the implementation of interface interaction properties led to a considerable reduction of the error between experimentally and FE determined ID. A sensitivity analysis reveals also that experimental loading conditions were not correctly applied leading to a considerable increase of implant rotations. Effects of variations of bone material properties on ID are found negligible. Conclusion. Two FE-models were build. A model representing a loose implant and a model representing a fixed implant. This study shows that: i) The implementation of interface interaction properties contributes to a considerable improvement of realistic FE determined ID. ii) Experimental data used to validate FE-simulations should be sufficiently accurate to analyze a cemented implant and be suitable to implement in a FE-model. iii) Bone material properties have a small influence on ID and might be implemented in a simplified way. Further research is required to optimize the validation of the FE-models.Tissue Biomechanics & ImplantsBiomedical EngineeringMechanical, Maritime and Materials Engineerin
Design of High Viscosity Cement Gun for Vertebroplasty
No full textVertebroplasty is a minimally invasive procedure for treating spine. Cement leakage is problem occurring from usage of low viscosity bone cements. High viscosity bone cements are difficult to inject with current design of cement gun due to very high injection forces. A new design of cement gun is developed for injection of high viscosity bone cements with low injection forces.BMEBioMechanical EngineeringMechanical, Maritime and Materials Engineerin
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