Virtual reality-enhanced partial body weight-supported treadmill training poststroke: feasibility and effectiveness in 6 subjects.

UNLABELLED: Walker ML, Ringleb SI, Maihafer GC, Walker R, Crouch JR, Van Lunen B, Morrison S. Virtual reality-enhanced partial body weight-supported treadmill training poststroke: feasibility and effectiveness in 6 subjects. OBJECTIVE: To determine whether the use of a low-cost virtual reality (VR) system used in conjunction with partial body weight-supported treadmill training (BWSTT) was feasible and effective in improving the walking and balance abilities of patients poststroke. DESIGN: A before-after comparison of a single group with BWSTT intervention. SETTING: University research laboratory. PARTICIPANTS: A convenience sample of 7 adults who were within 1 year poststroke and who had completed traditional rehabilitation but still exhibited gait deficits. Six participants completed the study. INTERVENTION: Twelve treatment sessions of BWSTT with VR. The VR system generated a virtual environment that showed on a television screen in front of the treadmill to give participants the sensation of walking down a city street. A head-mounted position sensor provided postural feedback. MAIN OUTCOME MEASURES: Functional Gait Assessment (FGA) score, Berg Balance Scale (BBS) score, and overground walking speed. RESULTS: One subject dropped out of the study. All other participants made significant improvements in their ability to walk. FGA scores increased from mean of 13.8 to 18. BBS scores increased from mean of 43.8 to 48.8, although a ceiling effect was seen for this test. Overground walking speed increased from mean of .49m/s to .68m/s. CONCLUSIONS: A low-cost VR system combined with BWSTT is feasible for improved gait and balance of patients poststroke.

Automated finite-element analysis for deformable registration of prostate images.

Two major factors preventing the routine clinical use of finite-element analysis for image registration are: 1) the substantial labor required to construct a finite-element model for an individual patient's anatomy and 2) the difficulty of determining an appropriate set of finite-element boundary conditions. This paper addresses these issues by presenting algorithms that automatically generate a high quality hexahedral finite-element mesh and automatically calculate boundary conditions for an imaged patient. Medial shape models called m-reps are used to facilitate these tasks and reduce the effort required to apply finite-element analysis to image registration. Encouraging results are presented for the registration of CT image pairs which exhibit deformation caused by pressure from an endorectal imaging probe and deformation due to swelling.

Parametric eye models.

The shape of anatomic objects often depends in complex ways on the shapes and locations of neighboring objects. Shape parameter networks provide an approach for representing shape dependencies and producing multi-object models that share consistent boundary definitions. This paper provides an overview of the modeling framework provided by shape parameter networks, and demonstrates their use through the development of a detailed multi-object eye model. The eye model presented contains analytically defined shape equations that produce models matching user-specified physical measurements such as cornea width, cornea thickness, anterior chamber angle, and eye axial length.

A software framework for surgical simulation virtual environments.

Surgical simulators are an integration of many models, capabilities, and functions. Development of a working simulator requires the flexibility to integrate various software models, to support interoperability, and facilitate performance optimizations. An object oriented framework is devised to support multithreaded integration of simulation, deformation, and interaction. A demonstration application has been implemented in Java, leveraging the features that are built into the language including multithreading, synchronization, and serialization. Future work includes expanding the capabilities of the framework with a broader range of model and interactive capabilities.

A simulation-based training system for surgical wound debridement.

A simulation-based training system for surgical wound debridement was developed and comprises a multimedia introduction, a surgical simulator (tutorial component), and an assessment component. The simulator includes two PCs, a haptic device, and mirrored display. Debridement is performed on a virtual leg model with a shallow laceration wound superimposed. Trainees are instructed to remove debris with forceps, scrub with a brush, and rinse with saline solution to maintain sterility. Research and development issues currently under investigation include tissue deformation models using mass-spring system and finite element methods; tissue cutting using a high-resolution volumetric mesh and dynamic topology; and accurate collision detection, cutting, and soft-body haptic rendering for two devices within the same haptic space.

Finite element model of cornea deformation.

Cornea surgeons have observed that changes in cornea curvature can follow cataract surgery and cause astigmatism. The placement of surgical incisions has been shown to influence these curvature changes. Though empirical data has been collected about this phenomenon, a biomechanical model has not been employed in predicting post-surgical outcomes. This work implemented an incised finite element model of the eye to investigate factors influencing corneal shape after surgery. In particular, the effects of eye muscle forces and intra-ocular pressure were simulated. Cornea shape change was computed via finite element analysis, and the resulting change in cornea curvature was measured by fitting quadratic curves to the horizontal and vertical meridians of the cornea. Results suggest that these two sources of deforming force counteract each other and contribute to astigmatism in perpendicular directions.

A velocity-dependent model for needle insertion in soft tissue.

Models that predict the soft tissue deformation caused by needle insertion could improve the accuracy of procedures such as brachytherapy and needle biopsy. Prior work on needle insertion modeling has focused on static deformation; the experiments presented here show that dynamic effects such as relaxation are important. An experimental setup is described for recording and measuring the deformation that occurs with needle insertion into a soft tissue phantom. Analysis of the collected data demonstrates the time- and velocity-dependent nature of the deformation. Deformation during insertion is shown to be well represented using a velocity-dependent force function with a linear elastic finite element model. The model's accuracy is limited to the period during needle motion, indicating that a viscoelastic tissue model may be required to capture tissue relaxation after the needle stops.