Anderson Maciel

Using the PhysX engine for Physics-based Virtual Surgery with Force Feedback

The development of modern surgical simulators is highly challenging, as they must support complex simulation environments. The demand for higher realism in such simulators has driven researchers to adopt physics‐based models, which are computationally very demanding. This poses a major problem, since real‐time interactions must permit graphical updates of 30 Hz and a much higher rate of 1 kHz for force feedback (haptics). Recently several physics engines have been developed which offer multi‐physics simulation capabilities, including rigid and deformable bodies, cloth and fluids. While such physics engines provide unique opportunities for the development of surgical simulators, their higher latencies, compared to what is necessary for real‐time graphics and haptics, offer significant barriers to their use in interactive simulation environments.

Anatomy-based joint models for virtual human skeletons

This paper describes a new joint model for articulated human skeletons. The model is based in human anatomy and was conceived for use in medical applications. In this model, we try to overcome some limitations of other models used in computer graphics. For validation, we compared a knee modeled by our approach with a simulator, a plastic model of a knee, and images taken during a video-arthroscopy.

Development of the VBLaST™: a virtual basic laparoscopic skill trainer

The FLS training tool box has now been adopted by the Society of Gastrointestinal Endoscopic Surgeons (SAGES) as an official training tool for minimally invasive procedures.

Efficient collision detection within deforming spherical sliding contact

Handling the evolving permanent contact of deformable objects leads to a collision detection problem of high computing cost. Situations in which this type of contact happens are becoming more and more present with the increasing complexity of virtual human models, especially for the emerging medical applications. In this context, we propose a novel collision detection approach to deal with situations in which soft structures are in constant but dynamic contact, which is typical of 3D biological elements. Our method proceeds in two stages: First, in a preprocessing stage, a mesh is chosen under certain conditions as a reference mesh and is spherically sampled. In the collision detection stage, the resulting table is exploited for each vertex of the other mesh to obtain, in constant time, its signed distance to the fixed mesh. The two working hypotheses for this approach to succeed are typical of the deforming anatomical systems we target: First, the two meshes retain a layered configuration with respect to a central point and, second, the fixed mesh tangential deformation is bounded by the spherical sampling resolution. Within this context, the proposed approach can handle large relative displacements, reorientations, and deformations of the mobile mesh. We illustrate our method in comparison with other techniques on a biomechanical model of the human hip joint.

LOP-cursor: Fast and precise interaction with tiled displays using one hand and levels of precision

We present levels of precision (LOP) cursor, a metaphor for high precision pointing and simultaneous cursor controlling using commodity mobile devices. The LOP-cursor uses a two levels of precision representation that can be combined to access low and high resolution of input. It provides a constrained area of high resolution input and a broader area of lower input resolution, offering the possibility of working with a two legs cursor using only one hand. LOP-cursor is designed for interaction with large high resolution displays, e.g. display walls, and distributed screens/computers scenarios. This paper presents the design of the cursor, the implementation of a prototype, and user evaluation experiments showing that our method allows both, the acquisition of small targets, and fast interaction while using simultaneous cursors in a comfortable manner. Targets smaller than 0.3 cm can be selected by users at distances over 1.5 m from the screen with minimum effort.

Efficient liver surgery planning in 3D based on functional segment classification and volumetric information

Anatomic hepatectomies are resections in which compromised segments or sectors of the liver are extracted according to the topological structure of its vascular elements. Such structure varies considerably among patients, which makes the current anatomy-based planning methods often inaccurate. In this work we propose a strategy to efficiently and semi-automatically segment and classify patient-specific liver models in 3D. The method is based on standard CT datasets and allows accurate estimation of functional remaining liver volume. Experiments showing effectiveness of the method are presented, and quantitative and qualitative results are discussed.

Disambiguation Canvas: A Precise Selection Technique for Virtual Environments

We present the disambiguation canvas, a technique developed for easy, accurate and fast selection of small objects and objects inside cluttered virtual environments. Disambiguation canvas rely on selection by progressive refinement, it uses a mobile device and consists of two steps. During the first, the user defines a subset of objects by means of the orientation sensors of the device and a volume casting pointing technique. The subsequent step consists of the disambiguation of the desired target among the previously defined subset of objects, and is accomplished using the mobile device touchscreen. By relying on the touchscreen for the last step, the user can disambiguate among hundreds of objects at once. User tests show that our technique performs faster than ray-casting for targets with approximately 0.53 degrees of angular size, and is also much more accurate for all the tested target sizes.

Design and Evaluation of a Handheld-based 3D User Interface for Collaborative Object Manipulation

Object manipulation in 3D virtual environments demands a combined coordination of rotations, translations and scales, as well as the camera control to change the users viewpoint. Then, for many manipulation tasks, it would be advantageous to share the interaction complexity among team members. In this paper we propose a novel 3D manipulation interface based on a collaborative action coordination approach. Our technique explores a smartphone -- the touchscreen and inertial sensors -- as input interface, enabling several users to collaboratively manipulate the same virtual object with their own devices. We first assessed our interface design on a docking and an obstacle crossing tasks with teams of two users. Then, we conducted a study with 60 users to understand the influence of group size in collaborative 3D manipulation. We evaluated teams in combinations of one, two, three and four participants. Experimental results show that teamwork increases accuracy when compared with a single user. The accuracy increase is correlated with the number of individuals in the team and their work division strategy.

Interacting with danger in an immersive environment: issues on cognitive load and risk perception

Any human-computer interface imposes a certain level of cognitive load to the user task. Analogously, the task itself also imposes different levels of cognitive load. It is common sense in 3D user interfaces research that a higher number of degrees of freedom increases the interface cognitive load. If the cognitive load is significant, it might compromise the user performance and undermine the evaluation of user skills in a virtual environment. In this paper, we propose an assessment of two immersive VR interfaces with varying degrees of freedom in two VR tasks: risk perception and basic object selection. We examine the effectiveness of both interfaces in these two different tasks. Results show that the number of degrees of freedom does not significantly affect a basic selection task, but it affects risk perception task in an unexpected way.

Efficient Surgical Cutting with Position-Based Dynamics

Simulations of cuts on deformable bodies have been an active research subject for more than two decades. However, previous works based on finite element methods and mass spring meshes cannot scale to complex surgical scenarios. This article presents a novel method that uses position-based dynamics (PBD) for mesh-free cutting simulation. The proposed solutions include a method to efficiently render force feedback while cutting, an efficient heat diffusion model to simulate electrocautery, and a novel adaptive skinning scheme based on oriented particles.https://extras.computer.org/extra/mcg2017030024s1.mp4