The shape of the mitral valve annulus is used in diagnostic and modeling applications, yet methods to accurately and reproducibly delineate the annulus are limited. This paper presents a mitral annulus segmentation algorithm designed for closed mitral valves which locates the annulus in three-dimensional ultrasound using only a single user-specified point near the center of the valve. The algorithm first constructs a surface at the location of the thin leaflets, and then locates the annulus by finding where the thin leaflet tissue meets the thicker heart wall. The algorithm iterates until convergence metrics are satisfied, resulting in an operator-independent mitral annulus segmentation. The accuracy of the algorithm was assessed from both a diagnostic and surgical standpoint by comparing the algorithm's results to delineations made by a group of experts on clinical ultrasound images of the mitral valve, and to delineations made by an expert with a surgical view of the mitral annulus on excised porcine hearts using an electromagnetically tracked pointer. In the former study, the algorithm was statistically indistinguishable from the best performing expert (p=0.85) and had an average RMS difference of 1.81+/-0.78 mm to the expert average. In the latter, the average RMS difference between the algorithm's annulus and the electromagnetically tracked points across six hearts was 1.19+/-0.17 mm .

The manipulation of fast-moving, delicate tissues in beating heart procedures presents a considerable challenge to the surgeon. A robotic force tracking system can assist the surgeon by applying precise contact forces to the beating heart during surgical manipulation. Standard force control approaches cannot safely attain the required bandwidth for this application due to vibratory modes within the robot structure. These vibrations are a limitation even for single degree-of-freedom systems that drive long surgical instruments. These bandwidth limitations can be overcome by the incorporation of feed-forward motion terms in the control law. For intracardiac procedures, the required motion estimates can be derived from 3-D ultrasound imaging. Dynamic analysis shows that a force controller with feed-forward motion terms can provide safe and accurate force tracking for contact with structures within the beating heart. In vivo validation confirms that this approach confers a 50% reduction in force fluctuations when compared with a standard force controller and a 75% reduction in fluctuations when compared with manual attempts to maintain the same force.

Search and rescue robots often use tethers to provide power and communication, but tethers get caught on debris and small robots have difficulty with the added drag of the tether. This work investigates a self-actuating tether capable of remaining free while traversing obstacles. We present a physical model of the pressure transients actuated tether. The model relates forward motion of the tether (independent of a dragging force) to the relevant design parameters of hose stiffness, flow diameter, tether length, applied pressure, and valve selection. We present an experiment to test and validate our model. The experimental results correspond within 15% to the expected values from our analysis and also validate the functional dependence of our model on the design parameters

Integration of the correct tactile and kinesthetic force feedback response with an accurate computational model of a compliant environment is a formidable challenge. We examine several design issues that arise in the construction of a compliance renderer, specifically the interaction between impedances of tactile displays, impedances of robot arms, and the computational model. We also describe an implementation of a compliance rendering system combining a low-impedance robot arm for large workspace kinesthetic force feedback, a high-impedance shape display for distributed tactile feedback to the finger pad, and a real-time finite element modeler. To determine the efficacy of the integration of tactile and kinesthetic force feedback components, we conducted a study examining the user’s ability to discriminate stiffness. Subjects were able to reliably detect a 20% difference in rendered material stiffness using our compliance rendering system.

Combining teletaction systems with telemanipulation systems promises to enhance task performance when interacting with remote environments. However, the force scaling inherent in the telemanipulation system affects the ability of the user to control the exploration force. The quality of the tactile signal is therefore impacted, affecting performance in tasks that benefit from spatially distributed force information. We compare performance localizing an embedded lump in a compliant environment using a telemanipulated teletaction system versus a directly manipulated teletaction system. Lump localization accuracy was found to be the same; however, time required to localize the lump was up to 150% longer for the telemanipulation trials. Based upon our results, we conclude that the ability to maintain an appropriate force in the remote environment is necessary to take full advantage of the spatially distributed force information from the tactile sensor.

In the world of search and rescue robotics, particularly for search, smaller is better. Small robots can get into tighter places and are more maneuverable. With diminishing size, however, providing adequate power and communications becomes a problem. Communication is problematic if the search site is a collapsed building were transmitted signals have to travel through layers of concrete and steel. Tethers are good for providing power and communication, but tethers get caught and small robots have difficulty with the added drag of the tether. This work proposes a self-actuating tether capable of moving its own weight and remaining free while traversing around corners. Tether motion is due to induced high pressure water transients formed by rapidly arresting flow through the tether. A number of tests performed on a constructed tether prototype are presented. A simplified model of the water transients to better understand design parameters is outlined and simulated, and force measurements are collected to validate the simulation results.

Presents a method for localizing miniature mobile robots (Scouts) using dynamic contours. An observer robot with a camera follows the miniature robot as it moves and jumps in the workspace. Dynamic contours are very effective in tracking the fast accelerations and decelerations of the Scout robot. We show initial experimental results with particular emphasis on the task of monitoring a Scout during jumps.

The classical active contour model has two basic internal forces: tension and curvature. These forces are included to provide cohe sion, equal control point spacing, and locally smooth shape. These classical internal forces have undesirable attributes that are in conflict with these original desired characteristics. Tension evenly spaces the control points, but also causes the models to collapse in weak image gradients. Curvature produces locally smooth curvature, but it does so by forcing the model toward a straight line. The paper returns to the original active contour model motivations to reformulate these internal forces. The desired properties are achieved without the introduction of unwanted model behavior A new spacing force and a new constant change in curvature force are introduced and their performance characteristics are discussed. The paper includes experimental results that demonstrate the efficacy and performance of the proposed reformulations.

Grasping is one of the most fundamental and challenging tasks in robotics. Applications range from space missions (e.g., collection of rock samples) to industrial automation. In this work, we use a camera mounted on the end-effector of a manipulator to grasp an unknown object in the workspace. A novel deformable contour model is used to determine plausible grasp axes of the target object. Potential grasp point pairs are generated, ranked based upon measurements taken from the contour, and a vision-guided grasp of the object using the highest ranked grasp point pair is executed. Several experimental results are presented.

HOLDeR (Hierarchical, Object-centered, Learning Dextrous Robotics) is a new approach to the problem of object-centered task execution. It balances stored object knowledge with flexibility to produce a system that is capable of manipulating a wide variety of known and unknown objects. HOLDeR utilizes a layered approach to sensory-motor coordination that enables a robot to use as much object-specific data as possible, given time and computational constraints. The architecture also incorporates learning to allow the system to adapt to new objects and new classes of objects that it encounters. HOLDeR is based upon a modification of an active deformable model technique called dynamic pressure snakes. The techniques can be adapted to a variety of robotic tasks.