Surgical repair of the mitral valve is preferred in most cases over valve replacement, but replacement is often performed
instead due to the technical difficulty of repair. A surgical planning system based on patient-specific medical images that
allows surgeons to simulate and compare potential repair strategies could greatly improve surgical outcomes. In such a
surgical simulator, the mathematical model of mechanics used to close the valve must be able to compute the closed state
quickly and to handle the complex boundary conditions imposed by the chords that tether the valve leaflets. We have
developed a system for generating a triangulated mesh of the valve surface from volumetric image data of the opened
valve. We then compute the closed position of the mesh using a mass-spring model of dynamics. The triangulated mesh
is produced by fitting an isosurface to the volumetric image data, and boundary conditions, including the valve annulus
and chord endpoints, are identified in the image data using a graphical user interface. In the mass-spring model, triangle
sides are treated as linear springs, and sides shared by two triangles are treated as bending springs. Chords are treated as
nonlinear springs, and self-collisions are detected and resolved. Equations of motion are solved using implicit numerical
integration. Accuracy was assessed by comparison of model results with an image of the same valve taken in the closed
state. The model exhibited rapid valve closure and was able to reproduce important features of the closed valve.
This study presents a multi-modality image registration method that evaluates left atrial scarring after radiofrequency
(RF) ablation for pulmonary vein (PV) isolation. Our group has recently developed a delayed enhancement magnetic
resonance imaging (DE-MRI) method with the potential to visualize and monitor non-invasively post-ablation scarring
in the left atrium and the PV ostia. We wished to compare the 3D configuration of scarring in the DE-MRI image and the
ablation points recorded by electroanatomical mapping (EAM) system, hypothesizing that scarring detected by DE-MRI
overlaps with ablation points recorded by the EAM system used in the procedure.
<b>Methods and Results:</b> Three data sets, DE-MRI images and pulmonary vein MR angiography (PV-MRA) images, and
EAM data (CARTO-XP, Biosense-Webster, Inc., Diamond Bar, CA) from a patient who underwent PV ablation, were
used for the multi-modal image registration. Contrast-enhanced MR imaging was performed 38 days after the ablation
procedure. PV-MRA and DE-MRI were fused by intensity-based rigid registration. Scar tissue was extracted from the
DE-MRI images using multiple threshold values. EAM data was further fused with segmented PV-MRA by the iterative
closest point algorithm (ICP). After registration, the distance from PV-MRA to the scar was 2.6 ± 2.1 mm, and from
ablation points to the surface of the scar was 2.5 ± 2.3 mm. The fused image demonstrates the 3D relationship between
the PV ostia, the scar and the EAM recording of ablation points.
<b>Conclusion:</b> Multimodal data fusion indicated that the scar tissue lesion after PV isolation showed good overlap with the
The recent development of real-time 3D ultrasound enables intracardiac beating heart procedures, but the distorted appearance of surgical instruments is a major challenge to surgeons. In addition, tissue and instruments have similar gray levels in US images and the interface between instruments and tissue is poorly defined. We present an algorithm that automatically estimates instrument location in intracardiac procedures. Expert-segmented images are used to initialize the statistical distributions of blood, tissue and instruments. Voxels are labeled of voxels through an iterative expectation-maximization algorithm using information from the neighboring voxels through a smoothing kernel. Once the three classes of voxels are separated, additional neighboring information is used to give spatial information based on the shape of instruments in order to correct for misclassifications. We analyze the major axis of segmented data through their principal components and refine the results by a watershed transform, which corrects the results at the contact between instrument and tissue. We present results on 3D in-vitro data from a tank trial, and 3D in-vivo data from a cardiac intervention on a porcine beating heart. The comparison of algorithm results to expert-annotated images shows the correct segmentation and position of the instrument shaft.
Parametric active deformable models for image-based segmentation offer a distinct advantage over level sets: speed. This paper presents an extension to active deformable models that makes real-time volume segmentation possible on mid-range off-the-shelf hardware and without the use of specialized graphics hardware. The proposed method uses region-based parametric deformable models. A region-based parametric model, represented by a polygon, must remain non-self intersecting (simple) while undergoing deformation. The simplicity constraint can be enforced by allowing topological changes or by restricting motions of the curve. In either case, intersections of curve segments must be detected otherwise catastrophic divergence results. Good performance relies on the efficiency of the intersection check operation. This paper presents a parameter-free and efficient technique for on-line simplicity checking of polygons undergoing motion. We present timing results validating our approach; in particular, we segment 3-D ultrasound data at 20 volumes per second.
A computer-based algorithm has been developed which uses preoperative images to provide a surgeon with a list of feasible port triplets ranked according to tool dexterity and endoscopic view quality at each surgical site involved in a procedure. A computer simulation allows the surgeon to select from among the proposed port locations. The procedure selected for the development of the system consists of a coronary artery bypass graft (CABG). In this procedure, the interior mammary artery (IMA) is mobilized from the interior chest wall, and one end is attached to the coronary arteries to provide a new blood supply for the heart. Approximately 10-20 cm is dissected free, using blunt dissection and a harmonic scalpel or electrocautery. At present, the port placement system is being evaluated in clinical trials.
Certain minimally invasive surgical procedures involve the treatment of highly precise target locations within deformable tissues. While preoperative MRI and CT models can be used for surgical planning, they provide only coarse guidance during surgery due to their limited resolution and owing to tissue deformation. Ultrasound imaging is a promising means of obtaining real-time intraoperative data for target localization that is particularly well suited to minimally invasive surgery due to its portability, speed, and safety. This paper presents a system, in which ultrasound images are used to guide a manipulator to a surgical site. Electromagnetic tracking of the ultrasound probe is used to orient the images. These are then segmented in real time to determine target locations. Finally, target coordinates are used to produce control inputs to drive the manipulator to the target site. The potential of the approach is demonstrated experimentally using a manipulator arm, phantom target, and commercial ultrasound machine.
This paper presents the design and testing of a multi-channel vibrotactile display composed of cylindrical handle with four embedded vibrating elements driven by piezoelectric beams. The experimental goal of the paper is to analyze the performance of the device during a teleoperated force controlled task. As a test bed, a teleoperator system composed of two PHANToM haptic devices is used to trace a rectangular path while the operator attempts to maintain a constant force at the remote manipulator's tip. Four sensory modalities are compared. The first is visual feedback alone. Then, visual feedback is combined with vibration, force feedback, and force feedback plus vibration. Comparisons among these four modes are presented in terms of mean force error. Results show that force feedback combined with vibration provide the best feedback for the task. They also indicate that the vibrotactile device provides a clear benefit in the intended application, by reducing the mean force errors by 35 percent when compared to visual feedback alone.
In teleoperation, automatic identification of remote environment properties such as object weight, size, and friction can assist the teleoperator in determining optimal manipulation strategies. Similarly, virtual training systems can be calibrated using such an automatic identification procedure. For those properties which can be described by parameterization constraint equations, this paper provides a method by which the active constraints can be determined during each portion of the remote manipulator's data stream. The parameterized properties can then be estimated from the appropriate data stream segments. The approach is validated for peg-in-hole insertion using a desktop teleoperator system.
Among the mechanical parameters that are important for dexterous manipulation, shape is useful for both object recognition and control purposes. To investigate the role of shape information in telemanipulation we have created a tactile shape display. This prototype consists of a regular 6 X 4 array of pin elements or `tactors' which rest against the operator's finger tip. Shape memory alloy wires raise individual tactors to approximate the desired surface shape on the skin. We have implemented a feedforward control law and air- cooling that improves the bandwidth of the otherwise slow SMA wires. The hysteretic and nonlinear nature of the SMA actuators has also led us to implement a closed loop controller with position feedback using an optical emitter-receiver pair. The resulting performance of the SMA actuators has a -3 dB bandwidth point between 6 and 7 Hz. We have interfaced the display with a capacitive tactile array sensor and we are able to convey simple shapes from a remote environment through the display. The results of simple tactile feature localization experiments show the ability of the shape relay system to convey shape information.
In this paper we examine the role of high-frequency vibrations in the performance of a task in which subjects had to alternately tap in between two strips without applying excessive forces. We conducted three different experiments. In the first two experiments, subjects performed the task using two different actuated styli: a lightweight stylus and a massive stylus. In the first experiment, subjects performed the task using the lightweight stylus with and without masking (provided by continuous actuation of the solenoid). The number of successful taps decreased by a factor of 6.0 when the subjects used the stylus with masking. In the second experiment the massive stylus was used in two different modes. In one mode the solenoid was not actuated and in the second mode, the display mode, the solenoid produced a burst of vibrations when triggered by an electrical switch that closed when the stylus was in contact with the target strips. The performance of the subjects increased by a factor of 1.6 when they used the stylus with the display. These results indicate that people use high-frequency information during manipulation tasks and that a high-frequency display can be used to convey this information.
In this paper we examine the role of force bandwidth in performance of close-tolerance peg-in- hole insertion. The experiments use a two fingered teleoperated hand system with finger-level force feedback. Low-pass filters are used to vary the frequency content of the force feedback signal. Task completion times and error rates decrease as force reflection bandwidth increases. Most of the benefit appears between 2 and 8 Hz bandwidth, although some improvement is seen to 32 Hz, the highest frequency examined. These experiments also indicate that even low bandwidth force feedback improves the operator's ability to moderate task forces. However, force feedback does not enable to the operator to minimize grasp force, since this requires information about the friction at the contact between the grasped object and the slave finger tip.