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This paper presents a method for the computation of 3D flow in 4D (3D spatial+time) Transesophageal Echocardiography (4D TEE). 4D echocardiography is the only modality that allows real-time 3D imaging of the heart, at rates that are sufficiently high to characterize the very fast motion of key anatomical structures, such as the mitral and aortic valves or the left ventricle. The method described in this paper relies on a recently introduced variational optical flow approach. We applied the method to estimate the velocity field of myocardium in the left heart. Real intraoperative 4D TEE data was used and the method yielded good quantitative and qualitative preliminary results. This method has many applications, including elastography, biomechanical modeling, and automated diagnostics.

In this paper, we propose a graph-based method for fullyautomatic segmentation of the left ventricle and atrium in 3D ultrasound (3DUS) volumes. Our method requires no user input and can segment volumes with open and closed mitral valves. We utilize the radial symmetry transform to determine a central axis along which the 3D volume is warped into a cylindrical coordinate space. A graph is constructed for the volume in this space and a min-cut algorithm is applied to segment the left ventricle and atrium from the background. Since segmentation in the cylindrical coordinate space is defined as finding a boundary between the left (interior) and right (exterior) sides, we obviate the need for user specified seeds. The segmented results are transformed back to the Cartesian coordinate space. Experiments using intraoperative 3D ultrasound data show promising results.

A description of mitral valve function requires both an accurate anatomical description of the three-dimensional (3D) structure as well as a description of the leaflets' rapid motion. Current two-dimensional (2D) ultrasound imaging is unable to capture the 3D anatomy and 3D imaging suffers from severely reduced temporal resolution. We present a method to utilize two sequential 3D transesophageal echocardiographic (TEE) ultrasound acquisitions with a temporal delay to create a dataset that captures the 3D anatomical description of the valve and has a higher temporal resolution. The enhanced dataset should provide better information for modeling the motion of the mitral vale.

Direct haptic feedback and graphical force feedback have both been hypothesized to improve the performance of robot-assisted surgery. In this study we evaluate the benefits of haptic and graphical force feedback on surgeon performance and tissue exploration behavior during a teleoperated palpation task of artificial tissues. Seven surgeon subjects (four experienced in robot-assisted surgery) used a 7-degree-of-freedom teleoperated surgical robot to identify a comparatively rigid rigid target object (representing a calcified artery) in phantom heart models using the following feedback conditions: (1) direct haptic and graphical feedback, (2) direct haptic only, (3) graphical feedback only, and (4) no feedback. To avoid the problems of force sensing in a minimally invasive surgical environment, we use a position-exchange controller with dynamics compensation for direct haptic feedback and a force estimator displayed via tool-tip tracking bar graph for graphical force feedback. Although the transparency of the system is limited with this approach, results show that direct haptic force feedback minimizes applied forces to the tissue, while coupled haptic and graphical force feedback minimizes subject task error. For experienced surgeons, haptic force feedback substantially reduced task error independent of graphical feedback.

Haptic virtual fixtures have been shown to improve user performance and increase the safety of robot-assisted tasks, particularly for surgical applications. However, little research has studied virtual fixtures that provide moving force constraints based on motion of the environment, e.g., organ movement due to heartbeat or respiration. This work discusses design considerations of moving forbidden-region virtual fixtures and presents two methods of implementation: predicted-position and current-position virtual fixtures. Human subject experiments were performed to determine the effectiveness of moving virtual fixtures when interacting with an object in motion using a teleoperator. Results show that moving virtual fixtures can help improve user precision and decrease the amount of force applied.

In this paper, we develop and test a 6-degree-of-freedom surgical teleoperator that has four possible modes of operation: (1) direct force feedback, (2) graphical force feedback, (3) direct and graphical force feedback together, and (4) no force feedback. In all cases, visual feedback of the: environment is provided via a head-mounted display. A position-position controller with local dynamic compensators provides the direct force feedback. The graphical force feedback is overlaid on the environment image, and displays a bar whose height and color is related to the environment force estimated using the current applied to the actuators of the patient-side arm. We evaluate the performance of the teleoperator modes in assisting a user to find the location of stiff objects hidden inside a soft material, similar to a calcified artery hidden in heart tissue and a tumor in the prostate. Seven people used the teleoperator t:o perform palpation in these materials. Results showed that direct force feedback mode minimizes palpation task error for the heart model.