Cardioscopic Tool-delivery Instrument for Beating-heart Surgery.

This paper describes an instrument that provides solutions to two open challenges in beating-heart intracardiac surgery - providing high-fidelity imaging of tool-tissue contact and controlling tool penetration into tissue over the cardiac cycle. Tool delivery is illustrated in the context of tissue removal for which these challenges equate to visualization of the tissue as it is being removed and to control of cutting depth. Cardioscopic imaging is provided by a camera and illumination system encased in an optical window. When the optical window is pressed against tissue, it displaces the blood between the camera and tissue allowing clear visualization. Control of cutting depth is achieved via precise extension of the cutting tool from a port in the optical window. Successful tool use is demonstrated in ex vivo and in vivo experiments.

Three-Degree-of-Freedom MR-Compatible Multisegment Cardiac Catheter Steering Mechanism.

This paper presents a novel MR-compatible 3-DOF cardiac catheter steering mechanism. The catheter's steerable structure is tendon driven and consists of miniature deflectable, helical segments created by a precise rapid prototyping technique. The created catheter prototype has an outer diameter of 9 Fr (3 mm) and a steerable distal end that can be deflected in a 3-D space via four braided high-tensile Spectra fiber tendons. Any longitudinal twist commonly observed in helical structures is compensated for by employing clockwise (CW) and counter clockwise (CCW) helical segments in an alternating fashion. A 280 µm flexible carbon fiber rod is used as a backbone in a central channel to improve the structure's steering and positioning repeatability. In addition to the backbone, a carbon fiber tube can be inserted into the structure to a varying amount capable of changing the structure's forcibility and, thus, providing a means to change the curvature and to modify the deflectable length of the catheter leading to an extension of reachable points in the catheter-tip workspace. A unique feature of this helical segment structure is that the stiffness can be further adjusted by appropriately tensioning tendons simultaneously. An experimental study has been conducted examining the catheter-tip trajectory in a 3-D space and its positioning repeatability using a 5-DOF magnetic coil tracking system. Furthermore, MRI experiments in a 1.5-T scanner confirmed the MR-compatibility of the catheter prototype. The study shows that the proposed concept for catheter steering has great potential to be employed for robotically steered and MR-guided cardiac catheterization.

Surface flattening of the human left atrium and proof-of-concept clinical applications.

Surface flattening in medical imaging has seen widespread use in neurology and more recently in cardiology to describe the left ventricle using the bull's-eye plot. The method is particularly useful to standardize the display of functional information derived from medical imaging and catheter-based measurements. We hypothesized that a similar approach could be possible for the more complex shape of the left atrium (LA) and that the surface flattening could be useful for the management of patients with atrial fibrillation (AF). We implemented an existing surface mesh parameterization approach to flatten and unfold 3D LA models. Mapping errors going from 2D to 3D and the inverse were investigated both qualitatively and quantitatively using synthetic data of regular shapes and computer tomography scans of an anthropomorphic phantom. Testing of the approach was carried out using data from 14 patients undergoing ablation treatment for AF. 3D LA meshes were obtained from magnetic resonance imaging and electroanatomical mapping systems. These were unfolded using the developed approach and used to demonstrate proof-of-concept applications, such as the display of scar information, electrical information and catheter position. The work carried out shows that the unfolding of complex cardiac structures, such as the LA, is feasible and has several potential clinical uses for the management of patients with AF.

MRI-compatible intensity-modulated force sensor for cardiac catheterization procedures.

This paper presents a novel, magnetic resonance imaging (MRI)-compatible, force sensor suitable for cardiac catheterization procedures. The miniature, fiber-optic sensor is integrated with the tip of a catheter to allow the detection of interaction forces with the cardiac walls. The optical fiber light intensity is modulated when a force acting at the catheter tip deforms an elastic element, which, in turn, varies the distance between a reflector and the optical fiber. The tip sensor has an external diameter of 9 Fr (3 mm) and can be used during cardiac catheterization procedures. The sensor is able to measure forces in the range of 0-0.85 N, with relatively small hysteresis. A nonlinear method for calibration is used and real-time MRI in vivo experiments are carried out, to prove the feasibility of this low-cost sensor, enabling the detection of catheter-tip contact forces under dynamic conditions.