Real-Time 4D Ultrasound Reconstruction of Intracardiac Echo (ICE) Catheters for Procedure Guidance
Commercially available ultrasound imaging catheters, known as intracardiac echocardiography (ICE), have an ultrasound transducer in the tip for acquiring high-resolution images from within the heart during procedures. This is useful for reliable imaging in diagnosis, navigation, and treatment. ICE catheters, which are currently controlled manually, are extremely challenging to aim due to the complex relationship between handle knobs and imager motion. The difficulty in steering ICE has limited its use to a few critical tasks.
A robotic system for automatic ultrasound imaging during beating heart surgery can increase situational awareness, improve workflow, reduce procedure times, and reduce complications. Our system steers an ICE catheter to automatically image cardiac structures or working instruments (such as ablation catheters) inside the heart. Steering is controlled by using a closed-form solution for forward and inverse kinematics that calculates the direction of the side-facing ultrasound imaging plane. Accurate real-time pose control capabilities of our robotics system, coupled with GPU-accelerated image processing, enable 4D (3D+time) reconstruction of the 2D ultrasound images acquired from the ICE catheter during the procedure.
Additionally, the system can automatically monitor instruments that interact with cardiac tissue by localizing the instrument and rotating the ICE imager accordingly. This shows a high-quality ultrasound image of the instrument-tissue contact point.
The net benefits of the robotic system described here will include better situational awareness, leading to faster workflow, reduced procedure time, and fewer complications.
Researchers: Alperen Degirmenci
Ultrasound Imaging for Understanding Muscle Dynamics
Muscles are biological actuators that can act as motors, clutches, and dampers. Much like how mechanical systems have operating characteristics, the magnitude and economy of force generation in skeletal muscles are dependent on length, velocity, and the amount of activation. More traditional metrics, such as electromyography and inverse dynamics, are incapable of directly measuring many of these operating characteristics. We are using ultrasound imaging to directly measure how muscles respond to robotic assistance during walking. The approach to understanding human/machine interaction combines the research areas of computer vision, engineering, biomechanics, and muscle physiology. Drawing from expertise in the lab, we are developing improved ultrasound processing techniques for tracking and understanding muscle dynamics. Through understanding how muscles respond to exosuit assistance, we can then develop improved controls and enhance the response of both healthy and clinical users.
Researchers: Letizia Gionfrida, Alperen Degirmenci, Richard Nuckols
High Dynamic Range Ultrasound
High dynamic range (HDR) imaging is a popular computational photography technique that has found its way into every modern smartphone and camera. In HDR imaging, images acquired at different exposures are combined to increase the luminance range of the final image, thereby extending the limited dynamic range of the camera. Ultrasound imaging suffers from limited dynamic range as well; at higher power levels, the hyperechogenic tissue is overexposed, whereas at lower power levels, hypoechogenic tissue details are not visible. In this work, we apply HDR techniques to ultrasound imaging, where we combine ultrasound images acquired at different power levels to improve the level of detail visible in the final image.
We acquired ultrasound images of ex vivo and in vivo tissue at different acoustic power levels and combined them to generate HDR ultrasound (HDR-US) images. We evaluated the performance of five tone mapping operators using a similarity metric to determine the most suitable mapping for HDR-US imaging.
The ex vivo and in vivo results demonstrated that HDR-US imaging enables visualizing both hyper- and hypoechogenic tissue at once in a single image. The Durand tone mapping operator preserved the most amount of detail across the dynamic range.
Our results strongly suggest that HDR-US imaging can improve the utility of ultrasound in image-based diagnosis and procedure guidance.
Researchers: Alperen Degirmenci
Mitral Valve Segmentation from Clinical 4D Ultrasound
Visualization and characterization of the mitral valve are especially challenging given its complexity, fast movement, and limitations in current clinical imaging technologies. Oftentimes, acquiring detailed information requires extensive imaging and image processing, which can be time-consuming using current methods. This often forces clinicians to make a compromise between speed and completeness of information. We have therefore developed several ultrasound image enhancement and analysis methods to semi-automatically segment the mitral valve from clinical four-dimensional ultrasound and to improve the quality and usefulness of original ultrasound acquisitions.
Researchers: Robert J. Schneider
Real-time 3D Ultrasound Mosaicing and Visualization
We have developed a system for steering cardiac imaging catheters to automatically visualize heart structures and instruments. The goal of this system is to improve the efficacy, speed, and safety of imaging during catheter-based arrhythmia treatment procedures. Many cardiac arrhythmias can be effectively treated by radiofrequency (RF) catheter ablation, but the primary imaging modality during an ablation procedure is x-ray fluoroscopy, which does not effectively distinguish soft tissues and exposes patients and clinical staff to ionizing radiation.
Real-time visualization of intracardiac structures is needed to further improve the efficacy of catheter ablation procedures. Intracardiac echocardiography (ICE) catheters are routinely used during ablation procedures for their high-quality ultrasound soft tissue visualization. A major challenge during catheter ablation is the lack of acute lesion assessment, and ICE visualization of lesion growth has the potential to improve acute procedural outcomes. However, manual use of ICE requires specialized training and maintaining continued alignment of the imaging plane is a significant challenge. Existing robotic catheter systems enable teleoperation of catheter controls and reduce radiation exposure, but they do not solve the problem of steering an ICE imaging plane towards a desired structure.
In this study, our system manipulates an ICE catheter in a water tank to visualize a phantom. Multiple images are stitched together to create a volume of the target structure. This enablement of real-time visualization during catheter ablation has the potential to facilitate improved long-term treatment of cardiac arrhythmias.
Researchers: Alperen Degirmenci, Laura J. Brattain, and Paul Loschack
3D Ultrasound Image Processing and Instrument Tracking
We continue to expand our 3D Ultrasound image processing toolbox to better enable new intracardiac surgical procedures. For example, we developed a detection technique that identifies the position of the instrument within the ultrasound volume. The algorithm uses a form of the generalized Radon transform to search for long straight objects in the ultrasound image, a feature characteristic of instruments and not found in cardiac tissue. When combined with passive markers placed on the instrument shaft, the full position and orientation of the instrument are found in 3D space. This detection technique is amenable to rapid execution on the current generation of personal computer graphics processor units (GPUs). Our GPU implementation detected a surgical instrument in 31 ms, sufficient for real-time tracking at the 25 volumes per second rate of the ultrasound machine.
Researchers: Paul Novotny, Marius George Linguraru and Petr Jordan
