Intracardiac ultrasound is an important imaging modality in guiding structural heart and electrophysiology procedures. The small size of the intracardiac echocardiography (ICE) catheters which enables easy access to the heart chambers without general anesthesia limits the image resolution and penetration depth as the aperture size is geometrically constrained. These constraints can be avoided by using a folded 2D ICE array that can be unfolded inside the heart to provide a large 2D aperture with dimensions not limited by the diameter of the catheter. This will eliminate the need for imaging from areas such as the coronary sinus and right ventricular outflow tract reducing the risk of cardiac perforation, tamponade, and valve damage. Among the significant challenges in the implementation of a real-time 3D imaging ICE catheter with a folded 2D array which include low profile 2D arrays with integrated electronics, deployment errors and their compensation is addressed in this application. Our simulations of foldable 2D sparse Vernier arrays are encouraging, as in many cases when effective angular folding and twisting errors are compensated below 1, the image quality is preserved. For real time measurement and compensation of these errors, we propose integration of an electromagnetic orientation sensor to the imaging array panels for real-time orientation information. These simple coil based systems are already used in many catheterization labs for catheter tracking and anatomical mapping in electrophysiology procedures. In this application, we will design, fabricate and test 2D CMUT based ICE arrays with integrated tracking coils. We will then use these arrays and sensors on specially prepared substrates mimicking various deployment errors to measure the performance of the tracking coils in compensating deployment errors during transmit beamforming. The data will also be used to improve the simple time delay compensation methods used in earlier simulations. Our main metric for success will be reducing the effective overall deployment errors in real-time so that the lateral beam width is conserved and the increase in the far side lobe levels is kept lower than 6dB to result in acceptable degradation in the contrast resolution as compared to a single panel 2D imaging array of the same size.
Using a foldable large aperture 2D array in an intracardiac ultrasound catheter will result in volumetric images of the heart anatomy with high resolution and wide field of view, improving the ease of use and efficacy of this important tool in structural heart and electrophysiology procedures, reducing procedure times and more importantly the risk of cardiac tissue damage.
|Shieh, Bernard; Sabra, Karim G; Degertekin, F Levent (2018) A Hybrid Boundary Element Model for Simulation and Optimization of Large Piezoelectric Micromachined Ultrasonic Transducer Arrays. IEEE Trans Ultrason Ferroelectr Freq Control 65:50-59|