Errors of electrocardiographic inverse solutions are especially sensitive to the accuracy with which a heart model is constructed and placed within the torso. In an effort to reduce those errors, we have improved our previous methods for generating individualized heart models from ultrasound images. An ultrasound probe is tracked using an Immersion digitizer, allowing measurement of the orientation and position of each image. Images are tracked relative to the torso, which is also measured using the digitizer. The probe is calibrated by imaging a phantom consisting of multiple N-fiducials and computing a transformation between ultrasound coordinates and Immersion measurements. Using these methods, we have constructed a heart surface model from apical and parasternal images acquired at multiple rotations and tilts with a Terason 2000 imaging system. Accuracy of the methods is limited by multiple factors, including patient movement, tracking error, and image analysis. We plan to investigate these limitations and to extend these methods to model dynamic, time-varying heart shape and location. Such studies are critical for the development of individualized anatomies, which are crucial for continued advancement of inverse methods.

Keywords: Inverse electrocardiography, ultrasound, calibration, individualized anatomy