Intracardiac catheter tracking using ultrasonic volumetric imaging fields

Introduction. Interventional cardiac electrophysiology procedures rely on catheters to diagnose and treat arrhythmias. Catheter visualization and guidance is typically accomplished using single-plane fluoroscopy combined with intracardiac electrograms. The need for accurate catheter positioning has become increasingly important in treating complex arrhythmias that require the formation of linear and compound radiofrequency (RF) ablation lesions. Efficacious treatment is hampered by the lack of three-dimensional (3-D) information and poor soft tissue contrast in fluoroscopic images. Safety risks to health care providers from prolonged exposure to ionizing radiation poses an additional problem. These inadequacies have created an impetus to improve catheter guidance. This dissertation expounds on real-time catheter tracking using volumetric ultrasound imaging fields.; Methods. A catheter-mounted transducer is used as a passive receiver in the volumetric ultrasound field. Predicted receive profiles are computed every one degree throughout the angular range and crosscorrelated with the measured receive profile to determine angular position. The time-of-flight between the imaging transducer and the catheter transducer provides range position. System hardware consists of custom-built peak detection circuitry, a field programmable gate array, a single board computer, and electronic marker injection circuitry. Simulated catheter data is used to determine the accuracy of this tracking technique. In vitro testing in a water tank is conducted to assess the system's resolution and continuous tracking ability. In vivo testing in ovine and porcine models is performed to determine system performance under realistic conditions.; Results. Results from simulation studies with 20-dB SNR exhibited a mean accuracy of 0.22 ± 0.13 mm at a 70-mm range. In vitro testing resulted in a resolution of 0.23 ± 0.11 mm at a range of 75 mm and a resolution of 0.47 ± 0.47 mm at a range of 97 mm. In vivo experiments using an electronically added position marker were conducted without fluoroscopy. Catheters were inserted into the heart and navigated to specific sites under ultrasound guidance. Ablation lesion locations were investigated postmortem and confirmed position predictions made from the electronic marker location in the images. The results from the in vivo studies showed that the catheter tracking system could be used in clinical procedures.