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The feasibility of catheter single-element ultrasound transducers for cardiac ablation has been shown previously. We describe the design and testing of catheter-sized linear phased arrays transducers for ultrasound ablation. One array has 86 PZT-4 elements operating at 8 MHz and 5 MHz. The overall array size is 14.9 mm by 3.1 mm (10 Fr). The other array has 50 PZT-5 elements operating at 4 MHz and is 17 mm by 3.1 mm (10 Fr). In order to produce the intensity needed to create lesions in heart tissue, we modified a real-time, 3D scanner to produce 100 Vpp 256-cycle transmit pulses at a pulse repetition frequency of 14.1 kHz. This made it possible for the PZT-4 and PZT-5 transducers to produce ISPTA of 3.26 W/cm2 and 142 W/cm2, respectively. When driving the transducers at high duty factor, the transmit circuitry in the scanner was damaged. A mechanically-focused transducer with the same dimensions as the PZT-4 transducer was built. When transmitting continuously at 9 MHz, it produced an ISPTA of 29.3 W/cm2. This created a lesion 5 mm across and 5 mm deep in beef tissue while raising the focal temperature 23 degrees C. Ablation is within the capabilities of a catheter phased array transducer integrated into a diagnostic ultrasound scanner.

A method for simulating the temperature rise due to acoustic heating from an ablation transducer is introduced. The size of lesions produced by this temperature rise is also modeled. First the intensity from the transducer is calculated using Field II. This intensity is scaled to a measured value and converted into acoustic heat generation. Finite element analysis is then used to find the temperature rise in tissue from this heat generation. Thermal dose is calculated and from that the size of any lesions may be predicted. We validate the model by comparing simulated results to experimental results from an ablation ring transducer. Temperatures were within 2°C of experiment after a 2 minute ablation. The simulation predicted a lesion size of 1.75 mm deep by 5.5 mm in diameter. The experimental average of four lesions was 1.75 mm deep by 4.6 mm in diameter. The model was then used to predict the temperatures and lesions created by an 86 element linear array transducer in various configurations.

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