Catheter Ultrasound Phased-Array Transducers for Thermal Ablation: A Feasibility Study

Abstract

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.

Dual-Mode Intracranial Catheter Integrating 3D Ultrasound Imaging and Hyperthermia for Neuro-oncology: Feasibility Study

“…In this preliminary experiment, a 50 channel, 4.4 MHz PZT-5H, 17 mm × 3.1 mm linear array transducer previously described was used with electrical impedance matching circuits customized for each channel in order to maximize power transfer from the scanner to the transducer elements 52. The matching circuits were simple ‘L-section’ networks consisting of two reactive components: an inductor in series with the load, and a capacitor in parallel.…”

Progress in Ring Array Transducers for Real-Time 3D Ultrasound Guidance of Cardiac Interventional Devices

“…Real time display options include up to five image planes oriented at any desired angle, depth and thickness within the pyramidal scan as well as real time 3D volume rendering, 3D pulse wave Doppler and 3D color flow Doppler. In our laboratories at Duke during the last few years, we have significantly modified the Volumetrics scanner to use our prototype 2-D arrays for applications such as real time 3D transesophageal imaging [10], laparoscopic imaging [11], intracardiac and intravascular imaging with catheter transducers [12] at 5, 7, 10 [13] and 15 MHz [14]. No new modifications were needed for the transducers described in this paper to run on the VMI Model 1 scanner.…”

Dual-Mode Intracranial Catheter Integrating 3D Ultrasound Imaging and Hyperthermia for Neuro-oncology: Feasibility Study

“…In this pre lim i nary ex per i ment, a 50 chan nel, 4.4 MHz PZT-5H, 17 mm × 3.1 mm lin ear ar ray trans ducer pre vi ously de scribed was used with elec tri cal im ped ance-match ing cir cuits cus tom ized for each chan nel in or der to max i mize power trans fer from the scan ner to the trans ducer el e ments. 52 The match ing circuits were sim ple 'L-sec tion' net works con sist ing of two re ac tive com po nents: an in duc tor in se ries with the load and a ca pac i tor in par al lel. To de sign these net works, the sys tem (source) im ped ance and the cor re spond ing wa ter-cou pled trans ducer el e ment (load) im pedance were mea sured at the cho sen op er at ing fre quency, for each chan nel.…”