Integrated HIFU Drive System on a Chip for CMUT-Based Catheter Ablation System

Conventional High Intensity Focused Ultrasound (HIFU) is a therapeutic modality which is extracorporeally administered. In applications where a relatively small HIFU lesion is required, an intravascular HIFU probe can be deployed to the ablation site. In this paper, we demonstrate the design and implementation a fully integrated HIFU drive system on a chip to be placed on a 6 Fr catheter probe. An 8-element capacitive micromachined ultrasound transducer (CMUT) ring array of 2 mm diameter has been used as the ultrasound source. The driver chip is fabricated in 0.35 mu m AMS high-voltage CMOS technology and comprises eight continuous-wave (CW) high-voltage CMUT drivers (10.9 ns and 9.4 ns rise and fall times at 20 V-pp output into a 15 pF), an eight-channel digital beamformer (8-12 MHz output frequency with 11.25 degrees phase accuracy) and a phase locked loop with an integrated VCO as a tunable clock source (128-192 MHz). The chip occupies 1.85 x 1.8 mm(2) area including input and output (I/O) pads. When the transducer array is immersed in sunflower oil and driven by the IC with eight 20 Vpp CW pulses at 10 MHz, real-time thermal images of the HIFU beam indicate that the focal temperature rises by 16.8 degrees C in 11 seconds. Each HV driver consumes around 67 mW of power when driving the CMUT array at 10 MHz, which adds up to 560 m W for the whole chip. FEM based analysis reveals that the outer surface temperature of the catheter is expected to remain below the 42 degrees C tissue damage limit during therapy.