Towards a Reduced-Wire Interface for CMUT-Based Intravascular Ultrasound Imaging Systems

Abstract

Having intravascular ultrasound (IVUS) imaging capability on guide wires used in cardiovascular interventions may eliminate the need for separate IVUS catheters and expand the use of IVUS in a larger portion of the vasculature. High frequency capacitive micro machined ultrasonic transducer (CMUT) arrays should be integrated with interface electronics and placed on the guide wire for this purpose. Besides small size, this system-on-a-chip (SoC) front-end should connect to the back-end imaging system with a minimum number of wires to preserve the critical mechanical properties of the guide wire. We present a 40 MHz CMUT array interface SoC, which will eventually use only two wires for power delivery and transmits image data using a combination of analog-to-time conversion (ATC) and an impulse radio ultra-wideband (IR-UWB) wireless link. The proof-of-concept prototype ASIC consumes only 52.8 mW and occupies 4.07 mm2 in a 0.35-μm standard CMOS process. A rectifier and regulator power the rest of the SoC at 3.3 V from a 10 MHz power carrier that is supplied through a 2.4 m micro-coax cable with an overall efficiency of 49.1%. Echo signals from an 8-element CMUT array are amplified by a transimpedance amplifier (TIA) array and down-converted to baseband by quadrature sampling using a 40 MHz clock, derived from the power carrier. The ATC generates pulse-width-modulated (PWM) samples at 2 × 10 MS/s with 6 bit resolution, while the entire system achieved 5.1 ENOB. Preliminary images from the prototype system are presented, and alternative data transmission and possible future directions towards practical implementation are discussed.

Advances in Capacitive Micromachined Ultrasonic Transducers

“…Hence, reducing the number of channels becomes a necessity. Analog multiplexing of the transducer channels and applying synthetic aperture imaging can reduce the number of connections to as low as two [ 65 ] with some compromise in the imaging quality and frame rate. A more efficient approach is to integrate TX beamformers and analog multiplexers with the CMUT array at the catheter tip to reduce the cable count without compromising the image quality [ 48 , 66 , 67 ].…”

A High Sensitivity 20-MHz Endoscopic Transducer With Integrated Miniature Amplifier

“…For example, a 2D array transducer with integrated ASIC in a 10 Fr catheter was developed for real-time 3D intracardiac echocardiography [31]. Especially in the development of capacitive micromachined ultrasonic transducer (CMUT), because of its MEMS/CMOS-based process, the front-end circuits or ASIC is more and more adopted and integrated [32][33][34][35][36]. However, because the frontend circuits or ASIC chips are generally developed exclusively and mainly for multi-element ultrasound transducers, and they were not easy and suitable to be used with single-element transducer.…”

Photoacoustic Imaging with Capacitive Micromachined Ultrasound Transducers: Principles and Developments

“…The motivation to further develop CMUT for other application resulted from an immersion test where it has shown that CMUTs can provide a larger bandwidth over traditional piezoelectric transducers [25]. Since then CMUTs have been used in a variety of domains ranging from high-intensity focused ultrasound [26,27], ultrasound imaging [28,29,30,31,32,33], sensing application [34,35] to non-destructive testing [36]. Some of these applications and CMUT designs have been further adapted to advance CMUTs for PAI applications.…”