No abstract

In real-time catheter based 3D ultrasound imaging applications, gathering data from the transducer arrays is difficult as there is a restriction on cable count due to the diameter of the catheter. Although area and power hungry multiplexing circuits integrated at the catheter tip are used in some applications, these are unsuitable for use in small sized catheters for applications like intracardiac imaging. Furthermore, the length requirement for catheters and limited power available to on-chip cable drivers leads to limited signal strength at the receiver end. In this paper an alternative approach using Analog Time Division Multiplexing (TDM) is presented which addresses the cable restrictions of ultrasound catheters. A novel digital demultiplexing technique is also described which allows for a reduction in the number of analog signal processing stages required. The TDM and digital demultiplexing schemes are demonstrated for an intracardiac imaging system that would operate in the 4 MHz to 11 MHz range. A TDM integrated circuit (IC) with 8:1 multiplexer is interfaced with a fast ADC through a micro-coaxial catheter cable bundle, and processed with an FPGA RTL simulation. Input signals to the TDM IC are recovered with −40 dB crosstalk between channels on the same micro-coax, showing the feasibility of this system for ultrasound imaging applications.

This paper presents a single chip reduced-wire active catheter application-specific integrated circuit (ASIC), equipped with programmable transmit (Tx) beamforming and receive (Rx) time-division multiplexing(TDM).Theproposedfront-endASICis designed for driving a 64-channel one-dimensional transducer array in intracardiac echocardiography (ICE) ultrasound catheters. The ASIC is implemented in 60 V 0.18-μm HV-BCD technology, integrating Tx beam formers with high voltage pulsers and Rx front end in the same chip, which occupies 2.6 × 11 mm2 that can fit in the catheter size of 9 F (<3 mm). The proposed system reduces the number of wires from >64 to only 22 by integrating Tx beamformer that is programmable using a single low-voltage differential signaling data line. In Rx mode, the system uses 8:1 TDM with direct digital demultiplexing providing raw channel data that enables dynamic Rx beamforming using individual array elements. This system has been successfully used for B-mode imaging on standard ultrasound phantom with 401 mW of average power consumption. The ASIC has a compact element pitch-matched layout, which is also compatible with capacitive micromachined ultrasound transducer on CMOS application. This system addresses cable number and dimensional restrictions in catheters to enable ICE imaging under magnetic resonance imaging by reducing radio frequency induced heating.

-In ultrasound imaging catheter applications, gathering the data from multi-element transducer arrays is difficult as there is a restriction on cable count due to the diameter of the catheter. In such applications, CMUT-on-CMOS technology allows for 2D arrays with many elements to be designed and bonded directly onto CMOS circuitry. This allows for complex electronics to be placed at the tip of the catheter which leads to the possibility to include electronic multiplexing techniques to greatly reduce the cable count required for a large element array. Current approaches to cable reduction tend to rely on area and power hungry circuits to function, making them unsuitable for use in catheters. Furthermore the length requirement for catheters and lack of power available to on-chip cable drivers leads to limited signal strength at the receiver end. In this paper an alternative approach using Analogue Time Division Multiplexing (TDM) is presented, which addresses the cable restrictions of the catheter and, using a novel digital demultiplexing technique, allows for a reduction in the number of analogue signal processing stages required.

Capacitive Micromachined Ultrasonic Transducers (CMUTs) operating in immersion support dispersive evanescent waves due to the subwavelength periodic structure of electrostatically actuated membranes in the array. Evanescent wave characteristics also depend on the membrane resonance which is modified by the externally applied bias voltage, offering a mechanism to tune the CMUT array as an acoustic metamaterial. The dispersion and tunability characteristics are examined using a computationally efficient, mutual radiation impedance based approach to model a finite-size array and realistic parameters of variation. The simulations are verified, and tunability is demonstrated by experiments on a linear CMUT array operating in 2-12 MHz range.