Time-division multiplexing for cable reduction in ultrasound imaging catheters

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

Direct Digital Demultiplexing of Analog TDM Signals for Cable Reduction in Ultrasound Imaging Catheters.

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

Front-end electronics for cable reduction in Intracardiac Echocardiography (ICE) catheters

3-D imaging ICE catheters with large element counts present design challenges in achieving simultaneous data readout from all elements while significantly reducing cable count for a small catheter diameter. Current approaches such as microbeamformer techniques tend to rely on area and power hungry circuits, making them undesirable for ICE catheters. In this paper, a system which uses are an efficient real-time programmable on-chip transmit (TX) beamformer circuitry to reduce the cable count on the TX side and analog 8/1 Time Division Multiplexing (TDM) with Direct Digital Demodulation (DDD) to reduce the cable count on the receive (RX) side is presented

Real-Time Imaging System using a 12-MHz Forward-Looking Catheter with Single Chip CMUT-on-CMOS Array

Forward looking (FL) imaging catheters would be an important tool for several intravascular ultrasound (IVUS) and intracardiac echocardiography (ICE) applications. Single chip capacitive micromachined ultrasonic transducer (CMUT) arrays fabricated on front-end CMOS electronics with simplified electrical interconnect have been previously developed for highly flexible and compact catheters. In this study, we present a custom built real time imaging system utilizing catheters with single chip CMUT-on-CMOS arrays and show initial imaging results. The fabricated array has a dual-ring structure with 64 transmit (Tx) and 56 receive (Rx) elements. The CMUT arrays fit on a 2.1 mm diameter circular region with all the required front-end electronics. The device operates at 12 MHz center frequency and has around 20 V collapse voltage. The single-chip system requires 13 external connections including 4 Rx channels and power lines. The electrical connections to micro cables in the catheter are made from the top side of the chip using polyimide flex tapes. The device is placed on a 6-Fr catheter shaft and secured with a medical grade silicon rubber. For real time data acquisition, we developed a custom design FPGA based imaging platform to generate digital control sequences for the chip and collect RF data from Rx outputs. We performed imaging experiments using wire phantoms immersed in water to test the real time imaging system. The system has the potential to generate images at 32 fps rate with the particular catheter. The overall system is fully functional and shows promising image performance

Single-Chip Reduced-Wire CMUT-on-CMOS System for Intracardiac Echocardiography

CMUT-on-CMOS integration is particularly suitable for catheter based ultrasound imaging applications, where electronics integration enables multiplexing capabilities to reduce the number of electrical connections leading to smaller catheter cable profiles. Here, a single-chip CMUT-on-CMOS system for intracardiac echocardiography (ICE) is presented. In this system, a 64 element 1-D CMUT array is fabricated over an application specific integrated circuit (ASIC) that features a programmable transmit beamformer with high voltage (HV) pulsers and receive circuits using 8:1 time division multiplexing (TDM). Integration of pitch matched 64 channel front-end circuits with CMUT arrays in a single-chip configuration allows for implementation of catheter probes with miniaturization, reduced number of cables, and better mechanical flexibility. The ASIC is implemented in 60 V 0.18 μm HV process. It occupies 2.6×11 mm 2 which can fit in the catheter size of 9F, and reduces the number of wires from more than 64 to 22. This system is used for B-mode imaging of imaging phantoms and its potential application for 2D CMUT-on-CMOS arrays is discussed

Single-Chip Reduced-Wire Active Catheter System with Programmable Transmit Beamforming and Receive Time-Division Multiplexing for Intracardiac Echocardiography

Intracardiac echocardiography (ICE) provides real-time ultrasound imaging of the heart anatomy from inside, guiding interventions like valve repair, closure of atrial septal defects (ASD) and catheter-based ablation to treat atrial fibrillation. With its better image quality and ease of use, ICE is becoming the preferred imaging modality over transesophageal echography (TEE) for structural heart interventions. The existing commercial ICE catheters, however, offer a limited 2-D or 3-D field of view despite catheters utilizing large number of wires. In these catheters, each element in the ICE array is connected to the backend data-acquisition channel with a separate wire, which is a critical barrier for improving image quality and widening the field of view. In order to use ICE catheters under MRI instead of the ionizing X-ray radiation-based angiography, the number of interconnect wires in the catheter should be minimized to reduce RF-induced heating. Furthermore, reducing the number of wires improves the flexibility and lowers the cost of the single-use ICE catheters

Hepatitis B and Renal Disease

Glomerulonephritis is an important extrahepatic manifestation of chronic hepatitis B virus (HBV) infection. The uncommon occurrence, variability in renal histopathology, and heterogeneity in clinical course present challenges in clinical studies and have resulted in a relative paucity of data and uncertainty with regard to the optimal management of HBV-related glomerular diseases. The advent of nucleos(t)ide analogue medications that effectively suppress HBV replication has markedly altered the clinical outcomes of kidney transplant recipients with HBV infection, but the emergence of drug resistance is an escalating problem. This article reviews the recent knowledge of the pathogenesis and treatment of HBV-related membranous nephropathy, and discusses the management of hepatitis B in kidney transplant recipients, which is continuously evolving

Supply-Inverted Bipolar Pulser and Tx/Rx Switch for CMUTs Above the Process Limit for High Pressure Pulse Generation

A combined supply-inverted bipolar pulser and a Tx/Rx switch is proposed to drive capacitive micromachined ultrasonic transducers (CMUTs). The supply-inverted bipolar pulser adopts a bootstrap circuit combined with stacked transistors, which guarantees high voltage (HV) operation above the process limit without lowering device reliability. This circuit generates an output signal with a peak-to-peak voltage that is almost twice the supply level. It generates a bipolar pulse with only positive supply voltages. The Tx/Rx switch adopts a diode-bridge structure with the protection scheme dedicated to this proposed pulser. A proof- of-concept ASIC prototype has been implemented in 0.18-μ m HV CMOS/DMOS technology with 60 V devices. Measurement results show that the proposed pulser can safely generate a bipolar pulse of -34.6 to 45 V, from a single 45 V supply voltage. The Tx/Rx switch blocks the HV bipolar pulse, resulting in less than 1.6 V at the input of the receiver. Acoustic measurements are performed connecting the pulser to CMUTs with 2 pF capacitance and 8 MHz center frequency. The variation of acoustic output pressures for different pulse shapes were simulated with the large signal CMUT model and compared with the experimental results for transmit pressure optimization. A potential implementation of the methods using MEMS fabrication methods is also described