Emile Noothout

A Prototype PZT Matrix Transducer With Low-Power Integrated Receive ASIC for 3-D Transesophageal Echocardiography

This paper presents the design, fabrication, and experimental evaluation of a prototype lead zirconium titanate (PZT) matrix transducer with an integrated receive ASIC, as a proof of concept for a miniature three-dimensional (3-D) transesophageal echocardiography (TEE) probe. It consists of an array of 9 × 12 piezoelectric elements mounted on the ASIC via an integration scheme that involves direct electrical connections between a bond-pad array on the ASIC and the transducer elements. The ASIC addresses the critical challenge of reducing cable count, and includes front-end amplifiers with adjustable gains and microbeamformer circuits that locally process and combine echo signals received by the elements of each 3 × 3 subarray. Thus, an order-of-magnitude reduction in the number of receive channels is achieved. Dedicated circuit techniques are employed to meet the strict space and power constraints of TEE probes. The ASIC has been fabricated in a standard 0.18-μm CMOS process and consumes only 0.44 mW/channel. The prototype has been acoustically characterized in a water tank. The ASIC allows the array to be presteered across ±37° while achieving an overall dynamic range of 77 dB. Both the measured characteristics of the individual transducer elements and the performance of the ASIC are in good agreement with expectations, demonstrating the effectiveness of the proposed techniques.

A Broadband Polyvinylidene Difluoride-Based Hydrophone with Integrated Readout Circuit for Intravascular Photoacoustic Imaging

Intravascular photoacoustic (IVPA) imaging can visualize the coronary atherosclerotic plaque composition on the basis of the optical absorption contrast. Most of the photoacoustic (PA) energy of human coronary plaque lipids was found to lie in the frequency band between 2 and 15 MHz requiring a very broadband transducer, especially if a combination with intravascular ultrasound is desired. We have developed a broadband polyvinylidene difluoride (PVDF) transducer (0.6 × 0.6 mm, 52 μm thick) with integrated electronics to match the low capacitance of such a small polyvinylidene difluoride element (<5 pF/mm(2)) with the high capacitive load of the long cable (∼100 pF/m). The new readout circuit provides an output voltage with a sensitivity of about 3.8 μV/Pa at 2.25 MHz. Its response is flat within 10 dB in the range 2 to 15 MHz. The root mean square (rms) output noise level is 259 μV over the entire bandwidth (1-20 MHz), resulting in a minimum detectable pressure of 30 Pa at 2.25 MHz.

Low-power receive electronics for a miniature real-time 3D ultrasound probe

Transesophageal echocardiography (TEE) involves the use of an ultrasound transducer mounted at the tip of an endoscope to make ultrasonic images of the human heart from the esophagus. In conventional TEE probes, each transducer element is wired-out by a micro-coaxial cable to an external imaging system. To obtain real-time three-dimensional images, however, a two-dimensional transducer array with more than 1000 elements is required. Direct wiring of so many elements through an endoscope is not feasible, so channel reduction should be performed locally. In this paper, we present an application-specific integrated circuit (ASIC) that includes low-noise amplifiers, programmable-gain amplifiers and micro-beamformer circuits that locally process and combine the signals received by sub-groups of the transducer array. Thus, an order-of-magnitude channel reduction is achieved. The acoustic characterization of the prototype ASIC with a co-integrated transducer array will be presented.

A front-end ASIC with receive sub-array beamforming integrated with a 32 × 32 PZT matrix transducer for 3-D transesophageal echocardiography

This paper presents a power- and area-efficient front-end ASIC that is directly integrated with an array of 32 × 32 piezoelectric transducer elements to enable the next-generation miniature ultrasound probes for real-time 3-D transesophageal echocardiography. The 6.1 × 6.1 mm2 ASIC, implemented in a low-voltage 0.18 μm CMOS process, effectively reduces the number of cables required in the probes narrow shaft by means of 96 sub-array beamformers, which have a compact element-matched layout and employ mismatch-scrambling to enhance the dynamic range. The ASIC consumes less than 230 mW while receiving and its functionality has been successfully demonstrated in a 3-D imaging experiment.

A front-end ASIC with high-voltage transmit switching and receive digitization for forward-looking intravascular ultrasound

This paper presents a front-end ASIC for forward-looking intravascular ultrasound (IVUS) imaging. The ASIC is intended to be mounted at the tip of a catheter and can interface a total of 80 piezo-electric transducer elements with an imaging systems using only 4 cables, thus significantly reducing the system complexity compared to the prior art. It is capable of switching high-voltage transmit pulses to 16 transmit elements, and capturing the resulting echo signals using 64 multiplexed receive elements. The ASIC digitizes the received signals locally, providing more robust communication than prior analog approaches. Measurements show that the ASIC effectively switches transmit pulses up to 30 V, and digitizes echo signals with a bandwidth of 16 MHz, while consuming only 10 mW. Acoustic measurements in combination with a prototype transducer array demonstrate pulse transmission and reception. Finally, a B-mode image of a needle phantom demonstrates the imaging capability.

Acoustic characterization of a miniature matrix transducer for pediatric 3D transesophageal echocardiography

This paper presents the design, fabrication and characterization of a miniature PZT-on-CMOS matrix transducer for real-time pediatric 3-dimensional (3D) transesophageal echocardiography (TEE). This 3D TEE probe consists of a 32 × 32 array of PZT elements integrated on top of an Application Specific Integrated Circuit (ASIC). We propose a partitioned transmit/receive array architecture wherein the 8 × 8 transmitter elements, located at the centre of the array, are directly wired out and the remaining receive elements are grouped into 96 sub-arrays of 3 × 3 elements. The echoes received by these sub-groups are locally processed by micro-beamformer circuits in the ASIC that allow pre-steering up to ±37°. The PZT-on-CMOS matrix transducer has been characterized acoustically and has a centre frequency of 5.8 MHz, -6 dB bandwidth of 67%, a transmit efficiency of 6 kPa/V at 30 mm, and a receive dynamic range of 85 dB with minimum and maximum detectable pressures of 5 Pa and 84 kPa respectively. The properties are very suitable for a miniature pediatric real-time 3D TEE probe.

Forward-looking IVUS transducer with front-end ASIC for 3D imaging

Forward-looking intravascular ultrasound (FL-IVUS) transducers are needed to image complex lesions in the coronary arteries, such as chronic total occlusions (CTOs). To achieve 2D and 3D FL-IVUS imaging, transducer arrays can be integrated at the tip of the catheter. However, connecting the elements is challenging due to the limited space available. In this work, we present a FL-IVUS matrix transducer consisting of 16 transmit and 64 receive elements, which are interfaced with an ASIC that requires only 4 micro-coaxial cables. The transducer performance was characterized by hydrophone measurements and FL imaging of three spherical reflectors.