Hybrid multi/single layer array transducers for increased signal-to-noise ratio

Abstract

In medical ultrasound imaging, two-dimensional (2-D) array transducers are necessary to implement dynamic focusing in two dimensions, phase correction in two dimensions and high speed volumetric imaging. However, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance, which decreases the transducer signal-to-noise ratio (SNR). We have previously shown that SNR is improved using transducers made from multi-layer PZT, due to their lower electrical impedance. In this work, we hypothesize that SNR is further increased using a hybrid array configuration: in the transmit mode, a 10 Omega electronic transmitter excites a 10 Omega multi-layer array element; in the receive mode, a single layer element drives a high impedance preamplifier located in the transducer handle. The preamplifier drives the coaxial cable connected to the ultrasound scanner. For comparison, the following control configuration was used: in the transmit mode, a 50 Omega source excites a single layer element, and in the receive mode, a single layer element drives a coaxial cable load. For a 5x102 hybrid array operating at 7.5 MHz, maximum transmit output power was obtained with 9 PZT layers according to the KLM transmission line model. In this case, the simulated pulse-echo SNR was improved by 23.7 dB for the hybrid configuration compared to the control. With such dramatic improvement in pulse-echo SNR, low voltage transmitters can be used. These can be fabricated on integrated circuits and incorporated into the transducer handle.

Fabrication and Characterization of a Miniaturized 15-MHz Side-Looking Phased-Array Transducer Catheter

“…To obtain an acceptable SNR in tissue, future versions of the catheter could include impedance transformers or active preamplifiers on each channel, which are commonly used to boost the signal above the noise floor of the system for small elements with high impedance [25]. The uniformity of the measured values of −6-dB center frequency, −6-dB fractional BW, and peak-to-peak sensitivity of all the array elements is shown in Fig.…”

Evolution of ultrasound transducers: 1.5 and 2D arrays

“…Also in these developmental studies computing power of modern systems is fundamental. On one hand, sophisticated softwares permit design of innovative transducers and simulates their functioning [5,6,7]; on the other hand, the 1.5-and 2D array complexity requires high computing power.…”

“…In these transducers many layers of piezoelectric ceramic are incorporated in a very thin thickness giving greater sensitivity both in transmission and reception, a wider bandwidth and increased signal-to-noise ratio (Table 1) [7]. The advantages of multislice probes will be carried in progression even on the most complex matrix transducers [6]. …”