PZT Probes Research Articles

Quantitative comparison of PZT and CMUT probes for photoacoustic imaging: Experimental validation

Photoacoustic (PA) signals are short ultrasound (US) pulses typically characterized by a single-cycle shape, often referred to as N-shape. The spectral content of such wideband signals ranges from a few hundred kilohertz to several tens of megahertz. Typical reception frequency responses of classical piezoelectric US imaging transducers, based on PZT technology, are not sufficiently broadband to fully preserve the entire information contained in PA signals, which are then filtered, thus limiting PA imaging performance. Capacitive micromachined ultrasonic transducers (CMUT) are rapidly emerging as a valid alternative to conventional PZT transducers in several medical ultrasound imaging applications. As compared to PZT transducers, CMUTs exhibit both higher sensitivity and significantly broader frequency response in reception, making their use attractive in PA imaging applications. This paper explores the advantages of the CMUT larger bandwidth in PA imaging by carrying out an experimental comparative study using various CMUT and PZT probes from different research laboratories and manufacturers. PA acquisitions are performed on a suture wire and on several home-made bimodal phantoms with both PZT and CMUT probes. Three criteria, based on the evaluation of pure receive impulse response, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) respectively, have been used for a quantitative comparison of imaging results. The measured fractional bandwidths of the CMUT arrays are larger compared to PZT probes. Moreover, both SNR and CNR are enhanced by at least 6dB with CMUT technology. This work highlights the potential of CMUT technology for PA imaging through qualitative and quantitative parameters.

Low frequency cMUT technology: Application to measurement of brain movement and assessment of bone quality

Following recent advances in medical ultrasound imaging methods almost all human tissues can currently be examined. There are, however, two exceptions: the human skeleton and the brain, because bone tissue is a strongly attenuating and defocusing medium, rendering classical pulse-echo imaging methods inappropriate. Specific imaging approaches within low frequency bands, i.e. 200kHz–2MHz, have therefore recently been developed and the results are very promising: (1) the technique for the bone is axial transmission measurement, which consists of using elastic guided modes to characterize all elastic constants of the medium; (2) for brain exploration, it has been demonstrated that brain movement can be measured (i.e. brain pulsatility) with elastography techniques. However, there are certain limitations in the fabrication of low frequency probes with classical technology, which involve finding an alternative to the traditional PZT. Capacitive Micromachined Ultrasonic Transducers (cMUTs) can overcome these limitations and greatly improve these new imaging modalities. The study presented here represents technological development with several goals: (1) the design and fabrication of two different low frequency linear arrays for bone and brain exploration, respectively the testing of axial transmission measurements with a cMUT probe and; (2) comparison with a PZT probe; (3) the development of an imaging method based on the elastography of brain pulsatility, its implementation in a commercial ultrasound scanner and clinical trials for the validation. The results obtained with cMUT and PZT probes are compared.

Large Area MEMS Based Ultrasound Device for Cancer Detection.

We present image results obtained using a prototype ultrasound array which demonstrates the fundamental architecture for a large area MEMS based ultrasound device for detection of breast cancer. The prototype array consists of a tiling of capacitive Micro-Machined Ultrasound Transducers (cMUTs) which have been flip-chip attached to a rigid organic substrate. The pitch on the cMUT elements is 185 um and the operating frequency is nominally 9 MHz. The spatial resolution of the new probe is comparable to production PZT probes, however the sensitivity is reduced by conditions that should be correctable. Simulated opposed-view image registration and Speed of Sound volume reconstruction results for ultrasound in the mammographic geometry are also presented.

An Improved Phased Array Ultrasonic Probe Using 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 Single Crystal

A 96-channel phased array probe for echocardiography using a single-plate, 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PZNT 91/9) single-crystal transducer with dimensions of 14×20 mm has been fabricated to realize greater sensitivity and broader bandwidth properties. The center frequency of the probe, 3.5 MHz, was selected to cover the bandwidths of two conventional lead zirconate titanate (PZT) ceramic probes with center frequencies of 2.5 and 3.75 MHz. A solder paste was used to connect a flexible printed circuit to the PZNT 91/9 transducer. The echo amplitude of the PZNT 91/9 probe is about 6 dB higher than that of the two PZT probes, and the fractional bandwidths are 30 and 25 percentage points wider, respectively. The B-mode image quality of the PZNT 91/9 probe is comparable to that of the two PZT probes, and the Doppler sensitivity of the PZNT 91/9 probe is almost equal to that of the 2.5 MHz PZT probe, which means that the PZNT 91/9 probe matches both the penetration of the 2.5 MHz PZT probe and the resolution of 3.75 MHz PZT probe.

Forty-channel phased array ultrasonic probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ single crystal

A 0.91Pb(Zn(1/3)Nb(2/3))O(3)-0.09PbTiO (3) (PZN-PT) single crystal with high electromechanical coupling factor (k(33))>90% has been used to fabricate a 40-channel phased array ultrasonic probe with greater sensitivity and broader bandwidth than conventional probes. This probe has a center frequency of 3.5 MHz and an aperture of about 6.0x7.5 mm. The standard probe fabrication process was modified for PZN-PT. The dispersion of echo signals was within +/-20% of the mean value. After recovery poling, the echo amplitude of the PZN-PT single-crystal probe is 8 and 5 dB higher than that of one- and two-matching-layer PZT probes, respectively. Moreover, the fractional bandwidth of the single-matching-layer PZN-PT probe is broader than that of the two-matching-layer PZT probes. The PZN-PT single crystals provide great improvements in the sensitivity and bandwidth of phased array probes.

Simulation and Fabrication Process for a Medical Phased Array Ultrasonic Probe using a 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 Single Crystal

Medical array ultrasonic probes using a 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (PZN-PT) single crystal exhibiting a high electromechanical coupling factor (k33) >90% have been studied in order to realize both a higher sensitivity and broader bandwidth properties. Pulse echo characteristics of the array probes, each transducer of which has dimensions of 6.0 mm×0.14 mm with a center frequency of 3.5 MHz, are simulated using the dielectric and the piezoelectric constants of the grown PZN-PT single crystals. Simulated echo amplitudes of the PZN-PT probes have been improved by as much as 7 dB compared with those of the conventional Pb(Zr1-x,Tix)O3 (PZT) ceramic ones. Moreover, the bandwidth of the PZN-PT probe is expected to be about 25% broader than those of the conventional PZT probes. It has been shown by simulation that the low acoustic impedance as well as the high coupling factor of the PZN-PT crystal contribute in broadening the bandwidth of the probe. The fabrication process of the array probe was investigated. A conventional method in which the dicing conditions are optimized and a novel dicing process are proposed.

Laser-generation of directional surface acoustic wave pulses in metals

A technique is presented for the generation of directional beams of ultrasonic Rayleigh waves in metals. A pulsed thermoelastic line-source of Rayleigh waves is produced by line-focusing Q-switched Nd: YAG laser pulses onto metal surfaces with a cylindrical lens. Ultrasonic frequency components of the resultant Rayleigh waves, detected by resonant PZT probes, are shown to be emitted preferentially broadside from the line-source in narrow beams. The directional characteristics of the beams are presented. Corresponding theoretical expressions are developed to describe the directivity pattern, and are found to be in good agreement with experimental results.