Search

Ultrasound imaging is a well established technology for echocardiography on humans. For cardiac imaging in small animals whose hearts beat at a rate higher than 300 beats per minute, the spatial and temporal resolution of current clinical ultrasonic scanners are far from ideal and simply inadequate for such applications. In this research, a real-time high frequency ultrasound imaging system was developed with a frame rate higher than 80 frames per second (fps) for cardiac applications in small animals. The device has a mechanical sector scanner using magnetic drive mechanism to reduce moving parts and ensure longevity. A very lightweight (< 0.28 g) single element transducer was specially designed and constructed for this research to achieve a frame rate of at least 80 fps. The 30-50 MHz transducers swept through an arc at the end of a pendulum for imaging the heart of small animals. The imaging electronics consisted of a low noise pulser/receiver, a high-speed data acquisition board, and digital signal processing algorithms. In vivo results on mouse embryos showed that real time ultrasound imaging at frame rate exceeding 80 fps could demonstrate detailed depiction of cardiac function with a spatial resolution of around 50 microns, which allows researchers to fully examine and monitor small animal cardiac functions.

This paper discusses the design, fabrication and testing of a 35 MHz linear ultrasonic array. The array features monolithic piezoelectric elements diced out of TRS 600FGHD fine grain high-density ceramic. A lossy urethane doped with gas filled microspheres is used as a kerf-filler to dampen inter-element acoustic propagation and reduce pulse length. The array incorporates a slotted single matching layer made from an unloaded epoxy. This matching layer also contributes to the reduction of pulse length and an increase in sensitivity. Array elements are spaced by a 50 mm pitch and interconnected via a flexible circuit. An 85 (Omega) transmission line coaxial cable is used to electrically match the array elements to the 50 (Omega) system electronics. The final 64-element array design is based on experimental results obtained from several four-element prototype arrays. An average center frequency of 34 MHz with a -6 dB bandwidth of at least 45% is achieved with the final prototype array. The maximum combined electrical and acoustical cross-talk for nearest and next nearest elements is less than -29 dB. The average -40 dB pulse length is 105 ns. The simple design and satisfactory performance of this array make it suitable for large-scale production.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper discusses two fabrication procedures used to build LiNbO3 single element ultrasonic transducers with center frequencies in the 50-100 MHz range. Transducers of varying dimensions were built for an f-number range of 1.5- 3.0. A conductive quarter wavelength silver epoxy matching layer, and a conductive silver epoxy backing, were used in all designs. The desired focal depths were achieved by either casting an acoustic lens on the transducer face or press-focusing the piezoelectric into a spherical curvature. For lens-focusing transducers the lens material EPO-TEK 301 was modeled as a second matching layer. The pressed-focused transducer design utilized parylene as the second matching layer. For devices that required electrical impedance matching, a low impedance transmission line coaxial cable was used. All transducers were tested in a pulse-echo insertion loss arrangement, whereby the center frequency, bandwidth, insertion loss, and focal depth were measured. Several transducers were fabricated with center frequencies in the 50 to 100 MHz range. The measured -6dB bandwidths and two-way insertion loss values ranged from 33% to 70% and 12.5dB to 23.0dB, respectively. Both the lens-focusing and press-focusing techniques were successful in producing the desired focal depth without significantly compromising device sensitivity and bandwidth.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The design and fabrication of high frequency single element ultrasonic transducers present a multitude of challenges for the transducer engineer, from size constraints to electrical impedance matching. This paper discusses the trade-offs involved in a procedure used to fabricate transducers with center frequencies in the 25 MHz - 100 MHz range using 36 degree rotated Y-cut lithium niobate (LiNbO3) as the active element. Transducers of varying dimensions were built according to an f-number range of 2 - 3.5. A (lambda) /4 silver epoxy matching layer with an acoustic impedance of 7.3 Mrayls was used. Desired focal depths were achieved with use of an acoustic lens. Silver epoxy backing with an acoustic impedance of approximately 5.9 Mrayls was also used in all designs. All transducers were designed around a 50(Omega) send and receive circuit. Electrical tuning of the transducer to the receive circuitry was achieved by using an RF transformer. All transducers were tested in a pulse-echo arrangement using a Panametrics 5900PR pulser, a Wavetek function generator and a LeCroy digital oscilloscope. The bandwidth, insertion loss, and depth of focus were measured. Several transducers were fabricated with -6dB bandwidths ranging from 62% to 74%, and two-way insertion loss values ranging from -14dB to -22dB.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A wide variety of fabrication techniques and materials produce ultrasound transducers with very different performance characteristics. High frequency (50 MHz), focused single element transducers using lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO3) ceramic, polyvinylidene fluoride (PVDF) polymer and lithium niobate (LiNbO3) single crystal are compared in design and performance. The transducers were all constructed with a 3 mm aperture and f- number of 2 - 3. Design considerations discussed include optimization of designs using different lens, backing and matching materials for acoustic matching and the use of several electrical tuning techniques to match the transducers to the 50(Omega) circuitry. Transducers were tested for insertion loss and -6dB bandwidth using a quartz flat- plate target. Insertion loss measurements between transducers were -20dB to -50dB with bandwidths in the range of 50 - 120%. Through the use of an ultrasound backscatter microscope (UBM), the transducer were compared using in vitro images of the human eye. Images of a wire phantom were also made for comparison of lateral and axial resolution of each device.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.