A flexible annular-array imaging platform for micro-ultrasound.

Micro-ultrasound is an invaluable imaging tool for many clinical and preclinical applications requiring high resolution (approximately several tens of micrometers). Imaging systems for micro-ultrasound, including single-element imaging systems and linear-array imaging systems, have been developed extensively in recent years. Single-element systems are cheaper, but linear-array systems give much better image quality at a higher expense. Annular-array-based systems provide a third alternative, striking a balance between image quality and expense. This paper presents the development of a novel programmable and real-time annular-array imaging platform for micro-ultrasound. It supports multi-channel dynamic beamforming techniques for large-depth-of-field imaging. The major image processing algorithms were achieved by a novel field-programmable gate array technology for high speed and flexibility. Real-time imaging was achieved by fast processing algorithms and high-speed data transfer interface. The platform utilizes a printed circuit board scheme incorporating state-of-the-art electronics for compactness and cost effectiveness. Extensive tests including hardware, algorithms, wire phantom, and tissue mimicking phantom measurements were conducted to demonstrate good performance of the platform. The calculated contrast-to-noise ratio (CNR) of the tissue phantom measurements were higher than 1.2 in the range of 3.8 to 8.7 mm imaging depth. The platform supported more than 25 images per second for real-time image acquisition. The depth-of-field had about 2.5-fold improvement compared to single-element transducer imaging.

Thickness Dependent Characteristics of High Permittivity PMN-0.32PT Single Crystal for High Frequency Medical Imaging Applications.

The dielectric, piezoelectric, and acoustic properties of PMN-0.32PT (Pb(Mg(1/3)Nb(2/3)) O(3)-PbTiO(3)) single crystals were investigated as a function of sample thickness ranging from 120 to 30 µm in order to enlighten the origin of property degradation of crystals for high frequency ultrasound applications. Electromechanical coupling factor(k(t) ), clamped and free dielectric constants decreased but sound velocity increased with decreasing crystal thickness. Particularly, repoling of the PMN-PT crystals would bring about a noteworthy enhancement in electromechanical and dielectric properties, which urges the importance of PMN-PT as a promising piezoelectric material for high frequency ultrasound transducers.

A high-frequency annular-array transducer using an interdigital bonded 1-3 composite.

This paper reports the design, fabrication, and characterization of a 1-3 composite annular-array transducer. An interdigital bonded (IB) 1-3 composite was prepared using two IB operations on a fine-grain piezoelectric ceramic. The final composite had 19-µm-wide posts separated by 6-µm-wide polymer kerfs. A novel method to remove metal electrodes from polymer portions of the 1-3 composite was established to eliminate the need for patterning and aligning the electrode on the composite to the electrodes on a flexible circuit. Unloaded epoxy was used for both the matching and backing layers and a flexible circuit was used for interconnect. A prototype array was successfully fabricated and tested. The results were in reasonable agreement with those predicted by a circuit-analogous model. The average center frequency estimated from the measured pulse-echo responses of array elements was 33.5 MHz and the -6-dB fractional bandwidth was 57%. The average insertion loss recorded was 14.3 dB, and the maximum crosstalk between the nearest-neighbor elements was less than -37 dB. Images of a wire phantom and excised porcine eye were obtained to show the capabilities of the array for high-frequency ultrasound imaging.