Segmented Annular Array Research Articles

Sparse hand-held probe for optoacoustic ultrasound volumetric imaging: an experimental proof-of-concept study.

We present an experimental proof-of-concept study on the performance of a sparse segmented annular array for optoacoustic imaging. A capacitive micromachined ultrasonic transducer was equipped with a negatively focused acoustic lens and scanned in an annular fashion to exploit the performance of the sparse array geometry proposed in our recent numerical studies [Biomed. Opt. Express10, 1545 (2019)BOEICL2156-708510.1364/BOE.10.001545; J. Biomed. Opt.23, 025004 (2018)JBOPFO1083-366810.1117/1.JBO.23.2.025004]. A dedicated water tank was made using a 3D printer for light delivery and mounting the sample. A phantom experiment was carried out to showcase the possibility of full-field optoacoustic ultrasound (OPUS) imaging and confirm the earlier numerical results. This proof of concept opens the door towards a prototype of OPUS imaging for (pre-) clinical studies.

Sparse sampling and reconstruction for an optoacoustic ultrasound volumetric hand-held probe.

Accurate anatomical localization of functional information is the main goal of hybridizing optoacoustic and ultrasound imaging, with the promise of early stage diagnosis and disease pathophysiology. Optoacoustic integration to ultrasound is a relatively mature technique for clinical two-dimensional imaging, however the complexity of biological samples places particular demands for volumetric measurement and reconstruction. This integration is a multi-fold challenge that is mainly associated with the system geometry, the sampling and beam quality. In this study, we evaluated the design geometry for the sparse ultrasonic hand-held probe that is popularly associated with three-dimensional imaging of anatomical deformation, to incorporate the three-dimensional optoacoustic physiological information. We explored the imaging performance of three unconventional annular geometries; namely, segmented, spiral, and circular geometries. To avoid bias evaluation, two classes of analytical and model-based algorithms were used. The superior performance of the segmented annular array for recovery of the true object is demonstrated. Along with the model-based approach, this geometry offers spatial invariant resolution for the optoacoustic mode for the given field of view.The analytical approach, on the other hand, is computationally less expensive and is the method of choice for ultrasound imaging. Our design can potentially evolve into a valuable diagnostic tool, particularly for vascular-related disease.

TheSi28(p,t)Si26*(p) reaction and implications for the astrophysicalAl25(p,γ)Si26reaction rate

Several resonances in $^{25}\mathrm{Al}$($p,\ensuremath{\gamma}$)$^{26}\mathrm{Si}$ have been studied via the $^{28}\mathrm{Si}$($p,t$)$^{26}\mathrm{Si}$ reaction. Triton energies and angular distributions were measured using a segmented annular detector array. An additional silicon detector array was used to simultaneously detect the coincident protons emitted from the decay of states in $^{26}\mathrm{Si}$ above the proton threshold in order to determine branching ratios. A resonance at $5927\ifmmode\pm\else\textpm\fi{}4$ keV has been experimentally confirmed as the first $\ensuremath{\ell}=0$ state above the proton threshold, with a proton branching ratio consistent with one.

Beam Steering with Segmented Annular Arrays

Two-dimensional (2-D) arrays of squared matrix have maximum periodicity in their main directions; consequently, they require half wavelength (lambda/2), interelement spacing to avoid grating lobes. This condition gives rise to well-known problems derived from the huge number of array elements and from their small size. In contrast, 2-D arrays with curvilinear configuration produce lower grating lobes and, therefore, allow the element size to be increased beyond lambda/2. Using larger elements, these arrays have the advantage of reducing the number of elements and of increasing the signal-to-noise ratio (SNR). In this paper, the beamforming properties of segmented annular phased arrays are theoretically analyzed and compared with the equivalent squared matrix array. In the first part, point-like elements are considered in order to facilitate the field analysis with respect to the array structure. Afterward, the effect of the element size on the steered beam properties also is presented. In the examples, it is shown that the segmented annular array has notably lower grating lobes than the equivalent squared matrix array and that it is possible to design segmented annular arrays with interelement distance higher than lambda whose beam characteristics are perfectly valid for volumetric imaging applications.

A small 2D ultrasonic array for NDT applications

A prototype of two-dimensional transducer array with reduced number of elements, based on segmented annular distribution is presented. The capability of this array to produce volumetric imaging is compared to the equivalent conventional 2D squared matrix array. The comparison between both apertures is made for the cases of the full-array emission/reception mode and SAFT mode. From the analysis it is deduced that the segmented annular arrays produce lower grating lobes than squared arrays, improving the image contrast. The fabrication process of a segmented annular array of 64 elements and the experimental work made with this array transducer is also presented in this paper.

Development of a segmented annular array transducer for acoustic imaging

Abstract A 1.6 MHz segmented annular array transducer of 64 elements made from a piezoelectric composite as a monolithic support has been manufactured and characterised. Input electrical impedance and pulse response of each array element was in good agreement with the results calculated by using the KLM model. Cross-coupling between nearest neighbours was −45 dB at the resonance frequency assuring the good array performance in terms of cross-coupling and elements isolation. Vibration surface measurement of a sector of elements excited simultaneously was made. The transducer was designed for the inspection of solid materials in non-destructive testing (NDT).

A model to predict the transient radiation from segmented annular apertures radiating into solid media

An approach to predict the compressional wave transient radiation in solid load media from elements and arrays comprised of segmented annular apertures is described. The model may also be applied to the simulation of the transient radiation from circular, rectangular, and annular apertures by suitable parameter manipulation. The approach is based on the method developed by Stepanishen to model propagation in a fluid medium. A suitable angular weighting factor, that of Miller and Pursey, is included to account for the multimode nature of solids, A number of experimental results, including single-element and phased array operation, obtained from a prototype segmented annular array system are presented. These results demonstrate good agreement when compared with those obtained from the theoretical model.