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 (λ/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 λ/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 λ whose beam characteristics are perfectly valid for volumetric imaging applications.This paper received the support of the Education and Science Ministry of Spain under its DPI2002-01583, DPI2004-06470, and DPI2004-06756 projects.Peer reviewe

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 (λ/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 λ/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 λ whose beam characteristics are perfectly valid for volumetric imaging applications.This paper received the support of the Education and Science Ministry of Spain under its DPI2002-01583, DPI2004-06470, and DPI2004-06756 projects.Peer reviewe

2D array design based on Fermat spiral for ultrasound imaging

10 páginas, 10 figuras, 3 tablas.-- PACS classification codes: 87.57.−s; 87.63.dh; 43.60.Fg; 43.38.Hz; 43.35.Zc.-- El PDF del artículo es la versión pre-print.The main challenge faced by 3D ultrasonic imaging with 2D array transducers is the large number of elements required to achieve an acceptable level of quality in the images. Therefore, the optimisation of the array layout, in order to reduce the number of active elements in the aperture, has been a research topic in the last years. Nowadays, array technology has made viable the production of 2D arrays with larger flexibility on elements size, shape and position, allowing to study other configurations different to the classical matrix organisation, such as circular, archimedes spiral or polygonal layout between others. In this work, the problem of designing an imaging system array with large apertures and a very limited number of active elements (Ne=128 and Ne=256) using the Fermat spiral layout has been studied. As summary, a general discussion about the most interesting cases is presented.This work was supported in part by the Spanish Ministry of Education and Science under grant BES-2005-7704 and the projects DPI2007-65408-C02-01 and TRA2007-67711/AUT.N

A Computational Method to Calculate the Longitudinal Wave Evolution Caused by Interfaces Between Isotropic Media

This paper presents a computational method to calculate the reflected and transmitted ultrasonic fields at interfaces of complex geometry. The method is performed in two steps. As first step, the velocity potential impulse response from an arbitrary aperture is determined at the interface using the Rayleigh integral and considering the reflection and transmission coefficients. In a second step, the simulated fields are calculated by applying the Rayleigh-Sommerfeld integral to the whole, extended interface. In order to validate the method, some experimental cases as, for instance, plane and cylindrical concave surfaces between two media (water-acrylic) were tested. The experimental ultrasonic fields are in good agreement with those provided by the model. Furthermore, in the work, the compromise between the accuracy of the method and the computation time is studied.The authors would like to thank the National Council for Scientific and Technological Development (CNPq), Brazil, for the postdoctoral scholarship to Flávio Buiochi in the development of this work and to the Comunidad Autónoma de Madrid (CAM) and Comisión Europea (CE) for the postdoctoral grant to Oscar Martínez. The sup- ports from Comisión Interministerial de Ciencia y Tecnología (CICYT) DPI2001-2156-C02-02, DPI-2001-2043 and Advanced Array Technologies for Optimised Maintenance and Inspection in Critical Applications (AMICA)GRD1-CT2000-00322 EU projects are also acknowledged.Peer reviewe

Improving synthetic aperture image by image compounding in beamforming process

In this work, signal processing techniques are used to improve the quality of image based on multi-element synthetic aperture techniques. Using several apodization functions to obtain different side lobes distribution, a polarity function and a threshold criterium are used to develop an image compounding technique. The spatial diversity is increased using an additional array, which generates complementary information about the defects, improving the results of the proposed algorithm and producing high resolution and contrast images. The inspection of isotropic plate-like structures using linear arrays and Lamb waves is presented. Experimental results are shown for a 1-mm-thick isotropic aluminum plate with artificial defects using linear arrays formed by 30 piezoelectric elements, with the low dispersion symmetric mode S0 at the frequency of 330 kHz. © 2011 American Institute of Physics

Revealing cell populations catching the early stages of human embryo development in naive pluripotent stem cell cultures

Naive human pluripotent stem cells (hPSCs) are defined as the in vitro counterpart of the human preimplantation embryo's epiblast and are used as a model system to study developmental processes. In this study, we report the discovery and characterization of distinct cell populations coexisting with epiblast-like cells in 5iLAF naive human induced PSC (hiPSC) cultures. It is noteworthy that these populations closely resemble different cell types of the human embryo at early developmental stages. While epiblast-like cells represent the main cell population, interestingly we detect a cell population with gene and transposable element expression profile closely resembling the totipotent eight-cell (8C)-stage human embryo, and three cell populations analogous to trophectoderm cells at different stages of their maturation process: transition, early, and mature stages. Moreover, we reveal the presence of cells resembling primitive endoderm. Thus, 5iLAF naive hiPSC cultures provide an excellent opportunity to model the earliest events of human embryogenesis, from the 8C stage to the peri-implantation period

Loss of the matrix metalloproteinase-10 causes premature features of aging in satellite cells

Aged muscles accumulate satellite cells with a striking decline response to damage. Although intrinsic defects in satellite cells themselves are the major contributors to aging-associated stem cell dysfunction, increasing evidence suggests that changes in the muscle-stem cell local microenvironment also contribute to aging. Here, we demonstrate that loss of the matrix metalloproteinase-10 (MMP-10) in young mice alters the composition of the muscle extracellular matrix (ECM), and specifically disrupts the extracellular matrix of the satellite cell niche. This situation causes premature features of aging in the satellite cells, contributing to their functional decline and a predisposition to enter senescence under proliferative pressure. Similarly, reduction of MMP-10 levels in young satellite cells from wild type animals induces a senescence response, while addition of the protease delays this program. Significantly, the effect of MMP-10 on satellite cell aging can be extended to another context of muscle wasting, muscular dystrophy. Systemic treatment of mdx dystrophic mice with MMP-10 prevents the muscle deterioration phenotype and reduces cellular damage in the satellite cells, which are normally under replicative pressure. Most importantly, MMP-10 conserves its protective effect in the satellite cell-derived myoblasts isolated from a Duchenne muscular dystrophy patient by decreasing the accumulation of damaged DNA. Hence, MMP-10 provides a previously unrecognized therapeutic opportunity to delay satellite cell aging and overcome satellite cell dysfunction in dystrophic muscles

La \uabmetaf\uedsica de la experiencia interior\ubb clave teor\ue9tica de la estructura relacional de la persona.

Riflessione sull'esperienza interiore come esperienza metafisica della relazionalit\ue0 accessibile all'essere uman