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1.
Malar J ; 20(1): 88, 2021 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-33579285

RESUMO

BACKGROUND: Malaria remains a serious health threat in the Amazonas Region of Peru and approximately 95% of the cases, mainly Plasmodium vivax, are found in native communities of The Rio Santiago District, Condorcanqui Province. In 2019, more than one thousand malaria cases were reported, with an unusual number of Plasmodium falciparum autochthonous cases. The present study aims to report this P. falciparum outbreak while describing the epidemiology of malaria and the risk factors associated in the native communities of Amazonas, Peru. METHODS: The DIRESA-Amazonas in collaboration with the Condorcanqui Health Network and the Institute of Tropical Diseases of the UNTRM carried out a malaria Active Case Detection (ACD III) between January 31st and February 10th of 2020. A total of 2718 (47.4%) individuals from 21 native communities grouped in eight sanitary districts, were screened for malaria infections. Each participant was screened for malaria using microscopy. Follow-up surveys were conducted for all malaria positive individuals to collect socio-demographic data. Spatial clustering of infection risk was calculated using a generalized linear model (GLM). Analysis of risk considered factors such as gender, age, type of infection, symptomatology, and parasitaemia. RESULTS: The study suggests that the P. falciparum index case was imported from Loreto and later spread to other communities of Rio Santiago during 2019. The ACD III reported 220 (8.1%) malaria cases, 46 P. falciparum, 168 P. vivax and 6 mixed infections. SaTScan analysis detected a cluster of high infection risk in Middle Rio Santiago and a particular high P. falciparum infection risk cluster in Upper Rio Santiago. Interestingly, the evaluation of different risk factors showed significant associations between low parasitaemia and P. falciparum asymptomatic cases. CONCLUSION: This is the first report of a P. falciparum outbreak in native communities of Condorcanqui, Amazonas. Timely identification and treatment of symptomatic and asymptomatic cases are critical to achieve malaria control and possible elimination in this area. However, the current malaria situation in Condorcanqui is uncertain, given that malaria ACD activities have been postponed due to COVID-19.


Assuntos
Surtos de Doenças , Malária Falciparum/epidemiologia , Adolescente , Adulto , Criança , Pré-Escolar , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Peru/epidemiologia , População Rural , Adulto Jovem
2.
Skin Res Technol ; 25(6): 881-889, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31400033

RESUMO

BACKGROUND AND OBJECTIVE: Different biological models have shown how mechanical stimulation may induce physiological responses from solicited cells, tissues, or organs. In models of cultured skin cells, the frequency of the mechanical stress appears to be a paramount parameter, generating a biological response in some cells, particularly from dermal fibroblasts. Our objective was to explore in ex vivo human skin explants the effects of mechanical stimulation. MATERIALS AND METHODS: Mechanical stimulations were provided by a torque test device, with different end effectors, able to generate cyclic strains at different frequencies (from 40 to 120 Hz). Skin explant samples were stimulated twice daily by the device for one minute, over 10 days. RESULTS: At days 0, 5, and 10, samples were processed by immunohistological procedures, allowing some structural dermal proteins to be quantified (fluorescence). As compared to untreated skin explant samples, the stimulation procedure clearly led some proteins of the dermal-epidermal and some dermal proteins to be overexpressed. This stimulation was found to be frequency-dependent, with the greatest overall increases occurring at 60 and 90 Hz. CONCLUSION: For the first time, ultrafast ultrasound imaging in vitro (phantom mimicking skin mechanical properties) was used to analyze mechanical waves transmitted to the skin layers as a function of end effector shape.


Assuntos
Fenômenos Biomecânicos/fisiologia , Estimulação Física , Fenômenos Fisiológicos da Pele , Vibração , Adulto , Idoso , Envelhecimento/fisiologia , Feminino , Humanos , Pessoa de Meia-Idade , Modelos Biológicos , Imagens de Fantasmas , Pele/diagnóstico por imagem , Ultrassonografia
3.
Angew Chem Int Ed Engl ; 58(24): 8221-8225, 2019 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-30974013

RESUMO

The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well-defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution-phase precursor entities are then reduced electrochemically-one by one-to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4 -filled micelles. These Au NP-decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor-filled nanocontainers are presented as a new route to nanoparticle-modified electrodes with high catalyst utilization.

4.
Glia ; 64(12): 2306-2320, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-27687291

RESUMO

Fetal growth restriction (FGR) is a major complication of human pregnancy, frequently resulting from placental vascular diseases and prenatal malnutrition, and is associated with adverse neurocognitive outcomes throughout life. However, the mechanisms linking poor fetal growth and neurocognitive impairment are unclear. Here, we aimed to correlate changes in gene expression induced by FGR in rats and abnormal cerebral white matter maturation, brain microstructure, and cortical connectivity in vivo. We investigated a model of FGR induced by low-protein-diet malnutrition between embryonic day 0 and birth using an interdisciplinary approach combining advanced brain imaging, in vivo connectivity, microarray analysis of sorted oligodendroglial and microglial cells and histology. We show that myelination and brain function are both significantly altered in our model of FGR. These alterations, detected first in the white matter on magnetic resonance imaging significantly reduced cortical connectivity as assessed by ultrafast ultrasound imaging. Fetal growth retardation was found associated with white matter dysmaturation as shown by the immunohistochemical profiles and microarrays analyses. Strikingly, transcriptomic and gene network analyses reveal not only a myelination deficit in growth-restricted pups, but also the extensive deregulation of genes controlling neuroinflammation and the cell cycle in both oligodendrocytes and microglia. Our findings shed new light on the cellular and gene regulatory mechanisms mediating brain structural and functional defects in malnutrition-induced FGR, and suggest, for the first time, a neuroinflammatory basis for the poor neurocognitive outcome observed in growth-restricted human infants. GLIA 2016;64:2306-2320.


Assuntos
Lesões Encefálicas/etiologia , Lesões Encefálicas/patologia , Retardo do Crescimento Fetal/fisiopatologia , Microglia/metabolismo , Oligodendroglia/metabolismo , Transcriptoma/fisiologia , Proteína da Polipose Adenomatosa do Colo/metabolismo , Animais , Animais Recém-Nascidos , Antígenos/metabolismo , Antígenos CD/metabolismo , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Lesões Encefálicas/diagnóstico por imagem , Citocinas/metabolismo , Feminino , Expressão Gênica/fisiologia , Lipopolissacarídeos/farmacologia , Proteína Básica da Mielina/metabolismo , Vias Neurais/diagnóstico por imagem , Vias Neurais/efeitos dos fármacos , Fator de Transcrição 2 de Oligodendrócitos/metabolismo , Gravidez , Proteoglicanas/metabolismo , Ratos , Ratos Sprague-Dawley
5.
J Acoust Soc Am ; 138(4): 2499-507, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26520332

RESUMO

Evaluation of tissue engineering constructs is performed by a series of different tests. In many cases it is important to match the mechanical properties of these constructs to those of native tissues. However, many mechanical testing methods are destructive in nature which increases cost for evaluation because of the need for additional samples reserved for these assessments. A wave propagation method is proposed for characterizing the shear elasticity of thin layers bounded by a rigid substrate and fluid-loading, similar to the configuration for many tissue engineering applications. An analytic wave propagation model was derived for this configuration and compared against finite element model simulations and numerical solutions from the software package Disperse. The results from the different models found very good agreement. Experiments were performed in tissue-mimicking gelatin phantoms with thicknesses of 1 and 4 mm and found that the wave propagation method could resolve the shear modulus with very good accuracy, no more than 4.10% error. This method could be used in tissue engineering applications to monitor tissue engineering construct maturation with a nondestructive wave propagation method to evaluate the shear modulus of a material.


Assuntos
Imagens de Fantasmas , Engenharia Tecidual/métodos , Ondas Ultrassônicas , Simulação por Computador , Elasticidade , Análise de Elementos Finitos , Gelatina , Glicerol , Modelos Teóricos , Resistência ao Cisalhamento , Software
6.
ISA Trans ; 143: 94-102, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37852847

RESUMO

This paper is concerned with fault reconstruction based on sliding mode observers; its contribution is twofold: on the one hand, it develops a novel sliding mode observer whose nominal system is nonlinear, thus relaxing former limitations on the subject, namely, rank restrictions, linear outputs, and conservative bounds; on the other hand, based on the referred sliding mode observer, a novel robust fault reconstruction scheme is constructed which can solve a variety of problems that former methodologies cannot treat. Nonlinearities are cast as convex expressions, which enables obtaining design conditions in the form of linear matrix inequalities. Examples are provided to compare the proposal with former methodologies, thus highlighting the contributions.

7.
J Acoust Soc Am ; 129(3): 1344-54, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21428498

RESUMO

Arterial elasticity has been proposed as an independent predictor of cardiovascular diseases and mortality. Identification of the different propagating modes in thin shells can be used to characterize the elastic properties. Ultrasound radiation force was used to generate local mechanical waves in the wall of a urethane tube or an excised pig carotid artery. The waves were tracked using pulse-echo ultrasound. A modal analysis using two-dimensional discrete fast Fourier transform was performed on the time-space signal. This allowed the visualization of different modes of propagation and characterization of dispersion curves for both structures. The urethane tube/artery was mounted in a metallic frame, embedded in tissue-mimicking gelatin, cannulated, and pressurized over a range of 10-100 mmHg. The k-space and the dispersion curves of the urethane tube showed one mode of propagation, with no effect of transmural pressure. Fitting of a Lamb wave model estimated Young's modulus in the urethane tube around 560 kPa. Young's modulus of the artery ranged from 72 to 134 kPa at 10 and 100 mmHg, respectively. The changes observed in the artery dispersion curves suggest that this methodology of exciting mechanical waves and characterizing the modes of propagation has potential for studying arterial elasticity.


Assuntos
Artérias Carótidas/diagnóstico por imagem , Técnicas de Imagem por Elasticidade/métodos , Interpretação de Imagem Assistida por Computador , Animais , Pressão Sanguínea , Complacência (Medida de Distensibilidade) , Módulo de Elasticidade , Técnicas de Imagem por Elasticidade/instrumentação , Análise de Fourier , Gelatina , Modelos Cardiovasculares , Imagens de Fantasmas , Fluxo Pulsátil , Suínos , Fatores de Tempo , Uretana
8.
J Acoust Soc Am ; 130(6): 3549-52, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22225009

RESUMO

In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented.


Assuntos
Elasticidade/fisiologia , Modelos Biológicos , Ultrassom , Artérias/fisiologia , Coração/fisiologia , Imagens de Fantasmas , Resistência ao Cisalhamento/fisiologia , Viscosidade
9.
Phys Med Biol ; 66(5)2021 02 26.
Artigo em Inglês | MEDLINE | ID: mdl-33361564

RESUMO

Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases withRe. Moreover, from the FTLE field we identified Lagrangian coherent structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased withReand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently ofRe, the same amount of fluid remains on the stenosis over more than a pulsatile period.


Assuntos
Estenose da Valva Aórtica/diagnóstico por imagem , Modelos Cardiovasculares , Reologia , Estenose da Valva Aórtica/fisiopatologia , Hemodinâmica , Humanos , Fluxo Pulsátil , Ultrassonografia
10.
Phys Med Biol ; 65(17): 175002, 2020 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-32413874

RESUMO

High-frame-rate volume imaging (HFR-VI) aims to provide high-quality images with high-temporal information. Despite its potential, HFR-VI translation into clinical applications has been challenging due to the high cost of the equipment required to drive matrix probes with a large number of elements. The goal of this study is to introduce and test sparse-random-aperture compounding (SRAC), a technique that allows use of matrix probes with an ultrasound system that has fewer channels while maintaining high frame rates. Four scanning methods were implemented with a 256-channel system using a 4-to-1 multiplexer and a 3 MHz matrix probe with 1024 elements. These methods used three types of waves, either single-diverging waves (SDW), multiplane-diverging waves (MDW) or wide beams (WB); and were driven using one to four SRAC. All methods were also implemented in a 1024-channel multisystem. The main-lobe-to-side-lobe ratio (MLSLR) and the contrast ratio (CR) were studied using a string phantom and a CIRS phantom, respectively. The results showed an increase in the MLSLR and CR as a function of the number of SRAC. The multisystem provided the best results for the MLSLR. However, four SRAC outperformed the multisystem with respect to CR. The method using SDW provided the highest frame rates (i.e. 1875 and 7500 Hz for four and one SRAC, respectively), however it provided the lowest image quality. The two methods using MDWs showed a good compromise between image quality and frame rate (i.e. 187 to 750 Hz for four and one SRAC). WB provided the best image quality at the expense of frame rate (i.e. 18 to 75 Hz for four and one SRAC). Our results suggest that SRAC in combination with the tested scanning methods can provide a low-channel count alternative for HFR-VI systems and allows a tunable tradeoff between image quality and frame rate guided by the desired application.


Assuntos
Ultrassonografia/métodos , Humanos , Imagens de Fantasmas
11.
ACS Nano ; 14(11): 15450-15457, 2020 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-33103880

RESUMO

Cobalt oxides have been identified as highly active catalysts for the electrochemical water splitting and oxygen evolution reaction. Using near-ambient pressure resonant photoelectron spectroscopy, we studied changes in the metal-oxygen coordination of size-selected core-shell CoOx nanoparticles induced by liquid water. In dry conditions, the nanoparticles exhibit an octahedrally coordinated Co2+ core and a tetrahedrally coordinated Co2+ shell. In the presence of liquid water, we observe a reversible phase change of the nanoparticle shell into octahedrally coordinated Co2+ as well as partially oxidized octahedrally coordinated Co3+. This is in contrast to previous findings, suggesting an irreversible phase change of tetrahedrally coordinated Co2+ after the oxygen evolution reaction conditioning. Our results demonstrate the appearance of water-induced structural changes different from voltage-induced changes and help us to understand the atomic scale interaction of CoOx nanoparticles with water in electrochemical processes.

12.
Mar Environ Res ; 159: 105021, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32662445

RESUMO

Variability in body condition and energy storage has important implications for fish recruitment and ecosystem structure. Understanding strategies for energy allocation to maintenance, reproduction and growth is essential to evaluate the state of the fish stocks. In this study, we address the energetics dynamics of the annual cycle of anchovies (Engraulis encrasicolus) and sardines (Sardina pilchardus) in the north-western Mediterranean Sea using indirect and direct condition indices. We assessed and validated the use of morphometric, biochemical and energetic indices for both species. Annual patterns of the relative condition index (Kn), gonadosomatic index (GSI), lipid content (% lipids) and energy density (ED) were linked to the energy allocation strategy. Our results highlight that anchovy mainly rely on income energy to reproduce, while sardine accumulate the energy during the resting period to be used in the reproduction period. Consequently, variability in the lipid content and ED between seasons was lower in anchovy than in sardine. In both species, we observed an early decline in energy reserves in late summer-early fall, which may be related to unfavourable environmental conditions during spring and summer. Regarding the use of different condition indices, both direct indices, lipid content and ED, were highly correlated with Kn for sardine. ED was better correlated with Kn than lipid content for anchovy. For the first time, a relationship between ED of gonads and GSI for sardine and anchovy was provided, highlighting the importance of the energy invested in reproduction. This work provides new insights into the energy dynamics of sardine and anchovy. We also demonstrate which are the most suitable indices to measure changes in the physiological condition of both species, providing tools for the future monitoring of the populations of these two commercially and ecologically important fish species.


Assuntos
Ecossistema , Peixes , Animais , Metabolismo Energético , Peixes/metabolismo , Mar Mediterrâneo , Alimentos Marinhos , Estações do Ano
13.
Phys Med Biol ; 64(7): 075001, 2019 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-30736021

RESUMO

Cardiovascular disease is the leading cause of mortality in the United States. Peripheral artery disease (PAD) affects a substantial portion of the elderly population (>70 years). PAD can be symptomatic or asymptomatic, and treatment is directed towards improving functional vessel patency and limb salvage. Revascularization surgical treatments are needed in some cases, and it is not always possible to use autologous veins for vascular grafting. In this case, synthetic materials may be used. Synthetic materials such as expanded polytetrafluoroethylene (ePTFE) and poly (ethylene terephthalate) (Dacron) have been used. These materials are much stiffer compared to normal arterial vessels so developing alternative materials is an active area of research. One such potential material is a p olyvinyl alcohol cryogel reinforced arterial model (PRAM). In this study we used shear wave elastography (SWE) techniques to compare the mechanical behavior of excised aortas and anastomoses formed between the aortas and the Dacron, ePTFE, and PRAM materials. Different initial longitudinal strains (0%-40%) and transmural pressures (20-180 mmHg) were used to test a wide range of parameters that are within physiological ranges. We found that the PRAM materials had similar mechanical behavior in terms of group velocity measured in the vessel wall with respect to the excised aortas compared to the Dacron and ePTFE that had higher values of group velocity. The ratios of the group velocity for the PRAM material with respect to the aortas ranged from 0.83 to 1.13 where the Dacron and ePTFE had ranges of 1.12-2.22 and 1.91-3.10 for the same stretch and pressure ranges. The PRAM materials provide an alternative vascular material with better mechanical matching with excised aortas.


Assuntos
Prótese Vascular/normas , Técnicas de Imagem por Elasticidade , Polietilenotereftalatos/química , Politetrafluoretileno/química , Idoso , Anastomose Cirúrgica/instrumentação , Anastomose Cirúrgica/métodos , Aorta/cirurgia , Artéria Femoral/cirurgia , Humanos , Masculino , Polietilenotereftalatos/efeitos adversos , Politetrafluoretileno/efeitos adversos , Grau de Desobstrução Vascular
14.
ACS Catal ; 9(6): 5496-5502, 2019 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-31205798

RESUMO

Efficient and active catalysts with high selectivity for hydrocarbons and other valuable chemicals during stable operation are crucial. We have taken advantage of low-pressure oxygen plasmas to modify dendritic Cu catalysts and were able to achieve enhanced selectivity toward C2 and C3 products. Utilizing operando spectroscopic methods such as X-ray absorption fine-structure spectroscopy (XAFS) and quasi in situ X-ray photoelectron spectroscopy (XPS), we observed that the initial presence of oxides in these catalysts before the reaction plays an inferior role in determining their catalytic performance as compared to the overall catalyst morphology. This is assigned to the poor stability of the Cu x O species in these materials under the conditions of electrocatalytic conversion of CO2 (CO2RR). Our findings shed light into the strong structure/chemical state-selectivity correlation in CO2RR and open venues for the rational design of more effective catalysts through plasma pretreatments.

15.
Phys Med Biol ; 64(16): 165006, 2019 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-31252426

RESUMO

In this work we developed a methodology to manufacture a new type of arterial model that could be used in experimental setting instead of excised arteries while developing new imaging modalities. CT-images of the descending aorta were used to create molds with patient specific morphology. A polyvinyl alcohol (PVA) solution with a reinforcing cotton mesh was used to generate the models. The mesh is circumferentially elastic while non-compliant longitudinally and is responsible for the non-linear anisotropic mechanical behavior of the models. Two models were fabricated following the same manufacturing procedure. Their circumferential and longitudinal mechanical properties were evaluated and compared to those of excised healthy pig aortas via tensile testing. A very good agreement was found for the circumferential direction, while the longitudinal direction showed to have a more marked anisotropic behavior compared to the excise arteries. An increase from 113 kPa at 2.5% strain, to 914 kPa at 40% strain was obtained for the models, while the arteries showed an increase from 172 kPa at 2.5% strain to 922 kPa at 38% strain. Furthermore, by plugging the models into a cardiovascular simulator their mechanical response in a more realistic setting was evaluated under static and dynamic pressure conditions by using shear wave elastography (SWE). Static and dynamic experiments showed an increase in the shear modulus as a function of pressure from 61 kPa to 263 kPa, between 20 mmHg and 150 mmHg for Model 1 (similar values within 10% were obtained for Model 2). These values are in good agreement with those reported in the literature for healthy human arteries. To our knowledge the models presented in this study are the first morphologically realistic phantoms that have demonstrated nonlinear and anisotropic elastic behaviors close to those of healthy arteries.


Assuntos
Aorta/fisiologia , Técnicas de Imagem por Elasticidade/métodos , Dinâmica não Linear , Imagens de Fantasmas , Animais , Anisotropia , Aorta/diagnóstico por imagem , Estresse Mecânico , Suínos
16.
Artigo em Inglês | MEDLINE | ID: mdl-17571813

RESUMO

We describe a phase aberration correction method that uses dynamic ultrasound radiation force to harmonically vibrate an object using amplitude modulated continuous wave ultrasound. The phase of each element of an annular array transducer is adjusted to maximize the radiation force and obtain optimal focus of the ultrasound beam. The maximization of the radiation force is performed by monitoring the velocity of scatterers in the focus region. We present theory that shows focal optimization with radiation force has a well-behaved cost function. Experimental validation is shown by correction of manual defocusing of an annular array as well as correcting for a lens-shaped aberrator placed near the transducer. A Doppler laser vibrometer and a pulse-echo Doppler ultrasound method were used to monitor the velocity of a sphere used as a target for the transducer. By maximizing the radiation force-induced vibration of scatterers in the focal region, the resolution of the ultrasound beam can be recovered after aberration defocusing.


Assuntos
Algoritmos , Artefatos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Ultrassonografia/métodos , Imagens de Fantasmas , Reprodutibilidade dos Testes , Espalhamento de Radiação , Sensibilidade e Especificidade , Vibração
17.
IEEE Trans Cybern ; 47(9): 2628-2638, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27542189

RESUMO

This paper is concerned with nonquadratic conditions for stabilization of continuous-time nonlinear systems via exact Takagi-Sugeno models and generalized fuzzy Lyapunov functions. The approach hereby proposed feedback to the time derivatives of the membership functions through a multi-index control law that cancels out the terms responsible of former a priori local conditions. Thus, a nonquadratic controller design in the form of linear matrix inequalities is achieved; it does not require bounds on the time derivatives nor any extra parameters. The examples included are shown to outperform former approaches.

18.
Phys Med Biol ; 62(1): 91-106, 2017 01 07.
Artigo em Inglês | MEDLINE | ID: mdl-27973354

RESUMO

Noninvasive evaluation of the rheological behavior of soft tissues may provide an important diagnosis tool. Nowadays, available commercial ultrasound systems only provide shear elasticity estimation by shear wave speed assessment under the hypothesis of a purely elastic model. However, to fully characterize the rheological behavior of tissues, given by its storage (G') and loss (G″) moduli, it is necessary to estimate both: shear wave speed and shear wave attenuation. Most elastography techniques use the acoustic radiation force to generate shear waves. For this type of source the shear waves are not plane and a diffraction correction is needed to properly estimate the shear wave attenuation. The use of a cylindrical wave approximation to evaluate diffraction has been proposed by other authors before. Here the validity of such approximation is numerically and experimentally revisited. Then, it is used to generate images of G' and G″ in heterogeneous viscoelastic mediums. A simulation algorithm based on the anisotropic and viscoelastic Green's function was used to establish the validity of the cylindrical approximation. Moreover, two experiments were carried out: a transient elastography experiment where plane shear waves were generated using a vibrating plate and a SSI experiment that uses the acoustic radiation force to generate shear waves. For both experiments the shear wave propagation was followed with an ultrafast ultrasound scanner. Then, the shear wave velocity and shear wave attenuation were recovered from the phase and amplitude decay versus distance respectively. In the SSI experiment the cylindrical approximation was applied to correct attenuation due to diffraction effects. The numerical and experimental results validate the use of a cylindrical correction to assess shear wave attenuation. Finally, by applying the cylindrical correction G' and G″ images were generated in heterogeneous phantoms and a preliminary in vivo feasibility study was carried out in the human liver.


Assuntos
Técnicas de Imagem por Elasticidade/métodos , Algoritmos , Anisotropia , Elasticidade , Humanos , Modelos Teóricos , Imagens de Fantasmas , Reologia , Viscosidade
19.
Sci Transl Med ; 9(411)2017 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-29021168

RESUMO

Functional neuroimaging modalities are crucial for understanding brain function, but their clinical use is challenging. Recently, the use of ultrasonic plane waves transmitted at ultrafast frame rates was shown to allow for the spatiotemporal identification of brain activation through neurovascular coupling in rodents. Using a customized flexible and noninvasive headmount, we demonstrate in human neonates that real-time functional ultrasound imaging (fUSI) is feasible by combining simultaneous continuous video-electroencephalography (EEG) recording and ultrafast Doppler (UfD) imaging of the brain microvasculature. fUSI detected very small cerebral blood volume variations in the brains of neonates that closely correlated with two different sleep states defined by EEG recordings. fUSI was also used to assess brain activity in two neonates with congenital abnormal cortical development enabling elucidation of the dynamics of neonatal seizures with high spatiotemporal resolution (200 µm for UfD and 1 ms for EEG). fUSI was then applied to track how waves of vascular changes were propagated during interictal periods and to determine the ictal foci of the seizures. Imaging the human brain with fUSI enables high-resolution identification of brain activation through neurovascular coupling and may provide new insights into seizure analysis and the monitoring of brain function.


Assuntos
Encéfalo/diagnóstico por imagem , Ultrassonografia/métodos , Encéfalo/fisiologia , Mapeamento Encefálico , Eletroencefalografia , Feminino , Humanos , Recém-Nascido , Masculino , Convulsões/diagnóstico por imagem , Convulsões/fisiopatologia
20.
Artigo em Inglês | MEDLINE | ID: mdl-26625412

RESUMO

Breast cancer detection in the early stages is of great importance since the prognosis, and the treatment depends more on this. Multiple techniques relying on the mechanical properties of soft tissues have been developed to help in early detection. In this study, we implemented a technique that measures the nonlinear shear modulus (NLSM) (µ(NL)) in vivo and showed its utility to detect breast lesions from healthy tissue. The technique relies on the acoustoelasticity theory in quasi-incompressible media. In order to recover µ(NL), static elastography and supersonic shear imaging are combined to subsequently register strain maps and shear modulus maps while the medium is compressed. Then, µ(NL) can be recovered from the relationship between the stress, deduced from strain maps, and the shear modulus. For this study, a series of five nonlinear phantoms were built using biological tissue (pork liver) inclusions immersed in an agar-gelatin gel. Furthermore, 11 in vivo acquisitions were performed to characterize the NLSM of breast tissue. The phantom results showed a very good differentiation of the liver inclusions when measuring µ(NL) with a mean value of -114.1 kPa compared to -34.7 kPa for the gelatin. Meanwhile, values for the shear modulus for the liver and the gelatin were very similar, 3.7 and 3.4 kPa, respectively. In vivo NLSM mean value for the healthy breast tissue was of -95 kPa, while mean values of the benign and the malignant lesions were -619 and -806 kPa with a strong v ariability, respectively. This study shows the potential of the acoustoelasticity theory in quasi-incompressible medium to bring a new parameter for breast cancer diagnosis.


Assuntos
Neoplasias da Mama/diagnóstico por imagem , Neoplasias da Mama/fisiopatologia , Animais , Módulo de Elasticidade/fisiologia , Estudos de Viabilidade , Feminino , Humanos , Fígado/diagnóstico por imagem , Dinâmica não Linear , Imagens de Fantasmas , Suínos , Ultrassonografia
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