C. Negreira

University of the Republic, Uruguay, Ciudad de Montevideo, Montevideo, Uruguay

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Publications (55)20.76 Total impact

  • J. BRUM · I. BAZAN · A. RAMOS · C. NEGREIRA · A. RAMIREZ · L. DIEZ
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    ABSTRACT: The detection of changes in the properties of the walls in blood vessels (e.g. modifications in thickness or elasticity) is a promising way for the early diagnosis of cardiovascular diseases (e.g. atherosclerosis), and some attempts have been made using classic ultrasonic images. However, to obtain a reliable non invasive estimation of these changes still presents many challenges that must be overcome, in particular, to achieve an accurate estimation of the vessel wall thickness, which usually is associated to strain and elasticity alterations happening before the cardiovascular disease presents clinical symptom; to solve efficiently these aspects is a very difficult task. In this work, the application to vessels of a recent ultrasonic method developed by the authors for estimating wall thicknesses is described. This method (based on high-resolution power spectral density - PSD) and its algorithmic responses were tested on an arterial phantom under physiological conditions of flow and pressure, and some results are compared to those obtained using a direct-time thickness estimation and with the resolutions related to our alternative cross-correlation option shown in previous papers. A higher spatial resolution is obtained, for experimental multi-pulse ultrasonic echoes, with this PSD method in comparison to those based on conventional echography, cross correlation operators or other spectral options.
    No preview · Article · Dec 2015 · Physics Procedia
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    G Cortela · N Benech · W C A Pereira · C Negreira
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    ABSTRACT: Stability and duration of ultrasonic (US) Phantoms are still a subject of research. We present a study of acoustic and mechanical properties for polyvinyl chloride plastisol (PVCP) with graphite powder (at 2% in weight) used to construct tissue-like phantoms in the temperature range of 20-45C. PVCP is a new material in the field of US phantoms and has longer duration and stability than the conventional organic mimicking materials. Longitudinal US velocity and attenuation were measured at 1 MHz by the standard transmission method. Shear velocity was obtained by 1-D transient elastography. The extreme values for each of the parameters were obtained at 20 C and 45C. They are: 1501.5±0.7 m/s and 1331.8±0.3 m/s for longitudinal US velocity; 0.46±0.03 dB/cm and 0.94±0.09 dB/cm for attenuation; and 8.4±1.2 m/s and 1.7±0.8 m/s for Shear velocity. Specific heat measured with a calorimeter and thermal conductivity measured by the method of hot plates were, respectively, 2.65±0.51 J/(kgC) and 0.091±0.013J/(s°Cm), both at 22°C. For 2% of graphite powder, the parameter ranges were compatible to biological tissue ones and therefore, the same phantom can simulate different conditions only by changing its temperature. Other graphite percentages are to be tested to simulate parameter values of pathological conditions like nodules, calcification, fibrosis, etc. The phantom did not suffer from dehydration and is easy to be built in several different geometries.
    Full-text · Article · Dec 2015 · Physics procedia
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    ABSTRACT: Development of successful small-diameter vascular grafts constitutes a real challenge to biomaterial engineering. In most cases these grafts fail in-vivo due to the presence of a mechanical mismatch between the native vessel and the vascular graft. Biomechanical characterization of real native vessels provides significant information for synthetic graft development. Electrospun nanofibrous vascular grafts emerge as a potential tailor made solution to this problem. PLLA-electrospun nanofibrous tubular structures were prepared and selected as model bioresorbable grafts. An experimental setup, using gold standard and high resolution ultrasound techniques, was adapted to characterize in vitro the poly(l-lactic acid) (PLLA) electrospun structures. The grafts were subjected to near physiologic pulsated pressure conditions, following the pressure-diameter loop approach and the criteria stated in the international standard for cardiovascular implants-tubular vascular prostheses. Additionally, ovine femoral arteries were subjected to a similar evaluation. Measurements of pressure and diameter variations allowed the estimation of dynamical compliance (%C, 10(-2)mmHg) and the pressure-strain elastic modulus (EPε, 10(6)dyncm(-2)) of the abovementioned vessels (grafts and arteries). Nanofibrous PLLA showed a decrease in %C (1.38±0.21, 0.93±0.13 and 0.76±0.15) concomitant to an increase in EPε (10.57±0.97, 14.31±1.47 and 17.63±2.61) corresponding to pressure ranges of 50 to 90mmHg, 80 to 120mmHg and 100 to 150mmHg, respectively. Furthermore, femoral arteries exhibited a decrease in %C (8.52±1.15 and 0.79±0.20) and an increase in EPε (1.66±0.30 and 15.76±4.78) corresponding to pressure ranges of 50-90mmHg (elastin zone) and 100-130mmHg (collagen zone). Arterial mechanics framework, extensively applied in our previous works, was successfully used to characterize PLLA vascular grafts in vitro, although its application can be directly extended to in vivo experiences, in conscious and chronically instrumented animals. The specific design and construction of the electrospun nanofibrous PLLA vascular grafts assessed in this work, showed similar mechanical properties as the ones observed in femoral arteries, at the collagen pressure range. Copyright © 2014 Elsevier B.V. All rights reserved.
    No preview · Article · Dec 2014 · Materials Science and Engineering C
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    ABSTRACT: This paper presents an instrument that uses electronic technologies to characterize the effects of diabetes by measuring the changes of the tissue physical characteristics, mainly in the foot. The instrument comprises 1) the measurement of glucose, 2) IR temperature measurement of the foot, 3) the differentiation of staining in areas of the foot, 4) the determination of the elasticity of vessels and foot tissues, 5) the determination of muscle impedance, 6) the recording of the variation of the patient heart rate, 7) software that concentrates the digital information of the measured characteristics of the foot and a display to show the information to the physician. This article describes the results of temperature measurement on the sole of a foot, the patient result storage, a measurement method with RF impedance and the temperature of the foot taken with a commercial IR camera.
    No preview · Conference Paper · Nov 2014
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    ABSTRACT: In the manufacturing of cheese, the cutting of the curd is an essential step which depends on the firmness of the curds and significantly affects the yield of the cheese and its quality. In this work, we present a technique to measure elastic properties of the curd during coagulation that could be used to quantitatively determine the cutting time. The technique uses ultrasound to generate and measure shear waves. These waves do not propagate in liquids and their velocity of propagation depends on the viscoelastic characteristics of the medium. Hence, they can be used to identify the beginning of coagulation and subsequently to monitor the evolution of the coagulum firmness. Our results showed this technique is sensitive to changes of the medium structure during coagulation. It also proved reproducible and sensitive to different coagulation conditions. Therefore this technique can be used to develop a system suitable for the dairy industry.
    No preview · Article · Sep 2014 · Journal of Food Engineering
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    ABSTRACT: Quantification of fluid-structure interactions in arterial walls requires to achieve a complete characterization of flow, shear stress in the interface between blood and endothelium, wall elasticity and wall stresses distribution. Diameter change vs. intravascular pressure is the basis to estimate biomechanical properties (e.g. elasticity, viscosity) of arterial walls in-vivo or in-vitro, being sonomicrometry the gold standard for vessel diameter measurement. High resolution ultrasonography (HRU) is used here in-vitro (as an alternative to sonomicrometry) to get an adequate estimation of the diameter without disturbing the vessel dynamics. Some experimental in-vitro results are shown for a physical model of arterial bifurcation surgically implemented from a sample of fresh porcine aorta, with and without asymmetric stenosis. Near-physiologic pulsated flow conditions were reproduced in-vitro using a specially designed hemodynamic work bench simulator (HWBS). In-silico results obtained from a simple CFD model of the abovementioned bifurcation are presented. Boundary conditions were applied from in-vitro HWBS experimental measurements. Levels of stenosis were reproduced in-silico. Properly tuned digital simulation based on in-vitro experimental data using our HWBS allows the determination of physical magnitudes (like shear stress) that can’t be obtained easily in experimental in-vitro measurements.
    No preview · Article · Jan 2014 · IFMBE proceedings
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    ABSTRACT: The quantification of fluid-structure interactions in arterial walls (from a biomechanical standpoint) requires a complete characterization of blood flow, shear stress in the interface between blood and endothelium, wall elasticity and wall stresses distribution. These interactions play an important role in pathogenic mechanisms of cardiovascular diseases, such as atherosclerosis and arteriosclerosis. A specific hemodynamic work bench simulator is used for an in-vitro characterization of the biomechanics and hemodynamics of a custom constructed physical model of arterial bifurcation, under near-physiologic pulsated flow conditions. The model was constructed using fresh porcine aorta. Some experimental in-vitro results are shown. In-vitro results are compared with in-silico results obtained from a simple CFD model of the abovementioned bifurcation. Experimental data allow construction of meshes and parameter estimation of the biomechanical properties of the arterial wall, as well as boundary conditions, all suitable to be employed in CFD and FSI numerical simulation. In-silico simulations enables the estimation of some parameters that cannot be easily obtained by means of in-vitro experimental measurements (for example wall shear stress).
    No preview · Article · Dec 2013 · Journal of Physics Conference Series
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    ABSTRACT: To quantify fluid-structure interactions in arterial walls, from a biomechanical standpoint, a complete characterization of blood flow, shear stress in the interface between blood and endothelium, wall elasticity and wall stresses distribution are needed.
    No preview · Article · Jul 2013 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
  • N Benech · J Brum · S Catheline · T Gallot · C Negreira
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    ABSTRACT: In a lossless system, the causal and acausal Green's function for elastic waves can be retrieved by cross-correlating the elastic field at two positions. This field, composed of converging and diverging waves, is interpreted in the frame of a time-reversal process. In this work, the near-field effects on the spatio-temporal focusing of elastic waves are analyzed through the elastodynamic Green's function. Contrary to the scalar field case, the spatial focusing is not symmetric preserving the directivity pattern of a simple source. One important feature of the spatial asymmetry is its dependency on the Poisson ratio of the solid. Additionally, it is shown that the retrieval of the bulk wave speed values is affected by diffraction. The correction factor depends on the relative direction between the source and the observed field. Experimental verification of the analysis is carried out on the volume of a soft-solid. A low-frequency diffuse-like field is generated by random impacts at the sample's free surface. The displacement field is imaged using ultrasound by a standard speckle tracking technique. One important application of this work is in the estimation of the shear elastic modulus in soft biological tissues, whose quantification can be useful in non-invasive diagnosis of various diseases.
    No preview · Article · May 2013 · The Journal of the Acoustical Society of America
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    A. RAMOS · I. BAZAN · C. NEGREIRA · J. BRUM · A. ROSALES · F. GALLEGOS
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    ABSTRACT: Abstract –– Research looking for the achieving of an accurate measurement of thickness changes in thin biological walls (e.g. of blood vessels), is a promising work line in the medical area, because it would provide the bases to analyze the possibility of attaining early diagnoses of some diseases such as hypertension or atherosclerosis. But, to obtain a non-invasive estimation of these parameters on internal tissues, currently presents many difficulties that must be overcome. The use of high-frequency ultrasonic systems appears to offer a possible solution. In fact, the application of conventional ultrasonic imaging has shown this, but the spatial resolution related to this commercial option is not sufficient for a thickness evaluation with sufficient clinical significance, which would require accuracies of few microns. In this paper, some preliminary results of applying a new broadband ultrasonic procedure, recently developed by the authors for thickness measurement purposes, are analyzed for sub-millimeter layers made of materials similar (phantoms) to that of the biological tissues to be encountered into the artery walls. Two optional algorithms for estimating the power spectral density of the multi-pulse signals are assessed with some experimental echoes. Their potential resolutions and capabilities to provide accuracies around a micron are comparatively analyzed, for walls thickness estimation.
    Full-text · Conference Paper · Apr 2013
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    F. GAMINO · I. BAZÁN · A. RAMÍREZ · A. RAMOS · C. NEGREIRA
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    ABSTRACT: The spectral analysis techniques has been widely used to extract information about certain signals and the process in which those are generated. Ultrasonic (US) signal acquired from biological tissues are a particular case of that. Spectral analysis has been used to extract information from US signal related to biological tissue condition, mainly related with the internal scattering structure distribution and regularity. High-resolution spectral analysis techniques are applied to determine pathological characteristics that could indicate the presence of disease in the tissue. Some small changes in harmonics location could be drastically affected by the presence of noise in the analyzed signal. In this work, an evaluation of two parametric HR spectral analysis techniques is performed, first applied to signals acquired from a biological tissue phantom in a temperature range from 21°C to 45°C. A second evaluation was performed, considering simulated US signals, which were added with three different levels of SNR, and then they were analyzed with two parametric methods, which present variations in the error estimated for different noise level conditions. But the general behavior is a smaller error when noise decreases.
    Full-text · Conference Paper · Apr 2013
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    A. RAMOS · C. NEGREIRA · I. BAZAN · J. BRUM

    Full-text · Conference Paper · Jan 2013
  • J. Brum · D. Bia · N. Benech · G. Balay · R. Armentano · C. Negreira
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    ABSTRACT: In this work a new method, based in ultrasonography, to quantify arterial diameter is discussed and compared with the gold standart method: sonomicrometry. The results indicated that the new method ensure an optimal diameter quantification.
    No preview · Article · Jan 2013 · IFMBE proceedings
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    E. Budelli · N. Pérez · P. Lema · C. Negreira
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    ABSTRACT: Experimental determination of time of flight and attenuation has been proposed in the literature as alternatives to monitoring the evolution of milk coagulation during cheese manufacturing. However, only laboratory scale procedures have been described. In this work, the use of ultrasonic time of flight and attenuation to determine cutting time and its feasibility to be applied at industrial scale were analyzed. Limitations to implement these techniques at industrial scale are shown experimentally. The main limitation of the use of time of flight is its strong dependence with temperature. Attenuation monitoring is affected by a thin layer of milk skin covering the transducer, which modifies the signal in a non-repetitive way. The results of this work can be used to develop alternative ultrasonic systems suitable for application in the dairy industry.
    Full-text · Article · Dec 2012 · IOP Conference Series Materials Science and Engineering
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    E Budelli · N Perez · S Barrios · G Ares · R Canetti · C Negreira
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    ABSTRACT: El cambio en la velocidad de propagación de ondas ultrasónicas ha sido propuesto como un método para el monitoreo en línea del proceso de coagulación enzimática de leche para la fabricación de queso. El objetivo de este trabajo fue estudiar la influencia de la condición de contorno de temperatura sobre las medidas de tiempo de vuelo (tv) de ondas de compresión durante este proceso. La coagulación se realizó utilizando leche pasteurizada entera a 35 ºC adicionada de CaCl2 y quimosina. Se realizaron medidas de textura instrumental y ultrasónicas en paralelo. Se registró la fuerza en función del tiempo mediante ensayos de extrusión inversa con una sonda cilíndrica plana en un texturómetro TA.XT2i. Para las medidas ultrasónicas se utilizó una celda prismática, en la cual se introdujo un transductor de 3.5 MHz en una de las paredes laterales, registrándose el primer eco reflejado en la pared opuesta. Para este eco se calculó la variación en el tv durante el proceso de coagulación. Durante el proceso de coagulación la fuerza máxima y el tv aumentaron, mientras que la temperatura dentro de la celda de ultrasonido descendió. Se obtuvo una buena correlación entre el tv y la fuerza máxima (R2=0.94) y entre el tv y la temperatura (R2=0.93). Cuando la temperatura de contorno se mantuvo igual que la del medio se registró un aumento en la fuerza máxima pero variaciones no significativas en el tv. Estos resultados permiten concluir que las variaciones en el tv responden a variaciones en la temperatura dentro de la celda de coagulación y no a cambios en la estructura durante el proceso. Esto limita la aplicación de esta técnica para el monitoreo de la coagulación de la leche. http://aiquruguay.org/congreso/download/P83.pdf
    Full-text · Conference Paper · Nov 2012
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    ABSTRACT: To achieve a precise noninvasive temperature estimation, inside patient tissues, would open promising research fields, because its clinic results would provide early-diagnosis tools. In fact, detecting changes of thermal origin in ultrasonic echo spectra could be useful as an early complementary indicator of infections, inflammations, or cancer. But the effective clinic applications to diagnosis of thermometry ultrasonic techniques, proposed previously, require additional research. Before their implementations with ultrasonic probes and real-time electronic and processing systems, rigorous analyses must be still made over transient echotraces acquired from well-controlled biological and computational phantoms, to improve resolutions and evaluate clinic limitations. It must be based on computing improved signal-processing algorithms emulating tissues responses. Some related parameters in echo-traces reflected by semiregular scattering tissues must be carefully quantified to get a precise processing protocols definition. In this paper, approaches for non-invasive spectral ultrasonic detection are analyzed. Extensions of author's innovations for ultrasonic thermometry are shown and applied to computationally modeled echotraces from scattered biological phantoms, attaining high resolution (better than 0.1 °C). Computer methods are provided for viability evaluation of thermal estimation from echoes with distinct noise levels, difficult to be interpreted, and its effectiveness is evaluated as possible diagnosis tool in scattered tissues like liver.
    Full-text · Article · May 2012 · Computational and Mathematical Methods in Medicine
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    ABSTRACT: Some biological tissues, such as skeletal muscle, have regular or quasi-periodic structures. Periodicity of these structures can be investigated by spectral methods based on ultrasonic backscattered signals. These methods estimate the Mean Scatterer Spacing (MSS). In this work we analyzed the MSS dependence with temperature in bovine skeletal muscle tissue samples. Through spectral analysis we found that the relative variation of the MSS, in the temperature range 20 - 48°C was of ~ 2% /°C. For the same sample and under the same experimental conditions, we analyzed the propagation velocity of shear waves by transient elastography. It was determined that the relative variation of shear elastic modulus was ~ 3% /°C in the same temperature range. The repeatability of the results was tested in three tissue samples, with a set of 6 measurements on each. The relative variation is therefore similar for both parameters. Thus, this study shows that both techniques can be used as a method of noninvasive thermometry for small temperature range. In addition we emphasize the conceptual differences between both methods. As temperature changes, MSS estimation varies due to two physical phenomena. An apparent variation in mean spacing is produced because the sound speed is temperature-dependent, while tissue expansion produces a real change. In practice it is difficult to discriminate the weight of each component in the MSS variation. On the other side, transient elastography is less sensitive to thermal expansion. Thus it measures the actual shear wave speed change with temperature. This differentiation between both methods could be used to construct useful thermoelastic models for soft tissues in the future.
    No preview · Article · May 2012
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    ABSTRACT: Parametric algorithms previously developed by authors for spectral evaluation of biological multi-echo waveforms are adapted and improved here in order to achieve a more elevated frequency resolution. These results permit to undertake viability studies around the possible application of a new auto-regressive spectral technique to estimate physical properties like wall thickness changes in blood vessels, with accuracy enough. These difficult and sophisticated measurements in vessels have an increasing interest as tools to estimate basic parameters for calculating elastic properties in the vessel walls. Laboratory thickness data obtained for a latex phantom (mimicking vessel properties) are shown, giving a promising expectative for this improved estimation technique in blood vessels characterization, a diagnostic tool nowadays of growing attention by the researches. In fact, the results suggest clear improvement in spatial resolution, over the classic cross-correlation and non-parametric techniques, to estimate delays between pulsed signals. But, still further efforts and rigorous analyses of ultrasonic echo-signals acquired from well-controlled sanguineous tissues phantoms are needed in order to optimize the potential resolution of this new thickness measurement procedure and also to evaluate its possible clinic limitations.
    Full-text · Article · Mar 2012
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    ABSTRACT: Paper invitado
    Full-text · Conference Paper · Jan 2012
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    I. BAZAN · A. RAMOS · C. NEGREIRA · H. CALAS · T.E GOMEZ · J. BRUM

    Full-text · Conference Paper · Jan 2012

Publication Stats

155 Citations
20.76 Total Impact Points

Institutions

  • 2014
    • University of the Republic, Uruguay
      Ciudad de Montevideo, Montevideo, Uruguay
  • 2006-2014
    • Universidad de Montevideo
      Ciudad de Montevideo, Montevideo, Uruguay
  • 2005
    • The Police Academy of the Czech Republic in Prague
      Praha, Praha, Czech Republic