demian pereira - Academia.edu (original) (raw)

Papers by demian pereira

Research paper thumbnail of Uso de ensayos no destructivos (radiografía con rayos x) para la determinación de calidad de muestras de suelo obtenidas en sondeos geotécnicos costa afuera

Research paper thumbnail of Fractal Properties and Critical Exponents in Tumor

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image that clearly define the active region of the tumor and its border. In the present work, nosologic maps were obtained combining T2-weighted magnetic resonance images with in vivo magnetic resonance spectroscopy information on brain tumors. The image was segmented according to the nosologic map and tumor contours were determined. Several fractal properties were determined on the contour: the capacity or fractal dimension, the correlation dimension for a temporal series constructed from the original contour, and also a critical exponent coming from the contour roughness. The results obtained showed a good correlation between the roughness critical exponent and the degree of malignancy of the tumor.

Research paper thumbnail of Uso de ensayos no destructivos (radiografía con rayos x) para la determinación de calidad de muestras de suelo obtenidas en sondeos geotécnicos costa afuera

Research paper thumbnail of Automated Extraction, Fractal Characterization and Automatic Classification of Tumors of the Central Nervous System

Research paper thumbnail of Caracterización de Malignidad en Tumores del Sistema Nervioso Central Mediante Análisis Fractal

Research paper thumbnail of Evaluación De La Calidad De Adherencia en La Interfase Metal-Elastómero en Probetas Normalizadas Mediante Ultrasonido

This paper presents studies on the feasibility of applying ultrasonic non destructive testing tec... more This paper presents studies on the feasibility of applying ultrasonic non destructive testing techniques to determine the bonding quality at the metal-elastomer interface of standardized test samples that simulate the interface of progressive cavity pumps employed in oil wells artificial lift. The ultrasonic nondestructive inspection was carried out on test samples specially prepared to perform bonding tests according to standard ASTM D429. Different types of samples that simulated a variety of interface conditions were prepared. The influence of the surface preparation at the interface was evaluated as well as the variations of the scattered ultrasonic frequency spectrum with the interface conditions. As a result of the measurements it could be concluded that frequencies of 5 and 10 MHz allow for a better sampling of the interface. It was also determined that the presence of trapped air bubbles and other contaminants such as oil, can significantly affect the ultrasonic signal, reve...

Research paper thumbnail of Deformable Models (Snakes) for Fractal Analysis of Brain Tumors on T2 -Weighted Images, Joint Annual Meeting ISMRM – ESMRMB, 2007, Berlin, Germany

Premature detection and classification for a disease process, is one of the most important object... more Premature detection and classification for a disease process, is one of the most important objectives for a physician. In reference to the brain, MRI can detect abnormal structures from the early stages of development, showing the morphological characteristics of neoplasic tissue, specifically the presence of rugosity or irregularities on its boundaries. The main goal in this work is to employ the rugosity on the boundary of the lesion to classify a mass as belonging to any of the two kinds of lesions (benign or malign) present in T2-weighted MRI images of the brain. To reach this goal, tumor image is segmented and a deformable model (snake) is adapted to the boundary of the lesion. The energy density functional obtained from the deformable model is analyzed as an artificial time series to determine fractal correlation dimension. Also the fractal capacity dimension was calculated on the same model. To validate the proposed methodology, it was applied to a significant number of images with different types of lesions to establish a reliable classification method.

Research paper thumbnail of Fractal properties and critical exponents in tumor

Ciencia, Jan 1, 2011

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image that clearly define the active region of the tumor and its border. In the present work, nosologic maps were obtained combining T 2 -weighted magnetic resonance images with in vivo magnetic resonance spectroscopy information on brain tumors. The image was segmented according to the nosologic map and tumor contours were determined. Several fractal properties were determined on the contour: the capacity or fractal dimension, the correlation dimension for a temporal series constructed from the original contour, and also a critical exponent coming from the contour roughness. The results obtained showed a good correlation between the roughness critical exponent and the degree of malignancy of the tumor.

Research paper thumbnail of Fractal Properties and Critical Exponents for Tumor Staging and Classification

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image to clearly define the active region of the tumor and its border. In the present work, T1 and T2 weighted magnetic resonance images of brain tumors were used to construct a nosologic map using in vivo magnetic resonance spectroscopy and biopsy for tissue classification and reference tumor staging. Different segmentation procedures were performed on the images, including gray level threshold and deformable contours (snakes). Several fractal properties were determined on the contour: the capacity or fractal dimension and the correlation dimension for different time series constructed from the original contour. Also a critical exponent coming from the contour roughness was calculated. The results obtained showed a good correlation between the rou...

Research paper thumbnail of Deformable Models (Snakes) for Fractal Analysis of Brain Tumors on T2-Weighted Images

Premature detection and classification for a disease process, is one of the most important object... more Premature detection and classification for a disease process, is one of the most important objectives for a physician. In reference to the brain, MRI can detect abnormal structures from the early stages of development, showing the morphological characteristics of neoplasic tissue, specifically the presence of rugosity or irregularities on its boundaries.

Research paper thumbnail of Diseño, Construcción y Puesta a Punto de un Tomógrafo por Ultrasonido para la Reconstrucción de Imágenes en 2D

En este trabajo se presenta el diseño, la construcción y la puesta a punto de un primer prototipo... more En este trabajo se presenta el diseño, la construcción y la puesta a punto de un primer prototipo de tomógrafo ultrasónico por transmisión, con miras a su aplicación en el área de la física médica. Las imágenes obtenidas corresponden al plano axial del objeto de estudio por medio de técnicas de reconstrucción algebraicas (ART, del inglés "Algebraic Reconstruction Technique") y retroproyección filtrada. El laboratorio de soporte instrumental, propuso la construcción de este tomógrafo ultrasónico, por lo tanto el diseño y su construcción estan basados en los requerimientos exigidos por este laboratorio. También, facilitó la instrumentación y parte de los materiales empleados en la construcción, por lo que las dificultades relacionadas con, financiamiento, disponibilidad o construcción de partes mecánicas y electrónicas, dictaron pautas importantes en el diseño propuesto. Otra de las limitaciones implícitas en el desarrollo del trabajo lo constituyen el tiempo de dedicación y...

Research paper thumbnail of Detección de Bordes Tumorales Mediante Contornos Activos (Snake) y Caracterización Mediante Análisis de Series Temporales

Research paper thumbnail of Evaluation of malignancy in tumors of the central nervous system using fractal dimension

In this work, we propose the use of the concepts of Fractal Dimension and Digital Image Processin... more In this work, we propose the use of the concepts of Fractal Dimension and Digital Image Processing, as a possible methodology to characterize the degree of malignancy of neoplastic structures located in the Central Nervous System. The images were detected by Magnetic Resonance Imaging (MRI) techniques including Proton Density, T 1 , and T 2 images. Malignant lesions (Gliomas) were compared with benign ones (Cysts). The Correlation Dimension, Lyapunov Exponents and Information Dimension were used as the relevant geometrical properties to characterize the irregular edge present in a particular structure. The edge was obtained by means of an edge detector operator and afterwards a codification procedure based on Fourier Descriptors was used to generate a numerical array or Time Series. The analysis of the processed images revealed that the relevant geometrical properties exhibit a different behavior in the case of gliomas compared to cystic lesions, a fact that can be used by the physician as an auxiliary tool to evaluate the malignancy of neoplastic structures in the brain.

Research paper thumbnail of Prototype of Stereoscopic Vision System to Improve the Image Quality in Turbid Waters during Underwater Inspections

OCEANS 2006, 2006

Underwater Visual Inspection is one of the main Non-Destructive Testing (NDT) techniques that can... more Underwater Visual Inspection is one of the main Non-Destructive Testing (NDT) techniques that can give us an accurate idea of the condition of any structure placed underwater. However, water and everything within affect light, compromising vision acuity and Inspector judgement. This work explores the possibility to compensate the side effects that light reflection and scattering (caused by turbidity) produce in

Research paper thumbnail of Glasslike ultrasonic properties of Dominican amber above helium temperatures

Journal of Applied Physics, 1991

ABSTRACT Measurements of the ultrasonic attenuation and relative velocity changes of longitudinal... more ABSTRACT Measurements of the ultrasonic attenuation and relative velocity changes of longitudinal waves of frequencies between 5 and 25 MHz are reported for clear yellow Dominican amber at low temperatures. Between 4 and 130 K the attenuation and velocity change are glasslike in their temperature and frequency dependencies. At higher temperatures both properties seemed to be affected by the α or β viscoelastic relaxations. Similar ultrasonic behavior is reported for commercial polymethylmethacrylate. Our results at low temperatures compare well quantitatively with data of other organic and inorganic glasses, except for the stronger logarithmic frequency‐dependent velocity change which is observed for both materials.

Research paper thumbnail of Multi-coil eddy current anisotropy detection probe

NDT & E International, 1995

Research paper thumbnail of Viscoelastic relaxation at megahertz frequencies in a Guasare (Venezuela) coal

Fuel, 1994

Ultrasonic attenuation and the fractional sound velocity shift for propagation parallel to beddin... more Ultrasonic attenuation and the fractional sound velocity shift for propagation parallel to bedding planes have been measured from liquid helium at room temperature in low-rank coal of south American origin in the frequency range 4 to 25 MHz. A previously unreported strong δ-...

Research paper thumbnail of Fractal Analysis of Tumoral Lesions in Brain

In this work, it is proposed a method for supervised characterization and classification of tumor... more In this work, it is proposed a method for supervised characterization and classification of tumoral lesions in brain, based on the analysis of irregularities at the lesion contour on T2-weighted MR images. After the choice of a specific image, a segmentation procedure with a threshold selected from the histogram of intensity levels is applied to isolate the lesion, the contour is detected through the application of a gradient operator followed by a conversion to a ";time series"; using a chain code procedure. The correlation dimension is calculated and analyzed to discriminate between normal or malignant structures. The results found showed that it is possible to detect a differentiation between benign (cysts) and malignant (gliomas) lesions suggesting the potential of this method as a diagnostic tool.

Research paper thumbnail of Uso de ensayos no destructivos (radiografía con rayos x) para la determinación de calidad de muestras de suelo obtenidas en sondeos geotécnicos costa afuera

Research paper thumbnail of Fractal Properties and Critical Exponents in Tumor

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image that clearly define the active region of the tumor and its border. In the present work, nosologic maps were obtained combining T2-weighted magnetic resonance images with in vivo magnetic resonance spectroscopy information on brain tumors. The image was segmented according to the nosologic map and tumor contours were determined. Several fractal properties were determined on the contour: the capacity or fractal dimension, the correlation dimension for a temporal series constructed from the original contour, and also a critical exponent coming from the contour roughness. The results obtained showed a good correlation between the roughness critical exponent and the degree of malignancy of the tumor.

Research paper thumbnail of Uso de ensayos no destructivos (radiografía con rayos x) para la determinación de calidad de muestras de suelo obtenidas en sondeos geotécnicos costa afuera

Research paper thumbnail of Automated Extraction, Fractal Characterization and Automatic Classification of Tumors of the Central Nervous System

Research paper thumbnail of Caracterización de Malignidad en Tumores del Sistema Nervioso Central Mediante Análisis Fractal

Research paper thumbnail of Evaluación De La Calidad De Adherencia en La Interfase Metal-Elastómero en Probetas Normalizadas Mediante Ultrasonido

This paper presents studies on the feasibility of applying ultrasonic non destructive testing tec... more This paper presents studies on the feasibility of applying ultrasonic non destructive testing techniques to determine the bonding quality at the metal-elastomer interface of standardized test samples that simulate the interface of progressive cavity pumps employed in oil wells artificial lift. The ultrasonic nondestructive inspection was carried out on test samples specially prepared to perform bonding tests according to standard ASTM D429. Different types of samples that simulated a variety of interface conditions were prepared. The influence of the surface preparation at the interface was evaluated as well as the variations of the scattered ultrasonic frequency spectrum with the interface conditions. As a result of the measurements it could be concluded that frequencies of 5 and 10 MHz allow for a better sampling of the interface. It was also determined that the presence of trapped air bubbles and other contaminants such as oil, can significantly affect the ultrasonic signal, reve...

Research paper thumbnail of Deformable Models (Snakes) for Fractal Analysis of Brain Tumors on T2 -Weighted Images, Joint Annual Meeting ISMRM – ESMRMB, 2007, Berlin, Germany

Premature detection and classification for a disease process, is one of the most important object... more Premature detection and classification for a disease process, is one of the most important objectives for a physician. In reference to the brain, MRI can detect abnormal structures from the early stages of development, showing the morphological characteristics of neoplasic tissue, specifically the presence of rugosity or irregularities on its boundaries. The main goal in this work is to employ the rugosity on the boundary of the lesion to classify a mass as belonging to any of the two kinds of lesions (benign or malign) present in T2-weighted MRI images of the brain. To reach this goal, tumor image is segmented and a deformable model (snake) is adapted to the boundary of the lesion. The energy density functional obtained from the deformable model is analyzed as an artificial time series to determine fractal correlation dimension. Also the fractal capacity dimension was calculated on the same model. To validate the proposed methodology, it was applied to a significant number of images with different types of lesions to establish a reliable classification method.

Research paper thumbnail of Fractal properties and critical exponents in tumor

Ciencia, Jan 1, 2011

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image that clearly define the active region of the tumor and its border. In the present work, nosologic maps were obtained combining T 2 -weighted magnetic resonance images with in vivo magnetic resonance spectroscopy information on brain tumors. The image was segmented according to the nosologic map and tumor contours were determined. Several fractal properties were determined on the contour: the capacity or fractal dimension, the correlation dimension for a temporal series constructed from the original contour, and also a critical exponent coming from the contour roughness. The results obtained showed a good correlation between the roughness critical exponent and the degree of malignancy of the tumor.

Research paper thumbnail of Fractal Properties and Critical Exponents for Tumor Staging and Classification

In general, tumors exhibit irregular borders with geometrical properties which are expected to de... more In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image to clearly define the active region of the tumor and its border. In the present work, T1 and T2 weighted magnetic resonance images of brain tumors were used to construct a nosologic map using in vivo magnetic resonance spectroscopy and biopsy for tissue classification and reference tumor staging. Different segmentation procedures were performed on the images, including gray level threshold and deformable contours (snakes). Several fractal properties were determined on the contour: the capacity or fractal dimension and the correlation dimension for different time series constructed from the original contour. Also a critical exponent coming from the contour roughness was calculated. The results obtained showed a good correlation between the rou...

Research paper thumbnail of Deformable Models (Snakes) for Fractal Analysis of Brain Tumors on T2-Weighted Images

Premature detection and classification for a disease process, is one of the most important object... more Premature detection and classification for a disease process, is one of the most important objectives for a physician. In reference to the brain, MRI can detect abnormal structures from the early stages of development, showing the morphological characteristics of neoplasic tissue, specifically the presence of rugosity or irregularities on its boundaries.

Research paper thumbnail of Diseño, Construcción y Puesta a Punto de un Tomógrafo por Ultrasonido para la Reconstrucción de Imágenes en 2D

En este trabajo se presenta el diseño, la construcción y la puesta a punto de un primer prototipo... more En este trabajo se presenta el diseño, la construcción y la puesta a punto de un primer prototipo de tomógrafo ultrasónico por transmisión, con miras a su aplicación en el área de la física médica. Las imágenes obtenidas corresponden al plano axial del objeto de estudio por medio de técnicas de reconstrucción algebraicas (ART, del inglés "Algebraic Reconstruction Technique") y retroproyección filtrada. El laboratorio de soporte instrumental, propuso la construcción de este tomógrafo ultrasónico, por lo tanto el diseño y su construcción estan basados en los requerimientos exigidos por este laboratorio. También, facilitó la instrumentación y parte de los materiales empleados en la construcción, por lo que las dificultades relacionadas con, financiamiento, disponibilidad o construcción de partes mecánicas y electrónicas, dictaron pautas importantes en el diseño propuesto. Otra de las limitaciones implícitas en el desarrollo del trabajo lo constituyen el tiempo de dedicación y...

Research paper thumbnail of Detección de Bordes Tumorales Mediante Contornos Activos (Snake) y Caracterización Mediante Análisis de Series Temporales

Research paper thumbnail of Evaluation of malignancy in tumors of the central nervous system using fractal dimension

In this work, we propose the use of the concepts of Fractal Dimension and Digital Image Processin... more In this work, we propose the use of the concepts of Fractal Dimension and Digital Image Processing, as a possible methodology to characterize the degree of malignancy of neoplastic structures located in the Central Nervous System. The images were detected by Magnetic Resonance Imaging (MRI) techniques including Proton Density, T 1 , and T 2 images. Malignant lesions (Gliomas) were compared with benign ones (Cysts). The Correlation Dimension, Lyapunov Exponents and Information Dimension were used as the relevant geometrical properties to characterize the irregular edge present in a particular structure. The edge was obtained by means of an edge detector operator and afterwards a codification procedure based on Fourier Descriptors was used to generate a numerical array or Time Series. The analysis of the processed images revealed that the relevant geometrical properties exhibit a different behavior in the case of gliomas compared to cystic lesions, a fact that can be used by the physician as an auxiliary tool to evaluate the malignancy of neoplastic structures in the brain.

Research paper thumbnail of Prototype of Stereoscopic Vision System to Improve the Image Quality in Turbid Waters during Underwater Inspections

OCEANS 2006, 2006

Underwater Visual Inspection is one of the main Non-Destructive Testing (NDT) techniques that can... more Underwater Visual Inspection is one of the main Non-Destructive Testing (NDT) techniques that can give us an accurate idea of the condition of any structure placed underwater. However, water and everything within affect light, compromising vision acuity and Inspector judgement. This work explores the possibility to compensate the side effects that light reflection and scattering (caused by turbidity) produce in

Research paper thumbnail of Glasslike ultrasonic properties of Dominican amber above helium temperatures

Journal of Applied Physics, 1991

ABSTRACT Measurements of the ultrasonic attenuation and relative velocity changes of longitudinal... more ABSTRACT Measurements of the ultrasonic attenuation and relative velocity changes of longitudinal waves of frequencies between 5 and 25 MHz are reported for clear yellow Dominican amber at low temperatures. Between 4 and 130 K the attenuation and velocity change are glasslike in their temperature and frequency dependencies. At higher temperatures both properties seemed to be affected by the α or β viscoelastic relaxations. Similar ultrasonic behavior is reported for commercial polymethylmethacrylate. Our results at low temperatures compare well quantitatively with data of other organic and inorganic glasses, except for the stronger logarithmic frequency‐dependent velocity change which is observed for both materials.

Research paper thumbnail of Multi-coil eddy current anisotropy detection probe

NDT & E International, 1995

Research paper thumbnail of Viscoelastic relaxation at megahertz frequencies in a Guasare (Venezuela) coal

Fuel, 1994

Ultrasonic attenuation and the fractional sound velocity shift for propagation parallel to beddin... more Ultrasonic attenuation and the fractional sound velocity shift for propagation parallel to bedding planes have been measured from liquid helium at room temperature in low-rank coal of south American origin in the frequency range 4 to 25 MHz. A previously unreported strong δ-...

Research paper thumbnail of Fractal Analysis of Tumoral Lesions in Brain

In this work, it is proposed a method for supervised characterization and classification of tumor... more In this work, it is proposed a method for supervised characterization and classification of tumoral lesions in brain, based on the analysis of irregularities at the lesion contour on T2-weighted MR images. After the choice of a specific image, a segmentation procedure with a threshold selected from the histogram of intensity levels is applied to isolate the lesion, the contour is detected through the application of a gradient operator followed by a conversion to a ";time series"; using a chain code procedure. The correlation dimension is calculated and analyzed to discriminate between normal or malignant structures. The results found showed that it is possible to detect a differentiation between benign (cysts) and malignant (gliomas) lesions suggesting the potential of this method as a diagnostic tool.