Procesamiento de Señales e Imágenes Digitales.
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Item Soft tissue characterization using different quantitative ultrasound modalities(Pontificia Universidad Católica del Perú, 2019-10-24) Romero Gutierrez, Stefano Enrique; Castañeda Aphan, Benjamín; Lavarello Montero, Roberto JannielQuantitative ultrasound has been used in several modalities for different experiments such as simulated phantom, physical phantoms, ex vivo and in vivo tissues. The potential of the ultrasound techniques could be useful to complemented medical diagnosis. In this work, two quantitative ultrasound techniques are applied on in vivo experiments: crawling waves sonoelastography applied to bicep brachii and a regularized power law for backscattering and attenuation coefficient for ovary tumor. A crawling waves sonoelastography (CWS) method was applied using two mini-shakers making parallel contact (conventional setup) and normal contact with the surface in two phantoms (homogeneous and inhomogeneous) using the phase derivative algorithm to assess the performance of the normal excitation with well-know metrics such as error, coefficient of variation, signal-to noise ratio and contrast-to noise ratio. The results suggest that the normal excitation provides comparable stiffness estimation in homogeneous and inhomogeneous phantoms. For in vivo test, a bicep barchii from healthy volunteers were assess in two experiments: relaxed-contracted and with a range weight of load. The application of normal setup indicated that a measurement of the relative stiffness on bicep brachii can be realized. The results indicated that a using the incremental weight causes a increase on the stiffness of the bicep following a linear behavior. A regularized power law (RPL) method was implemented and testing with simulated phantoms using a combination of the possible variables of data block size and the regularized parameters of the three variables of the backscattering and attenuation coefficients. The results showed that is possible provide accurate and precise backscattering and attenuation coefficient in the same algorithm. Additionally, in vivo breast experiments was performed and compared with the literature obtaining comparable results. Finally, a tumor of patients with suspected ovarian cancer were assess. The results suggests that RPL method and in general provides reasonable depictions of the reflectivity and attenuation of interrogated media.Item Characterization of healthy skin with high-frequency ultrasound using quantitative ultrasound(Pontificia Universidad Católica del Perú, 2018-08-20) Saavedra Bazán, Ana Cecilia; Castañeda Aphan, BenjamínThe skin is the largest organ of the body that protects it from the external environment. High- frequency ultra sound (HF-US) has been used to visualize the skin in depth and to diagnose some pathologies in dermatological applications. Quantitative ultrasound (QUS) includes several techniques that provide values of particular physical properties. In this thesis work, three QUS parameters are explained and used to characterize healthy skin through HF-US: attenuation coefficient slope (ACS), backscatter coefficient (BSC) and shear wave speed (SWS). They were estimated with the regularized spectral-log difference (RSLD) method, the reference phan- tom method, and the crawling wave sonoelastography method, respectively. All the three parameters were assessed in phantoms, ex vivo and in vivo skin. In calibrated phantoms, RSLD showed a reduc- tion of up to 93% of the standard deviation concerning the estimation with SLD, and BSC showed an agreement with the Faran’s theoretical curve. In gelatin-based phantoms, surface acoustic waves (SAWs) were estimated in two interfaces: solid-water and solid-US gel, which all owed corroborating SAWs presence and finding an empirical compensation factor when the coupling interface is US gel. A correction factor of 0:97 for SAW-to-shear was found to avoid underestimation in phantoms. Porcine thigh was calculated in the range from 8 to 27 MHz, where the ACS was 4:08 _+_0:43 dB cm -1 MHz-1 and BSC was in the range from 10 1 to 10° sr-1 _cm-1. Crawling wave sonoelastography method was applied for the vibration frequencies between 200 Hz and 800 Hz, where SWS was in the range from 4:6 m/sto9:1 m/s. In vivo ACS and BSC were assessed in the healthy forearm and thigh, whereas SWS only in the thigh. The average ACS in the forearm dermis was 2.07dB cm-1 _MHz-1, which is in close agreement with the literature. A significant difference (p < 0.05) was found between the ACS in the forearm dermis and the thigh dermis (average ACS of 2.54dB cm-1 _MHz-1). The BSC of the forearm and thigh dermis were in the range from 10 -1 to 10° sr-1 _cm-1, and in the range from 10-1 to 10° sr-1 _cm-1, respectively. The SWS in the thigh dermis was 2:4 _+_0:38 m/s for a vibration frequency of 200Hz, with an increasing trend as frequency increases. Results suggest that these QUS parameters have the potential to be used as a tool for in vivo skin characterization and show potential for future application in skin lesions.Item Evaluation of Elastographic techniques generated by means of external vibration(Pontificia Universidad Católica del Perú, 2017-12-01) Arroyo Barboza, Johnny Junior; Castañeda Aphan, Benjamín; Salcudean, TimBreast cancer is one of the greatest problems of national and international public health, whose incidence among women population shows an increasing trend. Nowadays there are several elastographic techniques, which seek to characterize the tissue, that is, to analyze the response produced by the application of a perturbation in the medium, to describe its mechanical properties. Among the modalities used are ultrasound, nuclear magnetic resonance and optical coherence tomography. On the other hand, among the types of disturbance used are low frequency mechanical waves, a uniform compression force or acoustic radiation force. In this thesis work, ultrasound was used due to its low economical cost in comparison to the other modalities. In addition, the type of perturbation selected was the external mechanical vibration, as it ensures the achievement of quantitative results, there is no risk of temperature rise in the analyzed area and allows the repeatability of the results obtained. Hence, two elastographic techniques were the axes of the present work: vibro-elastography and normal vibration holography. For the first, a calibrated phantom and a gelatin-based phantom were used, in order to characterize and validate the technique over a wide range of excitation frequencies. Posteriorly, 18 patients were analyzed prior biopsy exam, obtaining elastograms and contrasting them with the respective biopsy results. The results suggest that the technique is able to identify the presence of benign or malignant cancer, and the elasticity estimated agree with values reported in the literature. The second technique is proposed in the elastography field for the first time. Based on holography, its experimental scheme is established, and the mathematical expression for shear speed estimation is presented. Results from simulation and experiments performed on homogeneous and heterogeneous phantoms are presented, and the estimates are compared with previously obtained reference values. The results suggest that the estimates are close to the reference values for all media tested, and the technique must be studied in depth to revert artifacts formation.Item 3D reconstruction of chronic wounds using a hand-held camcorder and its application in cutaneous leishmaniasis wounds(Pontificia Universidad Católica del Perú, 2017-03-09) Casas Guido, Eda Leslie Mónica; Castañeda Aphan, BenjamínChronic wounds are a major healthcare problem worldwide which mainly a ects geriatric population and patients with limited mobility. In tropical countries, Cutaneous Leishmaniasis (CL) is also a cause for chronic wounds, being endemic in 75% of Peru . In this context, the assessment of these type of wounds represents a big challenge due to the limited access to specialized medical resources. This work aims to develop a video-based method to compute the 3D point cloud of skin wounds which could provide accurate metrics for medical assessment despite of the location of the patient. Recently, CL specialists have used metrics as volume in clinical assessment with promising results. The acquisition protocol is prompt to be user friendly and feasible in remote locations; the video is taken using a commercial hand-held video camera without a rig or special illumination. The algorithm follows the Structure from Motion methodology: FAST feature detector, pyramidal optical flow and Jacob’s method for missing points estimation. The results show good performance in terms of accuracy and repeatability of the point cloud computation, less than 0.6 mm and 0.21 mm respectively. However, experiments suggest that the volume computation technique does not adapt well to the proposed method output and requires a deeper analysis. The method has been entirely implemented using open source libraries.Item Evaluation of shear wave speed measurements using crawling waves sonoelastography and single tracking location acoustic radiation force impulse imaging(Pontificia Universidad Católica del Perú, 2015-07-25) Ormachea Quispe, Juvenal; Castañeda Aphan, Benjamín; Parker, Kevin J.Many pathological conditions are closely related with an increase in tissue sti ness. For many years, experts performed manual palpation in order to measure elasticity changes, however, this method can only be applied on superficial areas of the human body and provides crude sti ness estimation. Elastography is a technique that attempts to characterize the elastic properties of tissue in order to provide additional and useful information for clinical diagnosis. For more than twenty years, di erent research groups have developed various elastography modalities with a strong interest for quantitative images during the last decade. Recently, comparative studies among di erent elastographic techniques have been performed in order to better characterize biomaterials, to cross-validate several shear wave elastographic modalities and to study the factors that influence their precision and accuracy. This comparison works may contribute to achieve standardization in quantitative elastography and their use in commercial equipment for their application in human patients. However, there is still a limited literature in the field of quantitative elastography modalities comparisons. This thesis focuses on the comparison between two elastographic techniques: crawling wave sonoelastography (CWS) and single tracking location-acoustic radiation force impulse (STL-ARFI). The comparison shows the estimation of the shear wave speed (SWS), lateral resolution, contrast and contrast-to-noise ratio (CNR) in homogeneous and inhomogeneous phantoms using both techniques. The SWS values obtained with both modalities are validated with mechanical measurements that are considered as ground truth. The SWS results for the three di erent homogeneous phantoms (10%, 13%, and 16% gelatin concentrations), show good agreement between CWS, STL-ARFI and mechanical measurements as a function of frequency. The maximum accuracy errors obtained with CWS were 2.52%, 1.63% and 2.26%. For STL-ARFI, the maximum errors were 6.22%, 5.63% and 4.08% for the 10%,13% and 16% gelatin phantom respectively. For lateral resolution, contrast and CNR estimated in the inhomogeneous phantoms, it can be seen that for vibration frequencies higher than 340 Hz, CWS presents better results than the obtained with STL-ARFI using distances between the push beams ( x) higher than 4 mm. However, using these vibration frequencies will not be feasible for in vivo tissues due to attenuation problems. It that sense, for lower vibration frequencies than 300 Hz and x among 3 mm and 6 mm, comparable lateral resolution, contrast and CNR was obtained. Finally, the results of this study contribute to the data currently available for comparing elastographic techniques. Moreover, the methodology implemented in this document may be helpful for future standardization for di erent elastographic modalities.Item 3D updating of solid models based on local geometrical meshes applied to the reconstruction of ancient monumental structures(Pontificia Universidad Católica del Perú, 2014-10-14) Zvietcovich Zegarra, José Fernando; Castañeda Aphan, Benjamín; Perucchio, RenatoWe introduce a novel methodology for locally updating an existing 3D solid model of a complex monumental structure with the geometric information provided by a 3D mesh (point cloud) extracted from the digital survey of a specific sector of a monument. Solid models are fundamental for engineering analysis and conservation of monumental structures of the cultural heritage. Finite elements analysis (FEA), the most versatile and commonly used tool for the numerical simulation of the static and dynamic response of large structures, requires 3D solids which accurately represent the outside as well as the inside geometry and topology of the domain to be analyzed. However, the structural changes introduced during the lifetime of the monument and the damage caused by anthropogenic and natural factors contribute to producing complex geometrical configurations that may not be generated with the desired accuracy in standard CAD solid modeling software. On the other hand, the development of digital techniques for surveying historical buildings and cultural monuments, such as laser scanning and photogrammetric reconstruction, has made possible the creation of accurate 3D mesh models describing the geometry of those structures for multiple applications in heritage documentation, preservation, and archaeological interpretations. The proposed methodology consists of a series of procedures which utilize image processing, computer vision, and computational geometry algorithms operating on entities defined in the Solid Modeling space and the Mesh space. The operand solid model is defined as the existing solid model to be updated. The 3D mesh model containing new surface information is first aligned to the operand solid model via 3D registration and, subsequently, segmented and converted to a provisional solid model incorporating the features to be added or subtracted. Finally, provisional and operand models are combined and data is transferred through regularized Boolean operations performed in a standard CAD environment. We test the procedure on the Main Platform of the Huaca de la Luna, Trujillo, Peru, one of the most important massive earthen structures of the Moche civilization. Solid models are defined in AutoCAD while 3D meshes are recorded with a Faro Focus laser scanner. The results indicate that the proposed methodology is effective at transferring complex geometrical and topological features from the mesh to the solid modeling space. The methodology preserves, as much as possible, the initial accuracy of meshes on the geometry of the resultant solid model which would be highly difficult and time consuming using manual approaches.Item Desarrollo y comparación de diversos mapas de probabilidades en 3D del cáncer de próstata a partir de imágenes de histología(Pontificia Universidad Católica del Perú, 2013-12-04) Díaz Rojas, Kristians Edgardo; Castañeda Aphan, BenjamínUnderstanding the spatial distribution of prostate cancer and how it changes according to prostate specific antigen (PSA) values, Gleason score, and other clinical parameters may help comprehend the disease and increase the overall success rate of biopsies. This work aims to build 3D spatial distributions of prostate cancer and examine the extent and location of cancer as a function of independent clinical parameters. The border of the gland and cancerous regions from whole-mount histopathological images are used to reconstruct 3D models showing the localization of tumor. This process utilizes color segmentation and interpolation based on mathematical morphological distance. 58 glands are deformed into one prostate atlas using a combination of rigid, a ne, and b-spline deformable registration techniques. Spatial distribution is developed by counting the number of occurrences in a given position in 3D space from each registered prostate cancer. Finally a di erence between proportions is used to compare di erent spatial distributions. Results show that prostate cancer has a significant di erence (SD) in the right zone of the prostate between populations with PSA greater and less than 5 ng=ml. Age does not have any impact in the spatial distribution of the disease. Positive and negative capsule-penetrated cases show a SD in the right posterior zone. There is SD in almost all the glands between cases with tumors larger and smaller than 10% of the whole prostate. A larger database is needed to improve the statistical validity of the test. Finally, information from whole-mount histopathological images could provide better insight into prostate cancer.