Procesamiento de Señales e Imágenes Digitales.

Permanent URI for this collectionhttp://98.81.228.127/handle/20.500.12404/5040

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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, Tim
Breast 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.
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 Janniel
Quantitative 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.