Evaluation of shear wave speed measurements using crawling waves sonoelastography and single tracking location acoustic radiation force impulse imaging

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.Tesi

Estimación de áreas de heridas de Leishmaniasis por procesamiento digital de imágenes y su correlación con la evolución al tratamiento

La Leishmaniasis es una enfermedad parasitaria de difícil curación caracterizada por comprometer la piel, mucosas y vísceras. Actualmente, el Grupo de Estudios de Leishmaniasis (GEL) del Instituto de Medicina Tropical Alexander von Humboldt (IMTAvH) de la Universidad Peruana Cayetano Heredia (UPCH) evalúa la mejora del tratamiento de lesiones en la piel ocasionada por la Leishmaniasis cutánea (LC) mediante su categorización en estadíos. Como posible indicador de mejoría los médicos y personal especializado miden el área de la lesión aproximándola a una elipse y trazando el borde de la misma con una lámina transparente sobrepuesta a la superficie de la piel. Estos procedimientos presentan criterios subjetivos para su evaluación, ya que están basados en la experiencia de cada médico. Por tanto, la percepción de mejoría de la lesión presenta alta variabilidad según el médico encargado de la evaluación del tratamiento. En este documento se presenta la descripción de la enfermedad, así como una breve referencia al uso del procesamiento de imágenes aplicado a lesiones de piel y su comparación con métodos manuales. Se muestra la metodología aplicada para el reclutamiento, consentimiento y monitoreo de los pacientes y la metodología para la medición manual y automática. Se describe el proceso de adquisición de imágenes, los procedimientos para hallar el área en las mediciones manuales y las etapas del algoritmo automático para clasificar la lesión y estimar su área. Se indica la evolución del área de la lesión durante el tratamiento en distintos pacientes y se compara con los métodos manuales. Se calculó la variabilidad existente, se obtuvo resultados de hasta un 40% de variabilidad en mediciones manuales, una variabilidad alta para determinar con certeza el valor del área medida. Se mejoró el método de adquisición de imágenes propuesto por el Laboratorio de Imágenes Médicas-PUCP en una investigación previa (Ej. condiciones de iluminación). El algoritmo automático logra estimar el área de manera repetible y este puede ser comparable con los métodos manuales. De esta manera, se corrobora la factibilidad de uso de técnicas de procesamiento de imágenes para obtener el área de la lesión. En los pacientes que dieron su consentimiento para esta investigación, se halló el porcentaje de disminución del área de la lesión respecto al valor inicial, de esta forma, es factible ubicar la lesión en uno de los cinco estadíos propuestos por el GEL-UPCH. Finalmente, se recomienda seguir con la presente investigación haciendo el seguimiento a nuevos pacientes que presenten LC al menos al 95% del tiempo de tratamiento para lograr una validación médica. El área de piel infiltrada no pudo ser estimada debido a que su clasificación depende de la textura de la piel y no del color. Por tanto, se propone y recomienda utilizar alguna técnica de ultrasonido que pueda estimar la rigidez de la piel enferma, de esta manera, se pueda estimar el área para piel infiltrada.Tesi

Mejora de la gestión logística mediante la aplicación del modelo Scor para el proyecto Q’ewar en el distrito de Andahuaylillas, Cusco, 2019

El presente trabajo de investigación tiene por objetivo mejorar la gestión logística mediante la aplicación del modelo SCOR, en el proyecto Q’ewar en el distrito Andahuaylillas en la región Cusco en el año 2019. La investigación es de tipo aplicada, de nivel explicativo, con diseño pre experimental, con método hipotético-deductivo, de enfoque cuantitativo, las técnicas de recolección de datos utilizados han sido el análisis documental, la observación experimental, la encuesta y la entrevista; en tanto que los instrumentos han sido: el registro documental, la ficha de observación, el cuestionario y la guía de entrevista; la población y muestra de estudio estuvo conformado por los 45 colaboradores del proyecto. Las conclusiones permiten evidenciar que se obtuvo mejoras en la gestión logística con la aplicación del modelo SCOR en el proyecto Q’ewar. La cual es evidenciada en el análisis de los KPIs involucrados en el proceso. A pesar que la totalidad de los resultados serán vistos en el transcurso del proceso de implementación y adecuación del modelo para su re implementación, se obtuvo datos favorables cuantitativos y cualitativos de los procesos claves dentro de la gestión logística del proyecto, como son el proceso de planificación, compras, gestión de inventarios y despacho de productos.Tesi

Pulse-Echo Quantitative US Biomarkers for Liver Steatosis: Toward Technical Standardization

Excessive liver fat (steatosis) is now the most common cause of chronic liver disease worldwide and is an independent risk factor for cirrhosis and associated complications. Accurate and clinically useful diagnosis, risk stratification, prognostication, and therapy monitoring require accurate and reliable biomarker measurement at acceptable cost. This article describes a joint effort by the American Institute of Ultrasound in Medicine (AIUM) and the RSNA Quantitative Imaging Biomarkers Alliance (QIBA) to develop standards for clinical and technical validation of quantitative biomarkers for liver steatosis. The AIUM Liver Fat Quantification Task Force provides clinical guidance, while the RSNA QIBA Pulse-Echo Quantitative Ultrasound Biomarker Committee develops methods to measure biomarkers and reduce biomarker variability. In this article, the authors present the clinical need for quantitative imaging biomarkers of liver steatosis, review the current state of various imaging modalities, and describe the technical state of the art for three key liver steatosis pulse-echo quantitative US biomarkers: attenuation coefficient, backscatter coefficient, and speed of sound. Lastly, a perspective on current challenges and recommendations for clinical translation for each biomarker is offered

Viscoelastic tissue characterization based on harmonic and transient shear wave elastography

Thesis (Ph. D.)--University of Rochester. Department of Electrical and Computer Engineering, 2020.Elastography is a rapidly growing field in which imaging systems are used to estimate the viscoelastic properties of tissue. For example, elevated liver stiffness is an important indicator of fibrosis, and so the diagnostic value of elastography adds new information to the conventional radiology image. Within elastography techniques, shear waves play an important role, as they can be propagated by a source through the soft tissues and tracked by the imaging system. The distinction between shear wave group and phase velocities is important in elastography, because diagnoses are made using a variety of techniques on different scanners: some rely on group velocity estimates, but others assess phase velocity. This document reviews the general definitions of group and phase velocity and examines their specific relations within an important general class of rheological models. For the class of tissues and materials exhibiting power law dispersion, group velocity is significantly greater than phase velocity, and simple expressions are shown to interrelate the commonly measured parameters. Examples are given from phantoms and tissues. This thesis then considers the propagation of shear waves from acoustic radiation impulsive forces. Parameter estimation of the shear wave speed in tissues are based on some underlying models of shear wave propagation. The models typically include specific choices of the spatial and temporal shape of the force impulse and the elastic or viscoelastic properties of the medium. In this work, the analytical treatment of 2-D shear wave propagation in a biomaterial is presented. Estimators of attenuation and shear wave speed are derived from the analytical solutions, and these are applied to an elastic phantom, a viscoelastic phantom, and in vivo liver using a clinical ultrasound scanner. Additionally, it shows and examines the rheological models that can capture the dominant viscoelastic behaviors associated with fat and inflammation in the liver, and quantifies the resulting changes in shear wave speed and viscoelastic parameters. Theoretical results are shown to match measurements in phantoms and animal studies reported in the literature. Finally, the shear wave attenuation parameter, and its relation to diseased states of the liver, is studied. This work focused on the hypothesis that steatosis adds a viscous (lossy) component to the liver, which increases shear wave attenuation. Twenty patients’ livers were scanned and the resulting displacement profiles were analyzed to derive both the speed and attenuation of the shear waves within 6-cm2 regions of interest. The results were compared with pathology scores obtained from ultrasound-guided liver biopsies taken under ultrasound guidance. Across these cases, increases in shear wave attenuation were linked to increased steatosis score. This preliminary study supports the hypothesis and indicates the possible utility of the measurements for non-invasive and quantitative assessment of steatosis. The shear wave speed estimators can be relatively simple if plane wave behavior is assumed with a known direction of propagation as it is considered in several elastography methods based on acoustic radiation force impulse. However, multiple reflections from organ boundaries and internal inhomogeneities and mode conversions can create a complicated field in time and space. Thus, this work also explores the mathematics of multiple component shear wave fields and derives the basic properties. It approaches this problem from the historic perspective of reverberant fields, a conceptual framework used in architectural acoustics and related fields. The reverberant shear wave field approach was evaluated and compared with another well-known elastography technique using two calibrated elastic and viscoelastic phantoms. The results indicate that it is possible to estimate the viscoelastic properties in each scanned medium. Moreover, the simultaneous multi-frequency application can be accomplished by applying an array of external sources that can be excited by multiple frequencies within a bandwidth, all contributing to the shear wave field produced in the liver or other target organ. This enables the analysis of the dispersion of shear wave speed as it increases with frequency, indicating the viscoelastic and lossy nature of the tissue under study. Furthermore, complete 2-D dispersion images can be created and displayed alongside the shear wave speed images. The author reports preliminary studies on in vivo breast and liver tissues, employing frequencies up to 700 Hz in breast tissue, and robust reverberant patterns of shear waves across the entire liver and kidney in obese patients. Dispersion images are shown to have contrast between tissue types and with quantitative values that align with previous studies. In addition to the shear wave speed and dispersion, this thesis also reports, numerically and experimentally, that it is possible to assess shear wave attenuation in tissues by using a reverberant shear wave field. The shear wave attenuation coefficient results are in agreement with those obtained in previous studies reported in the literature. In that sense, the R-SWE approach shows the potential to obtain a complete rheological characterization in in vivo tissue by measuring the shear wave speed, shear wave dispersion, and shear wave attenuation. Finally, the specific conclusions of this research are summarized in the last chapter, with a special emphasis of next steps and future work that can be accomplished to improve the results presented in this work

Mejora de la gestión logística mediante la aplicación del modelo Scor para el proyecto Q’ewar en el distrito de Andahuaylillas, Cusco, 2019

TesisEl presente trabajo de investigación tiene por objetivo mejorar la gestión logística mediante la aplicación del modelo SCOR, en el proyecto Q’ewar en el distrito Andahuaylillas en la región Cusco en el año 2019. La investigación es de tipo aplicada, de nivel explicativo, con diseño pre experimental, con método hipotético-deductivo, de enfoque cuantitativo, las técnicas de recolección de datos utilizados han sido el análisis documental, la observación experimental, la encuesta y la entrevista; en tanto que los instrumentos han sido: el registro documental, la ficha de observación, el cuestionario y la guía de entrevista; la población y muestra de estudio estuvo conformado por los 45 colaboradores del proyecto. Las conclusiones permiten evidenciar que se obtuvo mejoras en la gestión logística con la aplicación del modelo SCOR en el proyecto Q’ewar. La cual es evidenciada en el análisis de los KPIs involucrados en el proceso. A pesar que la totalidad de los resultados serán vistos en el transcurso del proceso de implementación y adecuación del modelo para su re implementación, se obtuvo datos favorables cuantitativos y cualitativos de los procesos claves dentro de la gestión logística del proyecto, como son el proceso de planificación, compras, gestión de inventarios y despacho de productos

Validations of the Microchannel Flow Model for Characterizing Vascularized Tissues

The microchannel flow model postulates that stress-strain behavior in soft tissues is influenced by the time constants of fluid-filled vessels related to Poiseuille’s law. A consequence of this framework is that changes in fluid viscosity and changes in vessel diameter (through vasoconstriction) have a measurable effect on tissue stiffness. These influences are examined through the theory of the microchannel flow model. Then, the effects of viscosity and vasoconstriction are demonstrated in gelatin phantoms and in perfused tissues, respectively. We find good agreement between theory and experiments using both a simple model made from gelatin and from living, perfused, placental tissue in vitro

Plantar Soft Tissue Characterization Using Reverberant Shear Wave Elastography: A Proof-of-Concept Study

Plantar soft tissue stiffness provides relevant information on biomechanical characteristics of the foot. Therefore, appropriate monitoring of foot elasticity could be useful for diagnosis, treatment or health care of people with complex pathologies such as a diabetic foot. In this work, the reliability of reverberant shear wave elastography (RSWE) applied to plantar soft tissue was investigated. Shear wave speed (SWS) measurements were estimated at the plantar soft tissue at the first metatarsal head, the third metatarsal head and the heel from both feet in five healthy volunteers. Experiments were repeated for a test–retest analysis with and without the use of gel pad using a mechanical excitation frequency range between 400 and 600 Hz. Statistical analysis was performed to evaluate the reliability of the SWS estimations. In addition, the results were compared against those obtained with a commercially available shear wave-based elastography technique, supersonic imaging (SSI). The results indicate a low coefficient of variation for test–retest experiments with gel pad (median: 5.59%) and without gel pad (median: 5.83%). Additionally, the values of the SWS measurements increase at higher frequencies (median values: 2.11 m/s at 400 Hz, 2.16 m/s at 450 Hz, 2.24 m/s at 500 Hz, 2.21 m/s at 550 Hz and 2.31 m/s at 600 Hz), consistent with previous reports at lower frequencies. The SWSs at the plantar soft tissue at the first metatarsal head, third metatarsal head and heel were found be significantly (p<0.05) different, with median values of 2.42, 2.16 and 2.03 m/s, respectively which indicates the ability of the method to differentiate between shear wave speeds at different anatomical locations. The results indicated better elastographic signal-to-noise ratios with RSWE compared to SSI because of the artifacts presented in the SWS generation. These preliminary results indicate that the RSWE approach can be used to estimate the plantar soft tissue elasticity, which may have great potential to better evaluate changes in biomechanical characteristics of the foot