Quantitative Ultrasound (QUS) techniques with the advantages of an axial transmission measurement were applied to implement an ultrasonic system for cortical bone evaluation. This evaluation is focused on the measurement and characterization of shear waves propagating in the axial direction of the cortical layer of bone. Signals were analyzed in time and frequency domains. And, in order to understand the wave propagation phenomenon, and predict experimental results, simulations using the elastic Finite-difference-time-domain (FDTD) method were implemented considering isotropic and anisotropic bone models. Additionally, shear wave velocities using the axial method were verified by a simple thought transmission measurement. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

A osteoporose é uma doença que afeta o tecido ósseo sendo caracterizada principalmente pela diminuição da massa óssea e pela deterioração da arquitetura do osso. O método atualmente utilizado no diagnóstico da osteoporose é a densitometria óssea (DEXA -Dual Energy X-ray Absorptiometry), que utiliza radiação ionizante. Vários estudos têm sido publicados discutindo o uso de técnicas complementares ou alternativas à densitometria óssea. Uma dessas técnicas é a ultrasonometria, que é baseada na análise da propagação do ultra-som para identificar a qualidade do tecido ósseo. O objetivo desse trabalho é contribuir com o acréscimo de dados para a avaliação da possibilidade de uso dessa técnica como alternativa à técnica da densitometria óssea. Foi realizado um estudo de correlação entre medidas experimentais em ossos trabeculares de calcâneos humanos obtidas com o equipamento de ultrasonometria óssea SONOST-2000 (Vicmed/OsteoSys-MedisonÒ) e medidas de ensaio mecânico de compressão. A microscopia eletrônica de varredura foi utilizada como um teste complementar para identificar as modificações na microarquitetura das amostras de ossos humanos sadios e osteopênicos. Os resultados indicam que o BQI (Bone Quality Index – Índice de Qualidade Óssea) pode ser usado como um método indireto de averiguação das importantes propriedades na determinação do risco de fratura, como por exemplo, a tensão máxima suportada pelo material. / Osteoporosis is a disease that affects bone tissue and is characterized by a decrease in its mass and deterioration of its architeture. The current method used in osteoporosis diagnostic is bone densitometry (DEXA- Dual Energy X-ray Absorption), which utilizes ionizing radiation. Various studies have been published discussing alternatives or complimentary techniques to bone densitometry. One of these techniques is quantitative untrasound (QUS), which is based on the analysis of ultrasound spread through bone tissue to assess its quality. The objective of this work is to add more data to the discussion of this technique as an alternative to bone densitometry. Correlation studies between data from experiments in trabecular bones from the calcaneus of human cadavers have been performed using the quantitative ultrasound equipment SONOST-2000 (Vicmed/OsteoSys-Medison) and mechanical compression essays. Scanning Electron Microscopy was also used as an aid to identify modifications in the samples microarchiteture from health and osteopenic tissue. The results indicate that BQI (Bone Quality Index ) can be used as indirect method to obtain important parameters used in the assessment of fracture risk, such as the maximum load supported by the material.

A caracterização de tecido ósseo por ultra-som para o diagnóstico de osteoporose tem sido investigada como uma alternativa a densitometria óssea baseada em radiação ionizante. A interação do ultra-som com o tecido ósseo é fundamentalmente diferente da que ocorre com a energia ionizante. O potencial da técnica ultra-sônica baseia-se nos efeitos sobre a propagação do campo acústico causados pela estrutura, composição e massa do tecido que está sendo investigado. Quatro estudos in-vitro e um estudo clínico estão descritos neste trabalho. O primeiro estudo in-vitro compara a correlação entre medidas ultra-sônicas e de densidade mineral óssea (em g/cm3) em tecido trabecular humano e bovino. A velocidade e atenuação ultra-sônicas em amostras ósseas foram determinadas pela técnica de inserção convencional (modo de transmissão) e a medida de densidade mineral óssea foi realizada por absortometria de um fóton (SPA). O mecanismo de interação do ultra-som com osso trabecular é pouco conhecido. O segundo estudo in-vitro investigou como a presença da medula óssea afeta as medidas de velocidade e atenuação. As correlações entre medidas ultrasônicas e de densidade mineral óssea (em g/cm3) por SPA, com e sem a presença da medula óssea, são também determinadas. A medida ultra-sônica de inserção convencional é comparada a medida de inserção por contato. O terceiro estudo in-vitro investigou em amostras de calcâneo as correlações entre medidas ultra-sônicas e de densidade mineral óssea (em g/cm3 e em g/cm2) por SPA. A determinação da densidade mineral Óssea em g/cm2 (BMD) a partir de medidas ultra-sônicas nas amostras foi pela primeira vez investigada, utilizando-se uma técnica de regressão linear univariável e multivariável e uma técnica multivariável não-linear baseada em redes neurais. Um novo parâmetro, baseado na média da frequência instantânea (MIF) do sinal da amostra e de referência, foi proposto para caracterizar o tecido ósseo devido a sua alta correlação com a atenuação. O efeito das corticais ósseas do calcâneo nas medidas ultra-sônicas é pouco conhecido. O quarto estudo in-vitro determinou a correlação entre medidas ultrasônicas e de densidade mineral óssea (em g/cm3) por SPA, com e sem a presença das corticais ósseas. Finalmente, no estudo clínico foram determinadas as correlações entre medidas ultra-sônicas no calcanhar e de densidade mineral óssea por DEXA (em g/cm2) no cólo femoral. A determinação da densidade óssea a partir de medidas ultra-sônicas no calcanhar foi pela primeira vez investigada, utilizando-se uma técnica de regressão linear univariável e multivariável e uma técnica multivariável não-linear baseada em redes neurais. / Ultrasonic assessment of bone for managing osteoporosis has been investigated as an alternative to radition-based bone densitometry technology. In contrast with the ionizing electromagnetic radiation of such clinical bone densitometric technique, ultrasound is a mechanical wave and thus interacts with bone in a fundamentally distinct manner. Ultrasound is viewed as having great potential for assessing bone since its propagation is affected by the structure, composition, and mass of the bone tissue being interrogated. Four in-vitro and one clinical study are reported in this work. In the first in-vitro study a comparison is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and attenuation were evaluated through a standard transmission insertion technique and correlated with bone mineral density (in g/cm3 ) as determined with single photon absorptiometry (SPA). There is a relatively limited understanding of how ultrasound interacts with cancellous bone. One potentially model leads analytically to the demonstration that ultrasound propagation through bone is dependent on several factors, including the properties of the fluid, which saturates the pores of the cancellous bone tissue. The second in-vitro study was carried out to assess how the presence of marrow affects the velocity and attenuation measurements. The correlation between ultrasonic and densitometric measurements (in g/cm3) by SPA, with and without the bone marrow, are also determined. A second part of this study compared the measurements of ultrasonic attenuation and velocity on bovine cancellous bone samples using a standard insertion technique with those obtained using a contac method. The thrid in-vitro study with the calcis trabecular samples investigated the correlations between ultrasonic measurements and bone mineral density (in g/cm3 e em g/cm2) as measured by SPA. A nonlinear multivariate estimation technique based on neural network was the first time investigated to determine the ability of ultrasonic measurements to estimate bone mineral density in g/cm2 (BMD). A linear univariate and multivariate estimation of BMD was compared with the neural network approach. A new parameter to characterize the trabecular bone is been proposed, which is based on the mean instantaneous frequency (MIF) of the sample and reference signals after transmission through the os calcis. It was founded a high correlation between MIF and the attenuation (BUA). Little is known about the effect of the os calcis cortical shell on ultrasonic measurements. The fourth in-vitro study with os calcis samples determined the correlation between ultrasonic and densitometric measurements (in g/cm3) by SPA with and without the cortical shell. Finally, a nonlinear multivariate estimation technique based on neural network was the first time investigated to determine the ability of clinical ultrasonic measurements in the heel to estimate bone mineral density (BMD) in the femoral neck. A linear univariate and multivariate estimation to predict BMD in patients is also compared with the neural network approach.

A caracterização de tecido ósseo por ultra-som para o diagnóstico de osteoporose tem sido investigada como uma alternativa a densitometria óssea baseada em radiação ionizante. A interação do ultra-som com o tecido ósseo é fundamentalmente diferente da que ocorre com a energia ionizante. O potencial da técnica ultra-sônica baseia-se nos efeitos sobre a propagação do campo acústico causados pela estrutura, composição e massa do tecido que está sendo investigado. Quatro estudos in-vitro e um estudo clínico estão descritos neste trabalho. O primeiro estudo in-vitro compara a correlação entre medidas ultra-sônicas e de densidade mineral óssea (em g/cm3) em tecido trabecular humano e bovino. A velocidade e atenuação ultra-sônicas em amostras ósseas foram determinadas pela técnica de inserção convencional (modo de transmissão) e a medida de densidade mineral óssea foi realizada por absortometria de um fóton (SPA). O mecanismo de interação do ultra-som com osso trabecular é pouco conhecido. O segundo estudo in-vitro investigou como a presença da medula óssea afeta as medidas de velocidade e atenuação. As correlações entre medidas ultrasônicas e de densidade mineral óssea (em g/cm3) por SPA, com e sem a presença da medula óssea, são também determinadas. A medida ultra-sônica de inserção convencional é comparada a medida de inserção por contato. O terceiro estudo in-vitro investigou em amostras de calcâneo as correlações entre medidas ultra-sônicas e de densidade mineral óssea (em g/cm3 e em g/cm2) por SPA. A determinação da densidade mineral Óssea em g/cm2 (BMD) a partir de medidas ultra-sônicas nas amostras foi pela primeira vez investigada, utilizando-se uma técnica de regressão linear univariável e multivariável e uma técnica multivariável não-linear baseada em redes neurais. Um novo parâmetro, baseado na média da frequência instantânea (MIF) do sinal da amostra e de referência, foi proposto para caracterizar o tecido ósseo devido a sua alta correlação com a atenuação. O efeito das corticais ósseas do calcâneo nas medidas ultra-sônicas é pouco conhecido. O quarto estudo in-vitro determinou a correlação entre medidas ultrasônicas e de densidade mineral óssea (em g/cm3) por SPA, com e sem a presença das corticais ósseas. Finalmente, no estudo clínico foram determinadas as correlações entre medidas ultra-sônicas no calcanhar e de densidade mineral óssea por DEXA (em g/cm2) no cólo femoral. A determinação da densidade óssea a partir de medidas ultra-sônicas no calcanhar foi pela primeira vez investigada, utilizando-se uma técnica de regressão linear univariável e multivariável e uma técnica multivariável não-linear baseada em redes neurais. / Ultrasonic assessment of bone for managing osteoporosis has been investigated as an alternative to radition-based bone densitometry technology. In contrast with the ionizing electromagnetic radiation of such clinical bone densitometric technique, ultrasound is a mechanical wave and thus interacts with bone in a fundamentally distinct manner. Ultrasound is viewed as having great potential for assessing bone since its propagation is affected by the structure, composition, and mass of the bone tissue being interrogated. Four in-vitro and one clinical study are reported in this work. In the first in-vitro study a comparison is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and attenuation were evaluated through a standard transmission insertion technique and correlated with bone mineral density (in g/cm3 ) as determined with single photon absorptiometry (SPA). There is a relatively limited understanding of how ultrasound interacts with cancellous bone. One potentially model leads analytically to the demonstration that ultrasound propagation through bone is dependent on several factors, including the properties of the fluid, which saturates the pores of the cancellous bone tissue. The second in-vitro study was carried out to assess how the presence of marrow affects the velocity and attenuation measurements. The correlation between ultrasonic and densitometric measurements (in g/cm3) by SPA, with and without the bone marrow, are also determined. A second part of this study compared the measurements of ultrasonic attenuation and velocity on bovine cancellous bone samples using a standard insertion technique with those obtained using a contac method. The thrid in-vitro study with the calcis trabecular samples investigated the correlations between ultrasonic measurements and bone mineral density (in g/cm3 e em g/cm2) as measured by SPA. A nonlinear multivariate estimation technique based on neural network was the first time investigated to determine the ability of ultrasonic measurements to estimate bone mineral density in g/cm2 (BMD). A linear univariate and multivariate estimation of BMD was compared with the neural network approach. A new parameter to characterize the trabecular bone is been proposed, which is based on the mean instantaneous frequency (MIF) of the sample and reference signals after transmission through the os calcis. It was founded a high correlation between MIF and the attenuation (BUA). Little is known about the effect of the os calcis cortical shell on ultrasonic measurements. The fourth in-vitro study with os calcis samples determined the correlation between ultrasonic and densitometric measurements (in g/cm3) by SPA with and without the cortical shell. Finally, a nonlinear multivariate estimation technique based on neural network was the first time investigated to determine the ability of clinical ultrasonic measurements in the heel to estimate bone mineral density (BMD) in the femoral neck. A linear univariate and multivariate estimation to predict BMD in patients is also compared with the neural network approach.

A osteoporose é uma doença que afeta o tecido ósseo sendo caracterizada principalmente pela diminuição da massa óssea e pela deterioração da arquitetura do osso. O método atualmente utilizado no diagnóstico da osteoporose é a densitometria óssea (DEXA -Dual Energy X-ray Absorptiometry), que utiliza radiação ionizante. Vários estudos têm sido publicados discutindo o uso de técnicas complementares ou alternativas à densitometria óssea. Uma dessas técnicas é a ultrasonometria, que é baseada na análise da propagação do ultra-som para identificar a qualidade do tecido ósseo. O objetivo desse trabalho é contribuir com o acréscimo de dados para a avaliação da possibilidade de uso dessa técnica como alternativa à técnica da densitometria óssea. Foi realizado um estudo de correlação entre medidas experimentais em ossos trabeculares de calcâneos humanos obtidas com o equipamento de ultrasonometria óssea SONOST-2000 (Vicmed/OsteoSys-MedisonÒ) e medidas de ensaio mecânico de compressão. A microscopia eletrônica de varredura foi utilizada como um teste complementar para identificar as modificações na microarquitetura das amostras de ossos humanos sadios e osteopênicos. Os resultados indicam que o BQI (Bone Quality Index – Índice de Qualidade Óssea) pode ser usado como um método indireto de averiguação das importantes propriedades na determinação do risco de fratura, como por exemplo, a tensão máxima suportada pelo material. / Osteoporosis is a disease that affects bone tissue and is characterized by a decrease in its mass and deterioration of its architeture. The current method used in osteoporosis diagnostic is bone densitometry (DEXA- Dual Energy X-ray Absorption), which utilizes ionizing radiation. Various studies have been published discussing alternatives or complimentary techniques to bone densitometry. One of these techniques is quantitative untrasound (QUS), which is based on the analysis of ultrasound spread through bone tissue to assess its quality. The objective of this work is to add more data to the discussion of this technique as an alternative to bone densitometry. Correlation studies between data from experiments in trabecular bones from the calcaneus of human cadavers have been performed using the quantitative ultrasound equipment SONOST-2000 (Vicmed/OsteoSys-Medison) and mechanical compression essays. Scanning Electron Microscopy was also used as an aid to identify modifications in the samples microarchiteture from health and osteopenic tissue. The results indicate that BQI (Bone Quality Index ) can be used as indirect method to obtain important parameters used in the assessment of fracture risk, such as the maximum load supported by the material.

Afin d'accélérer et automatiser l'analyse par ultrasons quantitatifs de ganglions lymphatiques de patients atteints d'un cancer, plusieurs segmentations automatiques des trois milieux rencontrés (le parenchyme du ganglion, la graisse périnodale et le sérum physiologique) sont étudiées. Une analyse statistique du signal d'enveloppe a permis d'identifier la distribution gamma comme le meilleur compromis en termes de qualité de la modélisation, simplicité du modèle et rapidité de l'estimation des paramètres. Deux nouvelles méthodes de segmentation basées sur l'approche par ensemble de niveaux et la distribution gamma sont décrites. Des statistiques locales du signal d'enveloppe permettent de tenir compte des inhomogénéités du signal dues à l'atténuation et la focalisation des ultrasons. La méthode appelée LRGDF modélise les statistiques du speckle dans des régions dont la taille est contrôlable par une fonction lisse à support compact. La seconde, appelée STS-LS, considère des coupes transverses, perpendiculaires au faisceau, pour gagner en efficacité. Une troisième méthode basée sur la classification par forêt aléatoire a été conçue pour initialiser et accélérer les deux précédentes. Ces méthodes automatiques sont comparées à une segmentation manuelle effectuée par un expert. Elles fournissent des résultats satisfaisants aussi bien sur des données simulées que sur des données acquises sur des ganglions lymphatiques de patients atteints d'un cancer colorectal ou du sein. Les paramètres ultrasonores quantitatifs estimés après segmentation automatique ou après segmentation manuelle par un expert sont comparables. / This work investigates approaches to obtain automatic segmentation of three media (i.e., lymph node parenchyma, perinodal fat and normal saline) in lymph node (LN) envelope data to expedite quantitative ultrasound (QUS) in dissected LNs from cancer patients. A statistical modeling study identified a two-parameter gamma distribution as the best model for data from the three media based on its high fitting accuracy, its analytically less-complex probability density function (PDF), and closed-form expressions for its parameter estimation. Two novel level-set segmentation methods that made use of localized statistics of envelope data to handle data inhomogeneities caused by attenuation and focusing effects were developed. The first, local region-based gamma distribution fitting (LRGDF), employed the gamma PDFs to model speckle statistics of envelope data in local regions at a controllable scale using a smooth function with a compact support. The second, statistical transverse-slice-based level-set (STS-LS), used gamma PDFs to locally model speckle statistics in consecutive transverse slices. A novel method was then designed and evaluated to automatically initialize the LRGDF and STS-LS methods using random forest classification with new proposed features. Methods developed in this research provided accurate, automatic and efficient segmentation results on simulated envelope data and data acquired for LNs from colorectal- and breast-cancer patients as compared with manual expert segmentation. Results also demonstrated that accurate QUS estimates are maintained when automatic segmentation is applied to evaluate excised LN data.

Dans le contexte de la caractérisation des tissus mammaires, on peut se demander ce que l’examen d’un attribut en échographie quantitative (« quantitative ultrasound » - QUS) d’un milieu diffusant (tel un tissu biologique mou) pendant la propagation d’une onde de cisaillement ajoute à son pouvoir discriminant. Ce travail présente une étude du comportement variable temporel de trois paramètres statistiques (l’intensité moyenne, le paramètre de structure et le paramètre de regroupement des diffuseurs) d’un modèle général pour l’enveloppe écho de l’onde ultrasonore rétrodiffusée (c.-à-d., la K-distribution homodyne) sous la propagation des ondes de cisaillement. Des ondes de cisaillement transitoires ont été générés en utilisant la mèthode d’ imagerie de cisaillement supersonique ( «supersonic shear imaging » - SSI) dans trois fantômes in-vitro macroscopiquement homogènes imitant le sein avec des propriétés mécaniques différentes, et deux fantômes ex-vivo hétérogénes avec tumeurs de souris incluses dans un milieu environnant d’agargélatine. Une comparaison de l’étendue des trois paramètres de la K-distribution homodyne avec et sans propagation d’ondes de cisaillement a montré que les paramètres étaient significativement (p < 0,001) affectès par la propagation d’ondes de cisaillement dans les expériences in-vitro et ex-vivo. Les résultats ont également démontré que la plage dynamique des paramétres statistiques au cours de la propagation des ondes de cisaillement peut aider à discriminer (avec p < 0,001) les trois fantômes homogènes in-vitro les uns des autres, ainsi que les tumeurs de souris de leur milieu environnant dans les fantômes hétérogénes ex-vivo. De plus, un modéle de régression linéaire a été appliqué pour corréler la plage de l’intensité moyenne sous la propagation des ondes de cisaillement avec l’amplitude maximale de déplacement du « speckle » ultrasonore. La régression linéaire obtenue a été significative : fantômes in vitro : R2 = 0.98, p < 0,001 ; tumeurs ex-vivo : R2 = 0,56, p = 0,013 ; milieu environnant ex-vivo : R2 = 0,59, p = 0,009. En revanche, la régression linéaire n’a pas été aussi significative entre l’intensité moyenne sans propagation d’ondes de cisaillement et les propriétés mécaniques du milieu : fantômes in vitro : R2 = 0,07, p = 0,328, tumeurs ex-vivo : R2 = 0,55, p = 0,022 ; milieu environnant ex-vivo : R2 = 0,45, p = 0,047. Cette nouvelle approche peut fournir des informations supplémentaires à l’échographie quantitative statistique traditionnellement réalisée dans un cadre statique (c.-à-d., sans propagation d’ondes de cisaillement), par exemple, dans le contexte de l’imagerie ultrasonore en vue de la classification du cancer du sein. / In the context of breast tissue characterization, one may wonder what the consideration of a quantitative ultrasound (QUS) feature of a scattering medium (such as a soft biological tissue) under propagation of a shear wave adds to its discriminant power. This work presents a study of the time varying behavior of three statistical parameters (the mean intensity, the structure parameter and the clustering parameter of scatterers) of a general model for the ultrasound backscattering echo envelope (i.e., the homodyned K-distribution) under shear wave propagation. Transient shear waves were generated using the supersonic shear imaging (SSI) method in three in-vitro macroscopically homogenous breast mimicking phantoms with different mechanical properties, and two ex-vivo heterogeneous phantoms with mice tumors included in an agar gelatin surrounding medium. A comparison of the range of the three homodyned K-distribution parameters with and without shear wave propagation showed that the parameters were significantly (p < 0.001) affected by shear wave propagation in the in-vitro and ex-vivo experiments. The results also demonstrated that the dynamic range of the statistical parameters during shear wave propagation may help discriminate (with p < 0.001) the three in-vitro homogenous phantoms from each other, and also the mice tumors from their surrounding medium in the ex-vivo heterogeneous phantoms. Furthermore, a linear regression model was applied to relate the range of the mean intensity under shear wave propagation with the maximum displacement amplitude of speckle. The linear regression was found to be significant : in-vitro phantoms : R2 = 0.98, p < 0.001 ; ex-vivo tumors : R2 = 0.56, p = 0.013 ; ex-vivo surrounding medium : R2 = 0.59, p = 0.009. In contrast, the linear regression was not as significant between the mean intensity without shear wave propagation and mechanical properties of the medium : in-vitro phantoms : R2 = 0.07, p = 0.328, ex-vivo tumors : R2 =0.55, p = 0.022 ; ex-vivo surrounding medium : R2 = 0.45, p = 0.047. This novel approach may provide additional information to statistical QUS traditionally performed in a static framework (i.e., without shear wave propagation), for instance, in the context of ultrasound imaging for breast cancer classification.

Ce travail de thèse porte sur l’analyse et le traitement des signaux ultrasonores pour la caractérisation de l’os cortical. La première partie est dédiée à l’analyse des signaux acquis par un prototype de sonde de transmission axiale à 1 MHz. Nous montrons qu’une contribution arrivant après le premier signal présente un intérêt pour la caractérisation ultrasonore de l’os cortical. En effet, cette contribution évaluée sur des radius humains in vitro est associée à une onde de flexion propagée dans l’os qui est dépendante de l’épaisseur corticale. L’analyse de cette contribution a nécessité le développement d’une technique de séparation d’ondes. Cette contribution étant plus basse fréquence que le premier signal et associée à un mode de propagation différent, nous montrons ainsi qu’une analyse plus poussée du signal peut permettre une approche multi-modes/multi-fréquences. Dans une seconde partie, nous montrons l’intérêt de l’évaluation de l’atténuation ultrasonore pour la caractérisation de l’os cortical. Lors d’une étude expérimentale in vitro sur des échantillons corticaux bovins, nous montrons la dépendance d’un paramètre d’atténuation aux propriétés osseuses et à la micro-structure. De plus, ce paramètre semble plus sensible aux propriétés osseuses que ne l’est la vitesse de l’onde longitudinale. Ainsi, l’atténuation évaluée en complément de la vitesse pourrait permettre de caractériser de manière plus complète l’os cortical / This work deals with the ultrasonic characterization of cortical bone. In a first part, the signals acquired with a 1-MHz axial transmission device are analyzed. A later contribution occuring after the first arriving signal is studied after the application of a wave separation procedure. This contribution is shown to be of interest for the ultrasonic characterization of cortical bone. Indeed, experiments performed in vitro on human radii show that this contribution is associated with a flexural wave guided which is dependent on the cortical thickness. In addition, this contribution has a lower frequency content than the first arriving signal and is associated with a different propagation mode. Therefore, a more thorough analysis of the ultrasonic signals enables a multi-modal/multi-frequency approach. In a second part, the ultrasonic attenuation is evaluated in an in vitro experimental study on bovine cortical bone samples. Ultrasonic attenuation is shown to be dependent on bone properties and micro-structure. Furthermore, this parameter seems to be more sensitive than the longitudinal wave velocity to bone parameters. Attenuation, in combination with ultrasonic wave velocity, is of interest and may provide a more comprehensive characterization of cortical bone

No description available.

The need to quantify distance between two groups of objects is prevalent throughout the signal processing world. The difference of group means computed using the Euclidean, or L2 distance, is one of the predominant distance measures used to compare feature vectors and groups of vectors, but many problems arise with it when high data dimensionality is present. Maximum mean discrepancy (MMD) is a recent unsupervised kernel-based pattern recognition method which may improve differentiation between two distinct populations over many commonly used methods such as the difference of means, when paired with the proper feature representations and kernels. MMD-based distance computation combines many powerful concepts from the machine learning literature, such as data distribution-leveraging similarity measures and kernel methods for machine learning. Due to this heritage, we posit that dissimilarity-based classification and changepoint detection using MMD can lead to enhanced separation between different populations. To test this hypothesis, we conduct studies comparing MMD and the difference of means in two subareas of image analysis and understanding: first, to detect scene changes in video in an unsupervised manner, and secondly, in the biomedical imaging field, using clinical ultrasound to assess tumor response to treatment. We leverage effective computer vision data descriptors, such as the bag-of-visual-words and sparse combinations of SIFT descriptors, and choose from an assessment of several similarity kernels (e.g. Histogram Intersection, Radial Basis Function) in order to engineer useful systems using MMD. Promising improvements over the difference of means, measured primarily using precision/recall for scene change detection, and k-nearest neighbour classification accuracy for tumor response assessment, are obtained in both applications.