Libertario Demi | IMEC - Academia.edu (original) (raw)
Papers by Libertario Demi
2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2014
This work provides a feasibility study on estimating the 3-D locations of several thousand miniat... more This work provides a feasibility study on estimating the 3-D locations of several thousand miniaturized freefloating sensor platforms. The localization is performed on basis of sparse ultrasound range measurements between sensor platforms and without the use of beacons.
Objectives The aim of this study is to improve the accuracy of dynamic contrast-enhanced ultrasou... more Objectives The aim of this study is to improve the accuracy of dynamic contrast-enhanced ultrasound (DCE-US) for prostate cancer (PCa) localization by means of a multiparametric approach. Materials and Methods Thirteen different parameters related to either perfusion or dispersion were extracted pixel-by-pixel from 45 DCE-US recordings in 19 patients referred for radical prostatectomy. Multiparametric maps were retrospectively produced using a Gaussian mixture model algorithm. These were subsequently evaluated on their pixel-wise performance in classifying 43 benign and 42 malignant histopathologically confirmed regions of interest, using a prostate-based leave-one-out procedure. Results The combination of the spatiotemporal correlation (r), mean transit time (μ), curve skewness (κ), and peak time (PT) yielded an accuracy of 81% ± 11%, which was higher than the best performing single parameters: r (73%), μ (72%), and washin time (72%). The negative predictive value increased to 83% ± 16% from 70%, 69% and 67%, respectively. Pixel inclusion based on the confidence level boosted these measures to 90% with half of the pixels excluded, but without disregarding any prostate or region. Conclusions Our results suggest multiparametric DCE-US analysis might be a useful diagnostic tool for PCa, possibly supporting future targeting of biopsies or therapy. Application in other types of cancer can also be foreseen. Key points • DCE-US can be used to extract both perfusion and dispersion-related parameters. • Multiparametric DCE-US performs better in detecting PCa than single-parametric DCE-US. • Multiparametric DCE-US might become a useful tool for PCa localization. Abbreviations AT Appearance time CUDI Contrast-ultrasound dispersion imaging DCE-US Dynamic contrast-enhanced ultrasound FWHM Full width half mximum GMM Gaussian mixture model LDRW Local density random walk mpMRI Multiparametric magnetic resonance imaging NPV Negative predictive value PCa Prostate cancer PPV Positive predictive value PSA Prostate-specific antigen PT Peak time ROC Receiver operating characteristic ROI Region of interest TIC Time-intensity curve TRUS Transrectal ultrasound UCA Ultrasound contrast agent WIT Wash-in time * Rogier R. Wildeboer
We report on the first study demonstrating the ability of a recently-developed, contrast-enhanced... more We report on the first study demonstrating the ability of a recently-developed, contrast-enhanced, ultrasound imaging method, referred to as cumulative phase delay imaging (CPDI), to image and quantify ultrasound contrast agent (UCA) kinetics. Unlike standard ultrasound tomography, which exploits changes in speed of sound and attenuation, CPDI is based on a marker specific to UCAs, thus enabling dynamic contrast-specific ultrasound tomography (DCS-UST). For breast imaging, DCS-UST will lead to a more practical, faster, and less operator-dependent imaging procedure compared to standard echo-contrast, while preserving accurate imaging of contrast kinetics. Moreover, a linear relation between CPD values and ultrasound second-harmonic intensity was measured (coefficient of determination = 0.87). DCS-UST can find clinical applications as a diagnostic method for breast cancer localization, adding important features to multi-parametric ultrasound tomography of the breast. Nowadays, there is growing interest in the development of imaging techniques which are capable of detecting and localizing angiogenesis and neovascularization. These processes induce specific changes in the microvas-cular structure, represent an established marker for tumours, and also provide indications of tumour aggressiveness 1. In particular, dynamic contrast-enhanced ultrasound (DCE-US) imaging shows promise, with many novel approaches focusing on the direct and/or indirect characterization of the microvasculature. However, when considering the various imaging options, several challenges emerge for imaging the breast. Typical ultrasound contrast agents (UCAs) are gas-filled microbubbles with diameters ranging between 1 and 10 μ m; they are therefore suitable for intravenous injection and can flow through the smallest microvessels. This phenomenon is exploited by super-localization ultrasound techniques which overcome the diffraction limit and are capable of imaging the microvasculature with a spatial-resolution as small as 8–12 μ m 2,3. Additionally, these techniques provide access to accurate velocity maps, thus offering a powerful tool for the study of microvascu-lar blood flow. However, the relatively long imaging time needed (e.g., > 2 minutes per plane 2), the influence of motion, and the difficulties in imaging and localizing single microbubbles in deep tissue, pose limitations to the use of these modalities in large organs. Another recently-developed imaging method is acoustic angiography 4. With this technique, high spatial-resolution images (in the order of 100 μ m) are obtained using tenfold higher frequencies than with normal DCE-US echo-imaging. Once again, the key lies in the UCAs peculiar response to ultrasound. Because of their highly nonlinear behaviour, UCAs can backscatter high-frequency broadband echo signals (15–35 MHz), which can be used to achieve improved spatial-resolution 5. However, frequency-dependent attenuation practically constrains the applicability of this technique to relatively small depths, such as those required for imaging the peripheral zone of the prostate (1–2 cm). Other techniques chose a different path rather than targeting high spatial-resolution. Standard DCE-US imaging (i.e., Harmonic Imaging, Pulse Inversion, and Amplitude Modulation) is an echo graphic technique, which in essence exploits variations in the second harmonic amplitude to generate real-time images of UCA kinetics when flowing through the vasculature 6,7. In particular, the analysis of microbubble flow-dynamics through the vessels can be used to reveal changes in the vasculature itself. To this end, several techniques which are based on the quantification of parameters related to UCA perfusion and dispersion have been proposed 8–12. Although the typical DCE-US spatial resolution is in the order of 1 mm, hence unsuitable for imaging microvascular changes, these techniques are still able to infer relevant information in relation to the 'angiogenetic switch' (the transition from a pre-vascular to a vascularized tumour phenotype) required for cancer to grow beyond 1–2 mm in diameter 13,14 .
Physics in medicine and biology, Jan 7, 2015
Standard dynamic-contrast enhanced ultrasound (DCE-US) imaging detects and estimates ultrasound-c... more Standard dynamic-contrast enhanced ultrasound (DCE-US) imaging detects and estimates ultrasound-contrast-agent (UCA) concentration based on the amplitude of the nonlinear (harmonic) components generated during ultrasound (US) propagation through UCAs. However, harmonic components generation is not specific to UCAs, as it also occurs for US propagating through tissue. Moreover, nonlinear artifacts affect standard DCE-US imaging, causing contrast to tissue ratio reduction, and resulting in possible misclassification of tissue and misinterpretation of UCA concentration. Furthermore, no contrast-specific modality exists for DCE-US tomography; in particular speed-of-sound changes due to UCAs are well within those caused by different tissue types. Recently, a new marker for UCAs has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental component is in fact observable for US propagating through UCAs, and is absent in tissue. In this paper, tomographic ...
Diagnostic medical ultrasound employs acoustic wave fields to image internal parts of the human b... more Diagnostic medical ultrasound employs acoustic wave fields to image internal parts of the human body. For low amplitude acoustic wave fields, the speed of sound may be considered to be only medium dependent, whereas for high amplitude fields, it becomes also pressure dependent. As a result, the wave travels faster during the high pressure phase than during the lower pressure phase, leading to a deformation of the wave form. This phenomenon is a manifestation of nonlinear acoustics and plays a key role in the development of new medical diagnostic modalities. Obtaining in-depth understanding of the nonlinear phenomena and making optimal use of nonlinear acoustics in new scanning system requires a computer model that can accurately simulate the nonlinear propagation of the acoustic wave field in biomedical tissue. To meet the demand for a computer model, in the previous years we have developed the Iterative Nonlinear Contrast Source (INCS) method, which is a directionally independent 4...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Imaging the acoustical coefficient of nonlinearity, β, is of interest in several healthcare inter... more Imaging the acoustical coefficient of nonlinearity, β, is of interest in several healthcare interventional applications. It is an important feature that can be used for discriminating tissues. In this paper, we propose a nonlinearity characterization method with the goal of locally estimating the coefficient of nonlinearity. The proposed method is based on a 1-D solution of the nonlinear lossy Westerfelt equation, thereby deriving a local relation between β and the pressure wave field. Based on several assumptions, a β imaging method is then presented that is based on the ratio between the harmonic and fundamental fields, thereby reducing the effect of spatial amplitude variations of the speckle pattern. By testing the method on simulated ultrasound pressure fields and an in vitro B-mode ultrasound acquisition, we show that the designed algorithm is able to estimate the coefficient of nonlinearity, and that the tissue types of interest are well discriminable. The proposed imaging me...
2014 IEEE International Ultrasonics Symposium, 2014
Nonlinear propagation is important in many diagnostic and therapeutic applications of medical ult... more Nonlinear propagation is important in many diagnostic and therapeutic applications of medical ultrasound. The design of equipment and protocols for nonlinear modalities is facilitated by the simulation of the nonlinear ultrasound field. However, many existing simulation tools have difficulties of dealing with realistic features like tissue inhomogeneity, power law losses, or steered beams. Recently, two full-wave simulation methods for nonlinear ultrasound have been developed that are able to deal with these features. Those methods are known as the Iterative Nonlinear Contrast Source method (INCS; an integral equation method) and k-Wave (a pseudospectral time domain method). This paper assesses the accuracy of both methods by comparing their spatial and spectral results for two test configurations. In both configurations, a square piston excites a three-cycle Gaussian-modulated tone burst with a center frequency of 1 MHz and a source pressure of 750 kPa. The medium in the first configuration is homogeneous and has a speed of sound, density of mass and parameter of nonlinearity equal to that of water, and a power law attenuation with an exponent 1.5 and a magnitude of 0.75 dB/cm at 1 MHz. In the second configuration, the medium has been made inhomogeneous by putting a hollow cylinder (speed of sound equal to 1540 m/s) and a solid sphere (parameter of nonlinearity equal to 1) in the course of the radiated beam. In both cases, the results obtained with INCS and k-Wave are in excellent agreement, with maximum local differences in the order of 0.5-0.6 dB in the significant parts of the field. Because both methods are computationally quite different, it is improbable that these both suffer from the same systematic error. Hence it is established that both methods are correct and highly accurate, and are suitable tools for performing precise simulations and generating accuracy benchmarks.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Currently, nonradical treatment for prostate cancer is hampered by the lack of reliable diagnosti... more Currently, nonradical treatment for prostate cancer is hampered by the lack of reliable diagnostics. Contrastultrasound dispersion imaging (CUDI) has recently shown great potential as a prostate cancer imaging technique. CUDI estimates the local dispersion of intravenously injected contrast agents, imaged by transrectal dynamic contrast-enhanced ultrasound (DCE-US), to detect angiogenic processes related to tumor growth. The best CUDI results have so far been obtained by similarity analysis of the contrast kinetics in neighboring pixels. To date, CUDI has been investigated in 2-D only. In this paper, an implementation of 3-D CUDI based on spatiotemporal similarity analysis of 4-D DCE-US is described. Different from 2-D methods, 3-D CUDI permits analysis of the entire prostate using a single injection of contrast agent. To perform 3-D CUDI, a new strategy was designed to estimate the similarity in the contrast kinetics at each voxel, and data processing steps were adjusted to the cha...
2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2014
This work provides a feasibility study on estimating the 3-D locations of several thousand miniat... more This work provides a feasibility study on estimating the 3-D locations of several thousand miniaturized freefloating sensor platforms. The localization is performed on basis of sparse ultrasound range measurements between sensor platforms and without the use of beacons.
IEEE transactions on bio-medical engineering, Jan 10, 2015
Ultrasound Computed Tomography (UCT) allows reconstruction of quantitative tissue characteristics... more Ultrasound Computed Tomography (UCT) allows reconstruction of quantitative tissue characteristics such as speed of sound, mass density and attenuation. Lowering its acquisition time would be beneficial; however, this is fundamentally limited by the physical time of flight and the number of transmission events. In this paper, we propose a Compressed Sensing solution for UCT. The adopted measurement scheme is based on compressed acquisitions, with concurrent randomized transmissions in a circular array configuration. Reconstruction of the image is then obtained by combining the Born Iterative Method and Total Variation minimization, thereby exploiting variation sparsity in the image domain. Evaluation using simulated UCT scattering measurements shows that the proposed transmission scheme performs better than uniform undersampling and is able to reduce acquisition time by almost one order of magnitude, while maintaining high spatial resolution.
The Journal of the Acoustical Society of America, 2014
Several imaging techniques aimed at detecting ultrasound contrast agents (UCAs) echo signals, whi... more Several imaging techniques aimed at detecting ultrasound contrast agents (UCAs) echo signals, while suppressing signals coming from the surrounding tissue, have been developed. These techniques are especially relevant for blood flow, perfusion, or contrast dispersion quantification. However, despite several approaches being presented, improving the understanding of the ultrasound/UCAs interaction may support further development of imaging techniques. In this paper, the physical phenomena behind the formation of harmonic components in tissue and UCAs, respectively, are addressed as a possible way to recognize the origin of the echo signals. Simulations based on a modified Rayleigh, Plesset, Noltingk, Neppiras, and Poritsky equation and transmission and backscattering measurements of ultrasound propagating through UCAs performed with a single element transducer and a submergible hydrophone, are presented. Both numerical and in vitro results show the occurrence of a cumulative time delay between the second harmonic and fundamental component which increases with UCA concentration and propagation path length through UCAs, and that was clearly observable at frequencies (f 0 ¼ 2.5 MHz) and pressure regimes (mechanical index ¼ 0.1) of interest for imaging. Most importantly, this delay is not observed in the absence of UCAs. In conclusion, the reported phenomenon represents a marker for UCAs with potential application for imaging.
2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2014
This work provides a feasibility study on estimating the 3-D locations of several thousand miniat... more This work provides a feasibility study on estimating the 3-D locations of several thousand miniaturized freefloating sensor platforms. The localization is performed on basis of sparse ultrasound range measurements between sensor platforms and without the use of beacons.
Objectives The aim of this study is to improve the accuracy of dynamic contrast-enhanced ultrasou... more Objectives The aim of this study is to improve the accuracy of dynamic contrast-enhanced ultrasound (DCE-US) for prostate cancer (PCa) localization by means of a multiparametric approach. Materials and Methods Thirteen different parameters related to either perfusion or dispersion were extracted pixel-by-pixel from 45 DCE-US recordings in 19 patients referred for radical prostatectomy. Multiparametric maps were retrospectively produced using a Gaussian mixture model algorithm. These were subsequently evaluated on their pixel-wise performance in classifying 43 benign and 42 malignant histopathologically confirmed regions of interest, using a prostate-based leave-one-out procedure. Results The combination of the spatiotemporal correlation (r), mean transit time (μ), curve skewness (κ), and peak time (PT) yielded an accuracy of 81% ± 11%, which was higher than the best performing single parameters: r (73%), μ (72%), and washin time (72%). The negative predictive value increased to 83% ± 16% from 70%, 69% and 67%, respectively. Pixel inclusion based on the confidence level boosted these measures to 90% with half of the pixels excluded, but without disregarding any prostate or region. Conclusions Our results suggest multiparametric DCE-US analysis might be a useful diagnostic tool for PCa, possibly supporting future targeting of biopsies or therapy. Application in other types of cancer can also be foreseen. Key points • DCE-US can be used to extract both perfusion and dispersion-related parameters. • Multiparametric DCE-US performs better in detecting PCa than single-parametric DCE-US. • Multiparametric DCE-US might become a useful tool for PCa localization. Abbreviations AT Appearance time CUDI Contrast-ultrasound dispersion imaging DCE-US Dynamic contrast-enhanced ultrasound FWHM Full width half mximum GMM Gaussian mixture model LDRW Local density random walk mpMRI Multiparametric magnetic resonance imaging NPV Negative predictive value PCa Prostate cancer PPV Positive predictive value PSA Prostate-specific antigen PT Peak time ROC Receiver operating characteristic ROI Region of interest TIC Time-intensity curve TRUS Transrectal ultrasound UCA Ultrasound contrast agent WIT Wash-in time * Rogier R. Wildeboer
We report on the first study demonstrating the ability of a recently-developed, contrast-enhanced... more We report on the first study demonstrating the ability of a recently-developed, contrast-enhanced, ultrasound imaging method, referred to as cumulative phase delay imaging (CPDI), to image and quantify ultrasound contrast agent (UCA) kinetics. Unlike standard ultrasound tomography, which exploits changes in speed of sound and attenuation, CPDI is based on a marker specific to UCAs, thus enabling dynamic contrast-specific ultrasound tomography (DCS-UST). For breast imaging, DCS-UST will lead to a more practical, faster, and less operator-dependent imaging procedure compared to standard echo-contrast, while preserving accurate imaging of contrast kinetics. Moreover, a linear relation between CPD values and ultrasound second-harmonic intensity was measured (coefficient of determination = 0.87). DCS-UST can find clinical applications as a diagnostic method for breast cancer localization, adding important features to multi-parametric ultrasound tomography of the breast. Nowadays, there is growing interest in the development of imaging techniques which are capable of detecting and localizing angiogenesis and neovascularization. These processes induce specific changes in the microvas-cular structure, represent an established marker for tumours, and also provide indications of tumour aggressiveness 1. In particular, dynamic contrast-enhanced ultrasound (DCE-US) imaging shows promise, with many novel approaches focusing on the direct and/or indirect characterization of the microvasculature. However, when considering the various imaging options, several challenges emerge for imaging the breast. Typical ultrasound contrast agents (UCAs) are gas-filled microbubbles with diameters ranging between 1 and 10 μ m; they are therefore suitable for intravenous injection and can flow through the smallest microvessels. This phenomenon is exploited by super-localization ultrasound techniques which overcome the diffraction limit and are capable of imaging the microvasculature with a spatial-resolution as small as 8–12 μ m 2,3. Additionally, these techniques provide access to accurate velocity maps, thus offering a powerful tool for the study of microvascu-lar blood flow. However, the relatively long imaging time needed (e.g., > 2 minutes per plane 2), the influence of motion, and the difficulties in imaging and localizing single microbubbles in deep tissue, pose limitations to the use of these modalities in large organs. Another recently-developed imaging method is acoustic angiography 4. With this technique, high spatial-resolution images (in the order of 100 μ m) are obtained using tenfold higher frequencies than with normal DCE-US echo-imaging. Once again, the key lies in the UCAs peculiar response to ultrasound. Because of their highly nonlinear behaviour, UCAs can backscatter high-frequency broadband echo signals (15–35 MHz), which can be used to achieve improved spatial-resolution 5. However, frequency-dependent attenuation practically constrains the applicability of this technique to relatively small depths, such as those required for imaging the peripheral zone of the prostate (1–2 cm). Other techniques chose a different path rather than targeting high spatial-resolution. Standard DCE-US imaging (i.e., Harmonic Imaging, Pulse Inversion, and Amplitude Modulation) is an echo graphic technique, which in essence exploits variations in the second harmonic amplitude to generate real-time images of UCA kinetics when flowing through the vasculature 6,7. In particular, the analysis of microbubble flow-dynamics through the vessels can be used to reveal changes in the vasculature itself. To this end, several techniques which are based on the quantification of parameters related to UCA perfusion and dispersion have been proposed 8–12. Although the typical DCE-US spatial resolution is in the order of 1 mm, hence unsuitable for imaging microvascular changes, these techniques are still able to infer relevant information in relation to the 'angiogenetic switch' (the transition from a pre-vascular to a vascularized tumour phenotype) required for cancer to grow beyond 1–2 mm in diameter 13,14 .
Physics in medicine and biology, Jan 7, 2015
Standard dynamic-contrast enhanced ultrasound (DCE-US) imaging detects and estimates ultrasound-c... more Standard dynamic-contrast enhanced ultrasound (DCE-US) imaging detects and estimates ultrasound-contrast-agent (UCA) concentration based on the amplitude of the nonlinear (harmonic) components generated during ultrasound (US) propagation through UCAs. However, harmonic components generation is not specific to UCAs, as it also occurs for US propagating through tissue. Moreover, nonlinear artifacts affect standard DCE-US imaging, causing contrast to tissue ratio reduction, and resulting in possible misclassification of tissue and misinterpretation of UCA concentration. Furthermore, no contrast-specific modality exists for DCE-US tomography; in particular speed-of-sound changes due to UCAs are well within those caused by different tissue types. Recently, a new marker for UCAs has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental component is in fact observable for US propagating through UCAs, and is absent in tissue. In this paper, tomographic ...
Diagnostic medical ultrasound employs acoustic wave fields to image internal parts of the human b... more Diagnostic medical ultrasound employs acoustic wave fields to image internal parts of the human body. For low amplitude acoustic wave fields, the speed of sound may be considered to be only medium dependent, whereas for high amplitude fields, it becomes also pressure dependent. As a result, the wave travels faster during the high pressure phase than during the lower pressure phase, leading to a deformation of the wave form. This phenomenon is a manifestation of nonlinear acoustics and plays a key role in the development of new medical diagnostic modalities. Obtaining in-depth understanding of the nonlinear phenomena and making optimal use of nonlinear acoustics in new scanning system requires a computer model that can accurately simulate the nonlinear propagation of the acoustic wave field in biomedical tissue. To meet the demand for a computer model, in the previous years we have developed the Iterative Nonlinear Contrast Source (INCS) method, which is a directionally independent 4...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Imaging the acoustical coefficient of nonlinearity, β, is of interest in several healthcare inter... more Imaging the acoustical coefficient of nonlinearity, β, is of interest in several healthcare interventional applications. It is an important feature that can be used for discriminating tissues. In this paper, we propose a nonlinearity characterization method with the goal of locally estimating the coefficient of nonlinearity. The proposed method is based on a 1-D solution of the nonlinear lossy Westerfelt equation, thereby deriving a local relation between β and the pressure wave field. Based on several assumptions, a β imaging method is then presented that is based on the ratio between the harmonic and fundamental fields, thereby reducing the effect of spatial amplitude variations of the speckle pattern. By testing the method on simulated ultrasound pressure fields and an in vitro B-mode ultrasound acquisition, we show that the designed algorithm is able to estimate the coefficient of nonlinearity, and that the tissue types of interest are well discriminable. The proposed imaging me...
2014 IEEE International Ultrasonics Symposium, 2014
Nonlinear propagation is important in many diagnostic and therapeutic applications of medical ult... more Nonlinear propagation is important in many diagnostic and therapeutic applications of medical ultrasound. The design of equipment and protocols for nonlinear modalities is facilitated by the simulation of the nonlinear ultrasound field. However, many existing simulation tools have difficulties of dealing with realistic features like tissue inhomogeneity, power law losses, or steered beams. Recently, two full-wave simulation methods for nonlinear ultrasound have been developed that are able to deal with these features. Those methods are known as the Iterative Nonlinear Contrast Source method (INCS; an integral equation method) and k-Wave (a pseudospectral time domain method). This paper assesses the accuracy of both methods by comparing their spatial and spectral results for two test configurations. In both configurations, a square piston excites a three-cycle Gaussian-modulated tone burst with a center frequency of 1 MHz and a source pressure of 750 kPa. The medium in the first configuration is homogeneous and has a speed of sound, density of mass and parameter of nonlinearity equal to that of water, and a power law attenuation with an exponent 1.5 and a magnitude of 0.75 dB/cm at 1 MHz. In the second configuration, the medium has been made inhomogeneous by putting a hollow cylinder (speed of sound equal to 1540 m/s) and a solid sphere (parameter of nonlinearity equal to 1) in the course of the radiated beam. In both cases, the results obtained with INCS and k-Wave are in excellent agreement, with maximum local differences in the order of 0.5-0.6 dB in the significant parts of the field. Because both methods are computationally quite different, it is improbable that these both suffer from the same systematic error. Hence it is established that both methods are correct and highly accurate, and are suitable tools for performing precise simulations and generating accuracy benchmarks.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Currently, nonradical treatment for prostate cancer is hampered by the lack of reliable diagnosti... more Currently, nonradical treatment for prostate cancer is hampered by the lack of reliable diagnostics. Contrastultrasound dispersion imaging (CUDI) has recently shown great potential as a prostate cancer imaging technique. CUDI estimates the local dispersion of intravenously injected contrast agents, imaged by transrectal dynamic contrast-enhanced ultrasound (DCE-US), to detect angiogenic processes related to tumor growth. The best CUDI results have so far been obtained by similarity analysis of the contrast kinetics in neighboring pixels. To date, CUDI has been investigated in 2-D only. In this paper, an implementation of 3-D CUDI based on spatiotemporal similarity analysis of 4-D DCE-US is described. Different from 2-D methods, 3-D CUDI permits analysis of the entire prostate using a single injection of contrast agent. To perform 3-D CUDI, a new strategy was designed to estimate the similarity in the contrast kinetics at each voxel, and data processing steps were adjusted to the cha...
2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2014
This work provides a feasibility study on estimating the 3-D locations of several thousand miniat... more This work provides a feasibility study on estimating the 3-D locations of several thousand miniaturized freefloating sensor platforms. The localization is performed on basis of sparse ultrasound range measurements between sensor platforms and without the use of beacons.
IEEE transactions on bio-medical engineering, Jan 10, 2015
Ultrasound Computed Tomography (UCT) allows reconstruction of quantitative tissue characteristics... more Ultrasound Computed Tomography (UCT) allows reconstruction of quantitative tissue characteristics such as speed of sound, mass density and attenuation. Lowering its acquisition time would be beneficial; however, this is fundamentally limited by the physical time of flight and the number of transmission events. In this paper, we propose a Compressed Sensing solution for UCT. The adopted measurement scheme is based on compressed acquisitions, with concurrent randomized transmissions in a circular array configuration. Reconstruction of the image is then obtained by combining the Born Iterative Method and Total Variation minimization, thereby exploiting variation sparsity in the image domain. Evaluation using simulated UCT scattering measurements shows that the proposed transmission scheme performs better than uniform undersampling and is able to reduce acquisition time by almost one order of magnitude, while maintaining high spatial resolution.
The Journal of the Acoustical Society of America, 2014
Several imaging techniques aimed at detecting ultrasound contrast agents (UCAs) echo signals, whi... more Several imaging techniques aimed at detecting ultrasound contrast agents (UCAs) echo signals, while suppressing signals coming from the surrounding tissue, have been developed. These techniques are especially relevant for blood flow, perfusion, or contrast dispersion quantification. However, despite several approaches being presented, improving the understanding of the ultrasound/UCAs interaction may support further development of imaging techniques. In this paper, the physical phenomena behind the formation of harmonic components in tissue and UCAs, respectively, are addressed as a possible way to recognize the origin of the echo signals. Simulations based on a modified Rayleigh, Plesset, Noltingk, Neppiras, and Poritsky equation and transmission and backscattering measurements of ultrasound propagating through UCAs performed with a single element transducer and a submergible hydrophone, are presented. Both numerical and in vitro results show the occurrence of a cumulative time delay between the second harmonic and fundamental component which increases with UCA concentration and propagation path length through UCAs, and that was clearly observable at frequencies (f 0 ¼ 2.5 MHz) and pressure regimes (mechanical index ¼ 0.1) of interest for imaging. Most importantly, this delay is not observed in the absence of UCAs. In conclusion, the reported phenomenon represents a marker for UCAs with potential application for imaging.