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ABSTRACT: Today's society is exposed to an increasing number of disasters and large scale emergencies (e.g. earthquake in Haiti, global swine flu, or manmade disasters like the oil spill in the Gulf of Mexico). Information and communication technology (ICT) can help to prevent and mitigate the effects of threatening situations if applied appropriately. In industry ICT governance methods have become important tools to successfully align ICT with business goals. However, the domain of emergency management (EM) has to deal with unpredictable situations, multi organizational collaborations and ad-hoc teams, conditions which make conventional ICT governance frameworks and methods less useful. Based on a qualitative analysis of several European and Australian EM organizations and government agencies this paper discusses the issues and benefits of strategic ICT alignment in EM and identifies the current barriers and the special requirements of this domain. Finally, it presents a prototypical approach to fill this gap.
System Sciences (HICSS), 2011 44th Hawaii International Conference on; 02/2011
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ABSTRACT: At last year's conference, we presented a synthetic aperture image reconstruction technique (PSF-SAFT) for fixed-focus single-element ultrasound transducers. It is based on the correlation of the recorded echo signals with the simulated depth-dependent point spread function (PSF) of the ultrasound imaging system. Compared to conventional delay-and-sum (DAS) methods, it results in a higher signal-to-noise-ratio (SNR) but lower axial and lateral resolution. In this contribution the synthetic aperture focusing technique is further developed by inverse filtering of the simulated PSFs and coherence factor (CF) weighting for increased resolution and suppression of side lobes, respectively. The proposed method was evaluated using a 20 MHz ultrasound system with a spherically-focused transducer. With measurements on a wire phantom the transducer's resolution in focus was determined and compared to DAS-SAFT and PSF-SAFT processed datasets, with and without CF-weighting. While the spatial resolution does not differ significantly, PSF-SAFT with CF-weighting results in the highest reduction of noise and side lobes.
Ultrasonics Symposium (IUS), 2010 IEEE; 11/2010
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ABSTRACT: A detailed review is given of the application of high-frequency ultrasound (HFUS) at frequencies of 20 MHz and above for high-resolution, cross-sectional imaging of biological soft tissue. The state of the art of HFUS imaging systems is discussed with respect to the underlying engineering concepts, system designs, and available transducer technology. Furthermore, the dependency of the spatial resolution on the system's parameters is analysed. Skin imaging, eye imaging, small animal imaging for preclinical research, and intravascular ultrasound in coronary arteries for arteriosclerotic disease diagnostics are presented as examples for the application of HFUS imaging in medical diagnostics. It is shown that, in the frame of the indicated applications, ultrasound in the frequency range 20-100MHz gives a good compromise between the contrary demands for a good spatial resolution and a sufficiently large penetration depth of ultrasound waves into the tissue. Scanning schemes for the imaging of tissue morphology are considered, including spatial compounding as a multidirectional imaging technique.
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 01/2010; 224(2):225-40. · 1.21 Impact Factor
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ABSTRACT: In this paper, an approach for the imaging of planar surface structures with high-frequency ultrasound in the 20 MHz frequency range is presented and evaluated. Planar material samples are placed in the far field of a single element transducer, and echo signals are acquired in a monostatic, side looking configuration during one or more scans along the azimuth direction. Synthetic aperture focusing is utilized for the reconstruction of B-mode images, which represent the echogenicity along the two-dimensional planar surface. The concept has been evaluated with a spherically focused transducer under the assumption of a virtual point source and under the approximation that spherical waves emanate from the transducer focus. Results from both, simulated echo data and measurement data from test objects, are presented and discussed.
Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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ABSTRACT: A synthetic aperture focusing approach is presented, which is based on the cross-correlation of the measured data with the simulated depth-dependent response to a point scatterer of the imaging system. The method has been evaluated by measurements using a 20 MHz ultrasound system with a fixed-focus single-element transducer. The simulation of the system's response is carried out with Field II. Measurements of a wire phantom show a depth-independent lateral and axial resolution below the focal point, even for large imaging depths and an increase of signal-to-noise ratio (SNR). These results are confirmed with small animal imaging experiments. The method is applicable to the near- and the far-field of the transducer, given that it is possible to simulate the system response.
Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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ABSTRACT: In high-frequency ultrasound (HFUS) imaging systems usually mechanically moved single-element fixed-focus transducers are used, and a water path between transducer and the object (tissue area) is required. The speed of sound (SoS) differences of water and tissue causes beam refraction at the boundary. When applying spatial compounding by superposition of B-mode images obtained from different angles of insonation, time-of-flight (ToF) and refraction artifacts appear and reduce image resolution and contrast. Both are analyzed based on an analytical model, which assumes different but spatially constant SoS for the water and the tissue regions, respectively. For correction, a ray tracing algorithm is applied to the individual images used for compounding. The SoS of water is obtained experimentally by wire phantom measurements, and the SoS of the tissue, which is not exactly known, is iteratively changed to optimize the compound image in terms of resolution. Due to refraction and ToF errors, imaged structures appear at different positions for different angles of insonation. The position shift of a point-like scatterer is taken as a measure of the image correction quality. By minimizing this shift compared to uncorrected images, the mean SoS of the tissue can be determined. The superposition of image frames after the final correction step delivers the compound image with optimized resolution and image contrast. For evaluation, the scheme has been applied to wire phantom measurements and to measurements on a rat pup cadaver. The corrected compound images show improved image contrast and resolution.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: In this paper, an approach for the extraction of quantitative parameters from multi-directional ultrasound echo signal data for the differentiation and characterization of specular reflections and diffuse backscattering is presented and evaluated. Spatially resolved, tissue-characterizing parametric images are calculated by analyzing the envelope of echo signals from different insonation angles. Frames of echo signals, which are acquired with a limited-angle spatial compound imaging system, are scan-converted, and the envelope of echo signals at each pixel in the axial / lateral imaging plane is analyzed as a function of the insonation angle. Statistical first-order parameters are directly calculated from this data, and further parameters are derived from fitted model functions. The proposed concept has been evaluated by means of phantom measurements and in vivo measurements on skin with a 20 MHz high-frequency ultrasound (HFUS) system for limited-angle (up to +/-40deg) pulse-echo measurements. Results of measurements on a plastic tube, which is surrounded by a speckle phantom, show that specular reflections can be distinguished from diffuse backscattering. Furthermore, the surface orientation of specular reflectors is depicted in parametric images. In vivo images of skin show that specular reflections, for example at scar tissue and at the border between the dermis and the subcutaneous fat, can be detected and differentiated from their surrounding based on the proposed parameters.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: For ultrasound imaging of small animals often standard systems for human medicine or special high frequency ultrasound systems are used. The former are limited to frequencies below 15 MHz, and therefore their spatial resolution often is not sufficient. High-frequency ultrasound (HFUS) imaging systems working at frequencies up to 40 MHz offer a rather high resolution, but high ultrasound frequencies and mainly used fixed-focus transducers lead to a limited depth of field (DOF). In this paper, a 20 MHz HFUS imaging system operating in a limited angle spatial compounding (LASC) mode is applied. It representing a good compromise between depth of field and spatial resolution with an improved image quality due to the LASC operation mode. By stepwise moving the transducer along the elevational direction, three-dimensional (3D) echo datasets are recorded. The system was characterized in terms of axial, lateral, and elevational resolution by means of wire phantom measurments. For further evaluation, measurements on fresh cadavers of 1-day-old rat pups were carried out. Spatial compound images show reduced speckle, a more complete and detailed depiction of tissue structures and less shadowing artifacts compared to conventional B-mode images. The increase of signal-to-noise ratio is analyzed by speckle statistics. Cross sectional images of 3D datasets as well as maximum intensity projections (MIP) and mean intensity projections (MeanIP) are presented.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: Ultrasound spatial compounding has been proven to successfully improve the image contrast, to achieve a more isotropic resolution and to reduce imaging artifacts in comparison with conventional B-mode imaging. For high- frequency ultrasound (HFUS) imaging of skin, usually linear scans only are performed perpendicularly to the axial direction of sound propagation. In this paper the potential of HFUS limited- angle spatial compounding for skin imaging is evaluated. We have implemented a new 20 MHz ultrasound system for limited- angle (up to plusmn40deg) spatial compound imaging. A sophisticated scanner was designed for high-resolution imaging with a spherically focused single-element transducer. The influence of unknown parameters of the system is eliminated by calibration measurements on a wire phantom. The imaging properties of the implemented system were assessed by means of phantom and in vivo measurements. A ray-tracing method for the compensation of artifacts, which are caused by refraction at the skin surface, is proposed and evaluated.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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ABSTRACT: In this paper, a new high frequency ultrasound (HFUS) system for high-resolution skin imaging is presented. For imaging, mechanical
scans are performed with spherically focused single element transducers. Two separate applicators with different transducers
are utilized to fulfill the different requirements for imaging the skin with 20MHz ultrasound and for lower range high resolution
imaging of the uppermost skin layers with HFUS in the 100MHz range. Clinical images were acquired in the imaging lab of the
Dermatological University Hospital. Imaging results of wound healing process and skin lesion nevus investigations are presented
12/2006: pages 137-144;
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Ultrasonics Symposium, 2005 IEEE; 10/2005
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ABSTRACT: High frequency ultrasound (HFUS) in the range above 20 MHz is utilized for high resolution skin and eye imaging. With increasing frequencies, the attenuation of water, which is used as propagation medium between mechanically scanned single element transducers and tissue, becomes increasingly significant. The low pass characteristics of water result in a reduction of the system's center frequency and bandwidth, and thus in a loss of spatial resolution. In this paper, spectral characteristics and spatial resolution of HFUS imaging systems are analyzed. taking the frequency dependent attenuation of water into account. Analytical predictions are compared with measurement results. Spectral analyses, performed on phantoms as well as B-mode images of phantom and in vivo measurements, are presented.
Ultrasonics Symposium, 2004 IEEE; 09/2004
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ABSTRACT: Deep venous thrombosis (DVT) is the formation of a blood clot in one of the deep veins of the body, usually in the leg. Common treatment methods include medication with anticoagulants or surgical thrombectomy. Since treatment of DVT succeeds only during the first 7-10 days, exact age determination of DVT is of high importance for an appropriate treatment decision. However, the accuracy of available methods including sonography, phlebography, CT and MRT is often not sufficient. It has been reported that about 30% of all DVT are wrongly staged using common diagnostic modalities and therefore lead to inadequate therapeutic efforts. Therefore alternative and more accurate approaches for staging DVT are desired. Blood clots leading to venous thrombosis undergo an organization process with increasing age. It is known that changes in mechanical stiffness, acoustical properties and appearance in B-mode images accompany the organization process. Therefore several alternative diagnostic approaches, including elastography and ultrasonic tissue characterization, have been proposed in the past. In this work, 22 thrombi of defined age were induced in pigs. Ultrasonic measurements were carried out after surgical resection of the thrombosed vessel segments. Spectral and texture parameters as well as strain estimates obtained using elastography were used to classify thrombosed vessel segments in vitro and thus distinguish between thrombi of age ≤ 6 days and age > 6 days. A combination of the best performing parameters was processed by a classification system. Total crossvalidation over specimens was done using Euclidian, Mahalanobis, and maximum-likelihood classifiers. 90% of specimens could be classified correctly using maximum-likelihood classifiers.
Ultrasonics Symposium, 2004 IEEE; 09/2004
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ABSTRACT: High frequency ultrasound (HFUS) and intravascular ultrasound (IVUS) based elastography can be utilized for tissue elasticity imaging at a microscopic level. Mechanical strain fields inside the tissue are calculated as the spatial derivatives of estimated displacement fields. A technique for the estimation of 2D displacement fields is presented. Axial and lateral displacements in the imaging plane are estimated by tracking speckle in B-mode images and analyzing phase differences between image spectra. Concept and limitations of the proposed approach are discussed. Results are compared with an approach for 1D axial displacement estimation, which is based on the analysis of radio frequency (RF) echo signals. The implemented techniques were applied to asses skin elasticity and to analyze non-uniform rotational distortions (NURD) in IVUS with rotating single element transducers. Results of in vivo measurements are presented. It is shown that B-mode based strain imaging is feasible, provided that applied strains are sufficiently small to prevent decorrelation of echo signals.
Ultrasonics Symposium, 2004 IEEE; 09/2004
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ABSTRACT: High frequency ultrasound (HFUS) can advantageously be applied for high resolution imaging of tissues over a limited penetration depth in applications like skin and eye imaging. Broadband and sensitive electronics is essential for a good resolution in these system, whereby HFUS specific problems have to be taken into account to preserve bandwidth and resolution. In this paper the design, the development and the optimization of a HFUS system for applications in dermatology are presented. In our setup, a nonlinear expander/limiter network is used to protect the receiver against the large pulsed transmit signal and to keep noise signals off. Furthermore, the transducer is connected through a cable, whose length is not negligible compared to the wavelengths at the applied frequencies. Large and small signal reflectances and transmittances were independently measured based on a time domain reflectometry (TDR) concept and network analysis (NWA), which allowed a subsequent optimization of the imaging properties. A dedicated calibration technique was developed and time/frequency domain equivalency was exploited for the measurements. Results of measurements on technical objects (wires, glass plate) for the assessment of the imaging properties as well as in vivo skin images are presented.
Ultrasonics, 2003 IEEE Symposium on; 11/2003
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ABSTRACT: Noninvasive imaging and characterization of the skin is of great interest in dermatology. In order to get relevant diagnostic information, high-resolution imaging techniques have to be applied. Ultrasonic imaging is a potential method for this purpose where the special requirements concerning the spatial resolution make it essential to apply high frequency ultrasound (HFUS). Alternatively, magnetic resonance imaging (MRI), being a very promising imaging modality, also shows the perspective of becoming a valuable diagnostic tool in dermatology. However, to account for the small dimensions of the structures under observation, very specialized system designs have to be developed. In this paper, a HFUS imaging system working in the 50 MHz and 100 MHz range is applied for high-resolution skin imaging. Furthermore, a commercial MRI-system was equipped with specially designed low noise rf (radio frequency) coils with minimized volume, and customized imaging sequences were applied to optimize the signal-to-noise ratio. With HFUS and high-resolution magnetic resonance (HR-MR) imaging complementary imaging techniques for in vivo biomicroscopy of the skin are available.
Biomedizinische Technik 06/2003; 48(5):130-4. · 0.86 Impact Factor
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ABSTRACT: High frequency ultrasound (HFUS) and optical coherence tomography (OCT) are techniques for high resolution imaging of tissues. The penetration depth of these modalities is limited, but it is sufficiently large enough for non invasive skin imaging. HFUS and OCT are based on the same concept. Waves (ultrasonic waves, respectively light waves) propagate along a narrow beam, are backscattered at tissue inhomogeneities and analyzed over time of flight to obtain spatially resolved morphological information. The objective of this paper is to compare HFUS and OCT in terms of resolution, dynamic range and contrast and to assess their value as tools for high resolution skin imaging. Measurements on phantoms and in vivo have been performed with a 100 MHz ultrasound system and an OCT-scanner working in the near infrared spectrum at 1300 nm wave-length. From the measurements, it can be concluded that OCT delivers an almost isotropic resolution (axial resolution about 5.8 microns, lateral resolution about 4.1 microns), whereas the resolution of the investigated HFUS system is more anisotropic (axial resolution about 9.3 microns, lateral resolution about 60 microns). HFUS and OCT show different penetration depths and a different contrast. Both techniques can, therefore, be combined advantageously in a multimodality approach to account for their individual characteristics.
Biomedizinische Technik 06/2003; 48(5):116-21. · 0.86 Impact Factor
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ABSTRACT: The assessment of skin elasticity as a method to investigate effects of skin ageing, sun exposure and pathological conditions is of greatest interest in dermatology. In this paper a new technique for the evaluation and imaging of skin elasticity in vivo applying ultrasound in the 20 MHz range is presented. In our approach we acquire rf echo signal frames under stepwise increasing negative pressure applied to the skin surface that causes suction. A computer controlled vacuum system with a digital pressure control loop is used for precise and reproducible results. The resulting deformation of the skin surface is analyzed by threshold based segmentation with a nonlinear approach for hair echo signal removal. Local axial strains in the epidermis and dermis are calculated from consecutive rf echo signal frames applying the 'phase root seeking' algorithm. We use the correlation coefficient of windowed and time shift compensated echo signals as a measure for the reliability of the estimated strains. Elastic properties of the subcutaneous fat are assessed analyzing tissue structure movements in B-mode frames. Results from phantom and in vivo measurements are presented. It is shown that strains in the epidermis, dermis and the subcutaneous fat are significantly different. Our results show that 20 MHz ultrasound based strain imaging is a potential tool for skin structures elasticity evaluation.
Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE; 11/2002
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ABSTRACT: In this paper an approach for the combined estimation of axial and transversal velocity with special emphasis on high resolution
is presented. Our proposed approach was tested using simulated data and measurements obtained from a flow phantom. With the
estimated flow profile for the axial velocity it was shown that the flow profile inside the vessel with a diameter of 500
μm and with a flow rate of 0.18 μ1/s was parabolic. The proposed method gives adequate results at the center of the vessel,
while the low velocities at the border are over estimated. With the combined estimation strategy complex vessel structures
with unknown flow directions are taken into consideration. Subject of our future work is the imaging of the microcirculatory
system of the skin.
12/2001: pages 317-324;
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ABSTRACT: Approaches for axial blood velocity estimation with pulsed wave
Doppler (PWD) systems can be separated into time domain, frequency
domain and combined time and frequency domain techniques. The imaging
properties (spatial and velocity resolution) with these approaches are
different and depend on the resolution cell size (determined by
bandwidth and lateral resolution), measurement time (number of A-lines
included into velocity estimation) and flow geometry (insonification
angle, vessel diameter relative to resolution cell size, flow velocity
profile). Simulations have been performed to analyze the imaging
properties under different parameter settings and to find optimal
settings for blood flow imaging in small vessels, where the flow
velocity profile changes significantly over the resolution cell. The
findings were validated with flow phantom measurements and in vivo
measurements on small blood vessels at the back of a human hand using a
high frequency (30-70 MHz) PWD-system
Ultrasonics Symposium, 2000 IEEE; 11/2000
