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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Der Radiologe 38 (1998), S. 492-501 
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Osteosarkom ; MR-Bildgebung ; Röntgen ; Key words Osteosarcoma ; MR imaging ; X-ray
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Osteosarcoma is the most common primary malignant bone tumour with the exception of myeloma. The majority of osteosarcoma cases arise within bone and are called conventional osteosarcoma. Intraosseous variants include telangiectatic, small-cell, low-grade intraosseous and cortical osteosarcoma. Less than 10% of osteosarcomas arise on the surface of bone and are subdivided into periosteal, high-grade surface and parosteal varieties. The imaging features of these subtypes of osteosarcoma are described and the impact on diagnosis highlighted. Using material from over 750 osteosarcomas treated at the author’s centre, this article reviews the role of imaging in the management of this condition. Detection still relies principally on the conventional radiograph with bone scintigraphy and MR imaging useful in occult tumours. Establishing the radiological diagnosis depends on careful analysis of the radiographs, with particular attention paid to the nature and extent of bone destruction, periosteal new bone formation and matrix mineralization. The prudent radiologist will be wary of those bone conditions, such as stress fractures and osteomyelitis, which are frequently mistaken for osteosarcoma. Appropriate surgical staging requires MR imaging of the primary tumour to show the bony and soft tissue extent of the lesion and to confirm/exclude skip metastases and local lymph-node involvement. Staging should also include bone scintigraphy to confirm/exclude multiple lesions and chest CT to confirm/exclude pulmonary metastases. Following definitive surgery, imaging is used in the follow-up to monitor potential local recurrence and the development of pulmonary or osseous metastases.
    Notes: Zusammenfassung Das Osteosarkom ist abgesehen vom Myelom der häufigste primäre bösartige Knochentumor. Die überwiegende Mehrzahl der Osteosarkome kommen innerhalb des Knochens vor und werden „konventionelle Osteosarkome” genannt. Die im Knochen vorkommenden Varianten beinhalten teleangiektatische, kleinzellige, niedrig differenzierte intraossäre und kortikale Osteosarkome. Weniger als 10% der Osteosarkome treten an der Knochenoberfläche auf. Diese werden in periosteale, hochgradig differenzierte, oberflächliche und paraostale Varianten unterteilt. Im folgenden werden Osteosarkom-Bildgebungsmethodik und ihr Einfluß auf Diagnose und Therapie diskutiert. Basis dafür sind 750 Osteosarkomen, die am klinischen Zentrum des Autors behandelt wurden. Die Erkennung des Tumors beruht immer noch auf konventionellen Röntgenaufnahmen, während Knochenszintigraphie und Kernspintomographie helfen, diskrete Tumoren aufzuspüren. Die radiologische Diagnose gründet sich auf sorgfältigen Röntgenbildanalysen, unter spezieller Berücksichtigung von Natur und Ausdehnung der Knochendestruktionen, periostalen Knochenneubildungen und Matrixverkalkungen. Streßfrakturen und Osteomyelitiden können differentialdiagnostische Probleme aufwerfen. Die chirurgische Stadieneinteilung beruht auf der kernspintomographischen Darstellung des Primärtumors. Mit ihrer Hilfe kann das Ausmaß des Tumors in Knochen und Weichteilen erkannt, Metastasen bestätigt oder ausgeschlossen sowie der Befall regionärer Lymphknoten abgegrenzt werden. In die Stadieneinteilung sollte auch Knochenszintigraphie sowie Thoraxcomputertomographie mit einbezogen werden, um multiple Läsionen bzw. Lungenmetastasen auszuschließen. Anschließend an die chirurgische Behandlung wird die Bildgebung in Nachsorgeuntersuchungen eingesetzt, um Lokalrezidive und Lungen- bzw. Knochenmetastasen zu erfassen.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Skeletal radiology 29 (2000), S. 713-716 
    ISSN: 1432-2161
    Keywords: Keywords Synovial sarcoma ; Popliteal cyst ; MR imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Synovial sarcoma is a relatively common soft tissue sarcoma particularly in the adolescent and young adult. We report an unusual case of a synovial sarcoma arising within a popliteal cyst in a 13-year-old female presenting with bilateral popliteal cysts. MR imaging demonstrated the cyst with evidence of subacute haemorrhage and a discrete nodule of tumour.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 477-493 
    ISSN: 0271-2091
    Keywords: Bed friction ; Hydrodynamics ; Shallow sea ; Galerkin ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The mathematical formulation of a three-dimensional shallow sea model using a modal expansion in the veitical is briefly described.The importance of the time discretization of the vertical diffusion term and bottom friction term is discussed in some detail. Both stability theory and numerical calculations show the importance of time centring or evaluating the modal form of the viscosity term at the higher time step in order to develop a numerically efficient algorithm. Similar analysis and calculations show that in shallow water it is essential to time centre or evaluate bottom friction at the higher time step. In the case of linear bottom friction it is shown that this condition can be readily accomplished. However, using a quadratic friction formulation (a more physically realistic form), this cannot be readily achieved. A new algorithm is presented whereby a stable solution can be obtained even in shallow water using quadratic bottom friction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 18 (1994), S. 163-188 
    ISSN: 0271-2091
    Keywords: Non-linear interaction ; Hydrodynamic ; Spectral ; Finite difference ; Tidal current ; Wind-driven current ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A single-point model in the vertical is used to examine the coupling between tidal currents and wind-driven flows in shallow near-coastal regions. Calculations using both a linear slip and a no-slip condition at the sea bed clearly show that coupling between tidal and wind-driven currents cannot occur in a linear model with a time-independent eddy viscosity. However with a physically more realistic time-varying viscosity related to the flow field, coupling does occur, the magnitude of this non-linear interaction depending upon the change in eddy viscosity over a tidal cycle and the intensity of shear in the vertical. A point model in the vertical with flow induced by an oscillatory pressure gradient and an additional constant wind stress is used to examine the influence of viscosity parametrization and water depth upon this coupling.The solution in the vertical is accomplished using both a functional approach and a finite difference method. Some conclusions as to the relative merits of these approaches, particularly the use of a transformed grid in the case of high-shear surface and bed boundary layers, are made in the paper.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 33-60 
    ISSN: 0271-2091
    Keywords: Vertical ; Eddy ; Viscosity ; Galerkin ; Method ; Hydrodynamic ; Model ; Eigenfunction ; Currents ; Roughness length ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The three dimensional linear hydrodynamic equations which describe wind induced flow in a sea are solved using the Galerkin method. A basis set of eigenfunctions is used in the calculation. These eigenfunctions are determined numerically using an expansion of B-splines.Using the Galerkin method the problem of wind induced flow in a rectangular basin is examined in detail. A no-slip bottom boundary condition with a vertically varying eddy viscosity distribution is employed in the calculation. With a low (of order 1 cm2/s) value of viscosity at the sea bed there is high current shear in this region. Viscosities of the order of 1 cm2/s) value of viscosity at the sea bed there is high current shear in this region. Viscosities of the order of 1 cm2/s near the sea bed together with high current shear in this region are physically realistic and have been observed in the sea.In order to accurately compute the eigenfunctions associated with large (of order 2000 cm2/s at the sea surface to 1 cm2/s at the sea bed) vertical variation of viscosity, an expansion of the order of thirty-five B-splines has to be used. The spline functions are distributed through the vertical so as to give the maximum resolution in the high shear region near the sea bed.Calculations show that in the case of a no-slip bottom boundary condition, with an associated region of high current shear near the sea bed, the Galerkin method with a basis set of the order of ten eigenfunctions (a Galerkin-eigenfunction method) yields an accurate solution of the hydrodynamic equations. However, solving the same problem using the Galerkin method with a basis set of B-splines, requires an expansion of the order of thirty-five spline functions in order to obtain the same accuracy.Comparisons of current profiles and time series of sea surface elevation computed using a model with a slip bottom boundary condition and a model with a no-slip boundary condition have been made. These comparisions show that consistent solutions are obtained from the two models when a physically relistic coefficient of bottom friction is used in the slip model, and a physically realistic bottom roughness length and thickness of the bottom boundary layer are employed in the no-slip model.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 17-41 
    ISSN: 0271-2091
    Keywords: Finite difference ; Hydrodynamic ; Turbulence energy ; Tidal ; Wind wave ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper deals with the numerical solution, using finite difference methods, of the hydrodynamic and turbulence energy equations which describe wind wave and tidally induced flow.Calculations are performed using staggered and non-staggered finite difference grids in the vertical, with various time discretizations of the production and dissipation terms in the turbulence energy equations. It is shown that the time discretization of these terms can significantly influence the stability of the solution. The effect of time filtering on the numerical stability of the solution is also considered. The form of the mixing length is shown to significantly influence the bed stress in wind wave problems.A no-slip condition is applied at the sea bed, and the associated high-shear bottom boundary layer is resolved by transforming the equations onto a logarithmic or log-linear co-ordinate system before applying the finite difference scheme.A computationally economic method is developed which remains stable even when a very fine vertical grid (over 200 points) is used with a time step of up to 30 min.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 101-124 
    ISSN: 0271-2091
    Keywords: Finite difference ; Spectral ; Tidal wave ; Wind wave ; Crank-Nicolson ; Logarithmic transform ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper deals with the comparative accuracy of using finite difference grids or a modal representation through the vertical in modelling tidally or wind wave induced current profiles.A point model is used in the vertical, with a no-slip condition at the sea bed. In the finite difference approach the high-shear bottom layer is resolved using either a regular grid on a logarithmic or log-linear transformed co-ordinate or an irregular grid, varying in such a manner as to retain second-order accuracy. The accuracy of these various grid schemes is considered in detail.The relative merits of using either the Crank-Nicolson or Dufort-Frankel time integration methods are considered; in the case of a fine grid in a high-viscosity region, some numerical problems are found with the Dufort-Frankel method.An alternative approach to using a finite difference grid in the vertical, namely a modal (spectral) method, is described. The form of the modes is such that they can accurately resolve the high-shear bottom boundary layer.Calculations show that the thickness of the bottom boundary layer in relation to the total water depth is important in determining the choice of grid transform and rates of convergence of solutions using finite difference or modal methods. However, for the majority of problems the modal solution is numerically attractive owing to its computational efficiency and the ease with which solution algorithms based upon it can be coded in vectorizable form suitable for the new generation of vector computers.The influence of viscosity profile, its time variation and water depth upon tidally induced or wave induced currents is considered. Calculations suggest that near-bed measurements of tidal flow in shallow water together with associated modelling would enable appropriate formulations of eddy viscosity to be determined. Similar measurements, though using a laboratory flume, would be appropriate for wind wave problems.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 1043-1072 
    ISSN: 0271-2091
    Keywords: lee-waves ; seamount ; turbulence-energy ; mixing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A three-dimensional, primitive equation, baroclinic numerical model incorporating a range of turbulence energy submodels is used to study the generation of internal lee waves over an isolated seamount. Attention is given to the turbulence mixing enhanced by the internal lee waves. The results show that regions of strong turbulence energy appear over the lee side of the seamount associated with the production of the lee waves. The computed vertical eddy viscosity and diffusivity using turbulence models can be as large as 1 m2s-1.A comparison of the magnitude and spatial distribution of the internal lee waves does not reveal any major differences in results computed using different turbulence energy models or mixing determined from a Richards on number formulation. However, the magnitude of the vertical mixing is sensitive to the form of turbulence energy submodel. Also, a study of the relevant importance of the various terms in the turbulence energy equation shows that the term representing the advection of turbulence needs to be retained in order to accurately reproduce the mixing produced by the internal lee waves. Calculations using a range of seamount profiles show that the magnitude of near-bed turbulence is sensitive to the shape of the seamount.The magnitude and spatial distribution of the lee waves and associated flow field are affected by the parametrization of horizontal diffusion, with significant differences between the use of Laplacian and biharmonic forms of horizontal diffusion. The application of biharmonic horizontal diffusion is recommended.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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