Feasibility of using Lodox to perform digital subtraction angiography

Bibliography: leaves 150-157.Many cases in trauma involve vessel imaging to determine integrity and the origin of lesions or blockages. Digital subtraction angiography (DSA) is a tool used to improve the clarity of the vessels being imaged for better and easier decision making in diagnostics and planning. Lodox, a low dose x-ray system developed by Debex (Pty) Ltd, a subsidiary of de Beers, was designed specifically for the trauma environment. It therefore follows that, if possible, a function so readily used in trauma, such as DSA, should be added to the imaging repertoire of an x-ray system designed for use in this environment. In this dissertation the feasibility of using Lodox to perform DSA is therefore explored. In doing so, the requirements of a trauma unit and the theory behind DSA were researched so as to obtain a better understanding into what would be required

Image enhancement in digital X-ray angiography

Anyone who does not look back to the beginning throughout a course of action, does not look forward to the end. Hence it necessarily follows that an intention which looks ahead, depends on a recollection which looks back. | Aurelius Augustinus, De civitate Dei, VII.7 (417 A.D.) Chapter 1 Introduction and Summary D espite the development of imaging techniques based on alternative physical phenomena, such as nuclear magnetic resonance, emission of single photons ( -radiation) by radio-pharmaceuticals and photon pairs by electron-positron annihilations, re ection of ultrasonic waves, and the Doppler eect, X-ray based im- age acquisition is still daily practice in medicine. Perhaps this can be attributed to the fact that, contrary to many other phenomena, X-rays lend themselves naturally for registration by means of materials and methods widely available at the time of their discovery | a fact that gave X-ray based medical imaging an at least 50-year head start over possible alternatives. Immediately after the preliminary communica- tion on the discovery of the \new light" by R¨ ontgen [317], late December 1895, the possible applications of X-rays were investigated intensively. In 1896 alone, almost one 1,000 articles about the new phenomenon appeared in print (Glasser [119] lists all of them). Although most of the basics of the diagnostic as well as the therapeutic uses of X-rays had been worked out by the end of that year [289], research on im- proved acquisition and reduction of potential risks for humans continued steadily in the century to follow. The development of improved X-ray tubes, rapid lm changers, image intensiers, the introduction of television cameras into uoroscopy, and com- puters in digital radiography and computerized tomography, formed a succession of achievements which increased the diagnostic potential of X-ray based imaging. One of the areas in medical imaging where X-rays have always played an im- portant role is angiography,y which concerns the visualization of blood vessels in the human body. As already suggested, research on the possibility of visualization of the human vasculature was initiated shortly after the discovery of X-rays. A photograph of a rst \angiogram" | obtained by injection of a mixture of chalk, red mercury, and petroleum into an amputated hand, followed by almost an hour of exposure to X-rays | was published as early as January 1896, by Hascheck & Lindenthal [139]. Although studies on cadavers led to greatly improved knowledge of the anatomy of the human vascular system, angiography in living man for the purpose of diagnosis and intervention became feasible only after substantial progress in the development yA term originating from the Greek words o (aggeion), meaning \vessel" or \bucket", and -' (graphein), meaning \to write" or \to record". 2 1 Introduction and Summary of relatively safe contrast media and methods of administration, as well as advance- ments in radiological equipment. Of special interest in the context of this thesis is the improvement brought by photographic subtraction, a technique known since the early 1900s and since then used successfully in e.g. astronomy, but rst introduced in X-ray angiography in 1934, by Ziedses des Plantes [425, 426]. This technique al- lowed for a considerable enhancement of vessel visibility by cancellation of unwanted background structures. In the 1960s, the time consuming lm subtraction process was replaced by analog video subtraction techniques [156, 275] which, with the in- troduction of digital computers, gave rise to the development of digital subtraction angiography [194] | a technique still considered by many the \gold standard" for de- tection and quantication of vascular anomalies. Today, research on improved X-ray based imaging techniques for angiography continues, witness the recent developments in three-dimensional rotational angiography [88, 185, 186, 341,373]. The subject of this thesis is enhancement of digital X-ray angiography images. In contrast with the previously mentioned developments, the emphasis is not on the further improvement of image acquisition techniques, but rather on the development and evaluation of digital image processing techniques for retrospective enhancement of images acquired with existing techniques. In the context of this thesis, the term \enhancement" must be regarded in a rather broad sense. It does not only refer to improvement of image quality by reduction of disturbing artifacts and noise, but also to minimization of possible image quality degradation and loss of quantitative information, inevitably introduced by required image processing operations. These two aspects of image enhancement will be claried further in a brief summary of each of the chapters of this thesis. The rst three chapters deal with the problem of patient motion artifacts in digital subtraction angiography (DSA). In DSA imaging, a sequence of 2D digital X-ray projection images is acquired, at a rate of e.g. two per second, following the injection of contrast material into one of the arteries or veins feeding the part of the vasculature to be diagnosed. Acquisition usually starts about one or two seconds prior to arrival of the contrast bolus in the vessels of interest, so that the rst few images included in the sequence do not show opacied vessels. In a subsequent post-processing step, one of these \pre-bolus" images is then subtracted automatically from each of the contrast images so as to mask out background structures such as bone and soft- tissue shadows. However, it is clear that in the resulting digital subtraction images, the unwanted background structures will have been removed completely only when the patient lied perfectly still during acquisition of the original images. Since most patients show at least some physical reaction to the passage of a contrast medium, this proviso is generally not met. As a result, DSA images frequently show patient-motion induced artifacts (see e.g. the bottom-left image in Fig. 1.1), which may in uence the subsequent analysis and diagnosis carried out by radiologists. Since the introduction of DSA, in the early 1980s, many solutions to the problem of patient motion artifacts have been put forward. Chapter 2 presents an overview of the possible types of motion artifacts reported in the literature and the techniques that have been proposed to avoid them. The main purpose of that chapter is to review and discuss the techniques proposed over the past two decades to correct for 1 Introduction and Summary 3 Figure 1.1. Example of creation and reduction of patient motion artifacts in cerebral DSA imaging. Top left: a \pre-bolus" or mask image acquired just prior to the arrival of the contrast medium. Top right: one of the contrast or live images showing opacied vessels. Bottom left: DSA image obtained after subtraction of the mask from the contrast image, followed by contrast enhancement. Due to patient motion, the background structures in the mask and contrast image were not perfectly aligned, as a result of which the DSA image does not only show blood vessels, but also additional undesired structures (in this example primarily in the bottom-left part of the image). Bottom right: DSA image resulting from subtraction of the mask and contast image after application of the automatic registration algorithm described in Chapter 3. 4 1 Introduction and Summary patient motion artifacts retrospectively, by means of digital image processing. The chapter addresses fundamental problems, such as whether it is possible to construct a 2D geometrical transformation that exactly describes the projective eects of an originally 3D transformation, as well as practical problems, such as how to retrieve the correspondence between mask and contrast images by using only the grey-level information contained in the images, and how to align the images according to that correspondence in a computationally ecient manner. The review in Chapter 2 reveals that there exists quite some literature on the topic of (semi-)automatic image alignment, or image registration, for the purpose of motion artifact reduction in DSA images. However, to the best of our knowledge, research in this area has never led to algorithms which are suciently fast and robust to be acceptable for routine use in clinical practice. By drawing upon the suggestions put forward in Chapter 2, a new approach to automatic registration of digital X-ray angiography images is presented in Chapter 3. Apart from describing the functionality of the components of the algorithm, special attention is paid to their computationally optimal implementation. The results of preliminary experiments described in that chapter indicate that the algorithm is eective, very fast, and outperforms alterna- tive approaches, in terms of both image quality and required computation time. It is concluded that the algorithm is most eective in cerebral and peripheral DSA imag- ing. An example of the image quality enhancement obtained after application of the algorithm in the case of a cerebral DSA image is provided in Fig 1.1. Chapter 4 reports on a clinical evaluation of the automatic registration technique. The evaluation involved 104 cerebral DSA images, which were corrected for patient motion artifacts by the automatic technique, as well as by pixel shifting | a manual correction technique currently used in clinical practice. The quality of the DSA images resulting from the two techniques was assessed by four observers, who compared the images both mutually and to the corresponding original images. The results of the evaluation presented in Chapter 4 indicate that the dierence in performance between the two correction techniques is statistically signicant. From the results of the mutual comparisons it is concluded that, on average, the automatic registration technique performs either comparably, better than, or even much better than manual pixel shifting in 95% of all cases. In the other 5% of the cases, the remaining artifacts are located near the borders of the image, which are generally diagnostically non-relevant. In addition, the results show that the automatic technique implies a considerable reduction of post-processing time compared to manual pixel shifting (on average, one second versus 12 seconds per DSA image). The last two chapters deal with somewhat dierent topics. Chapter 5 is concerned with visualization and quantication of vascular anomalies in three-dimensional rota- tional angiography (3DRA). Similar to DSA imaging, 3DRA involves the acquisition of a sequence of 2D digital X-ray projection images, following a single injection of contrast material. Contrary to DSA, however, this sequence is acquired during a 180 rotation of the C-arch on which the X-ray source and detector are mounted antipo- dally, with the object of interest positioned in its iso-center. The rotation is completed in about eight seconds and the resulting image sequence typically contains 100 images, which form the input to a ltered back-projection algorithm for 3D reconstruction. In contrast with most other 3D medical imaging techniques, 3DRA is capable of provid- 1 Introduction and Summary 5 Figure 1.2. Visualizations of a clinical 3DRA dataset, illustrating the qualitative improvement obtained after noise reduction ltering. Left: volume rendering of the original, raw image. Right: volume rendering of the image after application of edge-enhancing anisotropic diusion ltering (see Chapter 5 for a description of this technique). The visualizations were obtained by using the exact same settings for the parameters of the volume rendering algorithm. ing high-resolution isotropic datasets. However, due to the relatively high noise level and the presence of other unwanted background variations caused by surrounding tissue, the use of noise reduction techniques is inevitable in order to obtain smooth visualizations of these datasets (see Fig. 1.2). Chapter 5 presents an inquiry into the eects of several linear and nonlinear noise reduction techniques on the visualization and subsequent quantication of vascular anomalies in 3DRA images. The evalua- tion is focussed on frequently occurring anomalies such as a narrowing (or stenosis) of the internal carotid artery or a circumscribed dilation (or aneurysm) of intracra- nial arteries. Experiments on anthropomorphic vascular phantoms indicate that, of the techniques considered, edge-enhancing anisotropic diusion ltering is most suit- able, although the practical use of this technique may currently be limited due to its memory and computation-time requirements. Finally, Chapter 6 addresses the problem of interpolation of sampled data, which occurs e.g. when applying geometrical transformations to digital medical images for the purpose of registration or visualization. In most practical situations, interpola- tion of a sampled image followed by resampling of the resulting continuous image on a geometrically transformed grid, inevitably implies loss of grey-level information, and hence image degradation, the amount of which is dependent on image content, but also on the employed interpolation scheme (see Fig. 1.3). It follows that the choice for a particular interpolation scheme is important, since it in uences the re- sults of registrations and visualizations, and the outcome of subsequent quantitative analyses which rely on grey-level information contained in transformed images. Al- though many interpolation techniques have been developed over the past decades, 6 1 Introduction and Summary Figure 1.3. Illustration of the fact that the loss of information due to interpola- tion and resampling operations is dependent on the employed interpolation scheme. Left: slice of a 3DRA image after rotation over 5:0, by using linear interpolation. Middle: the same slice, after rotation by using cubic spline interpolation. Right: the dierence between the two rotated images. Although it is not possible with such a comparison to come to conclusions as to which of the two methods yields the smallest loss of grey-level information, this example clearly illustrates the point that dierent interpolation methods usually yield dierent results. thorough quantitative evaluations and comparisons of these techniques for medical image transformation problems are still lacking. Chapter 6 presents such a compar- ative evaluation. The study is limited to convolution-based interpolation techniques, as these are most frequently used for registration and visualization of medical image data. Because of the ubiquitousness of interpolation in medical image processing and analysis, the study is not restricted to XRA and 3DRA images, but also includes datasets from many other modalities. It is concluded that for all modalities, spline interpolation constitutes the best trade-o between accuracy and computational cost, and therefore is to be preferred over all other methods. In summary, this thesis is concerned with the improvement of image quality and the reduction of image quality degradation and loss of quantitative information. The subsequent chapters describe techniques for reduction of patient motion artifacts in DSA images, noise reduction techniques for improved visualization and quantication of vascular anomalies in 3DRA images, and interpolation techniques for the purpose of accurate geometrical transformation of medical image data. The results and con- clusions of the evaluations described in this thesis provide general guidelines for the applicability and practical use of these techniques

Stability and Seakeeping of Marine Vessels

This book presents the papers accepted into the Special Issue “Stability and Seakeeping of Marine Vessels” and includes nine contributions to this Special Issue published in 2020. The overall aim of the collection is to improve knowledge about the most relevant and recent topics in ship stability and seakeeping. Specifically, the articles cover a wide range of topics and reflect the recent scientific efforts in the 2nd generation intact stability criteria evaluation and modelling of the ship dynamics assessment in intact or damaged conditions. These topics were investigated mainly through direct assessments performed both via numerical methods and tools, and experimental approaches. The book is addressed to individuals from universities, research organizations, industry, government agencies and certifying authorities, as well as designers, operators and owners who contribute to improved knowledge about “stability and seakeeping”

Integration of anatomical and hemodynamical information in magnetic resonance angiography

+118hlm.;24c

Self-adaptive isogeometric spatial discretisations of the first and second-order forms of the neutron transport equation with dual-weighted residual error measures and diffusion acceleration

As implemented in a new modern-Fortran code, NURBS-based isogeometric analysis (IGA) spatial discretisations and self-adaptive mesh refinement (AMR) algorithms are developed in the application to the first-order and second-order forms of the neutron transport equation (NTE). These AMR algorithms are shown to be computationally efficient and numerically accurate when compared to standard approaches. IGA methods are very competitive and offer certain unique advantages over standard finite element methods (FEM), not least of all because the numerical analysis is performed over an exact representation of the underlying geometry, which is generally available in some computer-aided design (CAD) software description. Furthermore, mesh refinement can be performed within the analysis program at run-time, without the need to revisit any ancillary mesh generator. Two error measures are described for the IGA-based AMR algorithms, both of which can be employed in conjunction with energy-dependent meshes. The first heuristically minimises any local contributions to the global discretisation error, as per some appropriate user-prescribed norm. The second employs duality arguments to minimise important local contributions to the error as measured in some quantity of interest; this is commonly known as a dual-weighted residual (DWR) error measure and it demands the solution to both the forward (primal) and the adjoint (dual) NTE. Finally, convergent and stable diffusion acceleration and generalised minimal residual (GMRes) algorithms, compatible with the aforementioned AMR algorithms, are introduced to accelerate the convergence of the within-group self-scattering sources for scattering-dominated problems for the first and second-order forms of the NTE. A variety of verification benchmark problems are analysed to demonstrate the computational performance and efficiency of these acceleration techniques.Open Acces

Geometric data understanding : deriving case specific features

There exists a tradition using precise geometric modeling, where uncertainties in data can be considered noise. Another tradition relies on statistical nature of vast quantity of data, where geometric regularity is intrinsic to data and statistical models usually grasp this level only indirectly. This work focuses on point cloud data of natural resources and the silhouette recognition from video input as two real world examples of problems having geometric content which is intangible at the raw data presentation. This content could be discovered and modeled to some degree by such machine learning (ML) approaches like deep learning, but either a direct coverage of geometry in samples or addition of special geometry invariant layer is necessary. Geometric content is central when there is a need for direct observations of spatial variables, or one needs to gain a mapping to a geometrically consistent data representation, where e.g. outliers or noise can be easily discerned. In this thesis we consider transformation of original input data to a geometric feature space in two example problems. The first example is curvature of surfaces, which has met renewed interest since the introduction of ubiquitous point cloud data and the maturation of the discrete differential geometry. Curvature spectra can characterize a spatial sample rather well, and provide useful features for ML purposes. The second example involves projective methods used to video stereo-signal analysis in swimming analytics. The aim is to find meaningful local geometric representations for feature generation, which also facilitate additional analysis based on geometric understanding of the model. The features are associated directly to some geometric quantity, and this makes it easier to express the geometric constraints in a natural way, as shown in the thesis. Also, the visualization and further feature generation is much easier. Third, the approach provides sound baseline methods to more traditional ML approaches, e.g. neural network methods. Fourth, most of the ML methods can utilize the geometric features presented in this work as additional features.Geometriassa käytetään perinteisesti tarkkoja malleja, jolloin datassa esiintyvät epätarkkuudet edustavat melua. Toisessa perinteessä nojataan suuren datamäärän tilastolliseen luonteeseen, jolloin geometrinen säännönmukaisuus on datan sisäsyntyinen ominaisuus, joka hahmotetaan tilastollisilla malleilla ainoastaan epäsuorasti. Tämä työ keskittyy kahteen esimerkkiin: luonnonvaroja kuvaaviin pistepilviin ja videohahmontunnistukseen. Nämä ovat todellisia ongelmia, joissa geometrinen sisältö on tavoittamattomissa raakadatan tasolla. Tämä sisältö voitaisiin jossain määrin löytää ja mallintaa koneoppimisen keinoin, esim. syväoppimisen avulla, mutta joko geometria pitää kattaa suoraan näytteistämällä tai tarvitaan neuronien lisäkerros geometrisia invariansseja varten. Geometrinen sisältö on keskeinen, kun tarvitaan suoraa avaruudellisten suureiden havainnointia, tai kun tarvitaan kuvaus geometrisesti yhtenäiseen dataesitykseen, jossa poikkeavat näytteet tai melu voidaan helposti erottaa. Tässä työssä tarkastellaan datan muuntamista geometriseen piirreavaruuteen kahden esimerkkiohjelman suhteen. Ensimmäinen esimerkki on pintakaarevuus, joka on uudelleen virinneen kiinnostuksen kohde kaikkialle saatavissa olevan datan ja diskreetin geometrian kypsymisen takia. Kaarevuusspektrit voivat luonnehtia avaruudellista kohdetta melko hyvin ja tarjota koneoppimisessa hyödyllisiä piirteitä. Toinen esimerkki koskee projektiivisia menetelmiä käytettäessä stereovideosignaalia uinnin analytiikkaan. Tavoite on löytää merkityksellisiä paikallisen geometrian esityksiä, jotka samalla mahdollistavat muun geometrian ymmärrykseen perustuvan analyysin. Piirteet liittyvät suoraan johonkin geometriseen suureeseen, ja tämä helpottaa luonnollisella tavalla geometristen rajoitteiden käsittelyä, kuten väitöstyössä osoitetaan. Myös visualisointi ja lisäpiirteiden luonti muuttuu helpommaksi. Kolmanneksi, lähestymistapa suo selkeän vertailumenetelmän perinteisemmille koneoppimisen lähestymistavoille, esim. hermoverkkomenetelmille. Neljänneksi, useimmat koneoppimismenetelmät voivat hyödyntää tässä työssä esitettyjä geometrisia piirteitä lisäämällä ne muiden piirteiden joukkoon

Towards Forecasting Capability in Solar Energetic Particle Modeling

Solar Energetic Particles (SEPs) are an important aspect of space weather. SEP events posses a high destructive potential, since they may cause disruptions of communication systems on Earth and be fatal to crew members onboard spacecrafts and, in extreme cases, harmful to people onboard high altitude flights. However, currently the research community lacks efficient tools to predict such hazardous threat and its potential impacts. Such a tool is a first step for humanity to improve its preparedness for SEP events and ultimately to be able to mitigate their effects. The main goal of this project is to develop a computational tool that will have the forecasting capability and can be the basis for operational system that will provide live information on the current potential threats posed by SEP based on the observations of the Sun. The complexity of the problem is reflected in the level of sophistication of the product of development. The tool comprises several numerical models, which are designed to simulate different physical aspects of SEPs. The background conditions in the interplanetary medium, the magnetic field in particular, play a defining role in the transport and acceleration of SEPs, and are simulated with the state-of-the-art MHD solver, BATS-R-US. The newly developed particle code, M-FLAMPA, simulates the actual transport and acceleration of SEPs and is coupled to the MHD code. The special property of SEPs, the tendency to follow magnetic lines of force, is fully taken advantage of in the computational model, which substitutes a complicated 3-D model with a multitude of 1-D models. This approach significantly simplifies computations and improves the time performance of the overall model. Another aspect of SEP physics, the production of energetic particles during solar flares is also explored.PHDAtmospheric, Oceanic & Space ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138463/1/dborovik_1.pd