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38504 results in Cambridge Textbooks

Page 1720 of 1926

  • Preface

  • Augustus, Alison E. Cooley, University of Warwick
  • Book:
    <I>Res Gestae Divi Augusti</I>
    Published online:
    28 May 2018
    Print publication:
    14 May 2009, pp xi-xi

  • Summary

    I'm glad to be able to take this opportunity to thank Graham Oliver, whose enthusiastic and congenial collaboration over a paper for the Triennial Conference on the RGDA initially inspired the idea of undertaking this project. I'd also like to acknowledge the role played by my students at Warwick, notably the three cohorts who have grappled the Augustan age with me, who often make me clarify my ideas, and generally help inspire me by their enthusiasm for the subject. Michael Sharp has been supportive of the book from start to finish, offering invaluable practical help. Three Cambridge University Press assessors made helpful suggestions in planning the shape of the book in its infancy; Stephen Mitchell and the other Cambridge University Press reader provided copious suggestions for guiding the original typescript towards maturity; I hope that they like what they find now. Any faults in the book remain the result of my oversight or stubbornness. For help in compiling the illustrations I'm indebted to Michael Sharp, Stephen Mitchell, and my father. I'm grateful to Richard Abdy of the British Museum for permission to reproduce some of the images of coins already to be found in the LACTOR sourcebook, The Age of Augustus, ed. M. G. L. Cooley. Family support has been crucial, and I'm incredibly fortunate to have such tolerant children, husband, parents, and mother-in-law. Among other things, I'd single out the constructive criticism and practical help from Melvin and my parents, and the innumerable hours of childcare undertaken by my mother-in-law.

  • 14 - Frontiers of image processing in medicine

  • from Part IV - Medical applications and ongoing developments
  • Geoff Dougherty
  • Book:
    Digital Image Processing for Medical Applications
    Published online:
    12 September 2018
    Print publication:
    09 April 2009, pp 395-398

  • Summary

    Overview

    The recent rapid advances in medical imaging and automated image analysis will continue and allow us to make significant advances in our understanding of life and disease processes, and our ability to deliver quality healthcare. A few of the synergistic developments involving a number of disciplines are highlighted.

    Learning objectives

    After reading this chapter you will be able to:

  • • recognize the limitations of current imaging technology;

  • • appreciate the trends and ongoing developments in medical imaging.

    • Trends

    “A picture is worth a thousand words.”

    The rapid advances of the last two or three decades in medical imaging technology, which have delivered high-resolution, three-dimensional anatomical and physiological images, is continuing apace, enabling ever more powerful advances in diagnosis and intervention. Improved, miniature detectors are pushing spatial resolution below 1 mm, which will require large computer memories and storage capacities and improved software capabilities to visualize the larger data sets interactively. Advances in post-processing, especially in automated registration, segmentation, classification and rendering, will be required (Van Leemput et al., 1999; Huber and Hebert, 2003; Way et al., 2006). The availability of multimodality imaging, such as combined CT/PET scanners, is increasing, along with the means to share such images around the clinical setting and remotely, fueling improvements in PACS and telemedicine systems (Section 4.3).

    The inverse problem

    A basic aspect of most imaging modalities is to reconstruct an image based on minimally invasive measurements from a number of sensors. The inverse problem determines the properties of the unknown system from the observed measurements. The goal of the reconstruction can be either structural information, such as the anatomy that comes from CT or MRI imaging, or functional information from nuclear medicine imaging or electrical impedance tomography (EIT). An important key feature of inverse problems is their ill-posedness, i.e. they do not fulfil classical requirements of existence, uniqueness and stability under data perturbations. The last aspect is especially important since in the real world measurements always contain noise; approximation methods for solving inverse problems with minimal sensitivity to noise, so-called regularization methods, are being studied.

  • 7 - Image enhancement in the frequency domain

  • from Part II - Fundamental concepts of image processing
  • Geoff Dougherty
  • Book:
    Digital Image Processing for Medical Applications
    Published online:
    12 September 2018
    Print publication:
    09 April 2009, pp 194-245

  • Summary

    Overview

    A number of mathematical transformations can be applied to images to obtain information that is not readily available in the raw image. The Fourier transform is the most popular although other transforms, such as wavelets and the Gabor transform, are being increasingly used. The Fourier transform converts the spatial domain representation of an image into an alternative representation in the Fourier domain, in terms of spatial frequencies. Convolution of the input data with the point spread function of an imaging system results in the formation of an image. The convolution operation in the spatial domain is equivalent to multiplication in the Fourier domain, which is a more efficient method of performing smoothing or sharpening of an image.

    Learning objectives

    After reading this chapter you will be able to:

  • • describe how periodic waveforms consist of a linear superposition of sinusoids;

  • • explain how the Fourier transform is derived from the Fourier series;

  • • illustrate the concept of the discrete Fourier transform in two dimensions, with its dependence on sample and hold;

  • • describe the phenomenon of aliasing and apply appropriate procedures to eliminate it;

  • • outline the properties of the Fourier transform;

  • • use cross-correlation to perform template matching;

  • • obtain the spatial resolution of an imaging system both from its point spread function (PSF) and from its modulation transfer function (MTF), and show that they are equivalent;

  • • use frequency domain filters to smooth or sharpen an image while avoiding ringing artifacts;

  • • explain the need for filters in filtered backprojection and summarize the filtered backprojection algorithm;

  • • outline the properties of the Radon transform;

  • • describe the process of direct Fourier reconstruction.

    • The Fourier domain

    Although the convolution process provides a model for the formation of an image from input signals by a (linear shift-invariant) imaging system, there exists an alternative and equivalent way of modeling the process in terms of the spatial frequency content of the image. Spatial frequency is a measure of how frequently gray values change over distance.

  • 1 - Introduction

  • from Part I - Introduction to image processing
  • Geoff Dougherty
  • Book:
    Digital Image Processing for Medical Applications
    Published online:
    12 September 2018
    Print publication:
    09 April 2009, pp 3-15

  • Summary

    Overview

    Imaging systems construct an (output) image in response to (input) signals from diverse types of objects. They can be classified in a number of ways, e.g. according to the radiation or field used, the property being investigated, or whether the images are formed directly or indirectly. Medical imaging systems, for example, take input signals which arise from various properties of the body of a patient, such as its attenuation of x-rays or reflection of ultrasound. The resulting images can be continuous, i.e. analog, or discrete, i.e. digital; the former can be converted into the latter by digitization. The challenge is to obtain an output image that is an accurate representation of the input signal, and then to analyze it and extract as much diagnostic information from the image as possible.

    Learning objectives

    After reading this chapter you will be able to:

  • • appreciate the breadth and scope of digital image processing;

  • • classify imaging systems according to different criteria;

  • • distinguish between analog, sampled and digital images;

  • • identify the advantages of digital imaging;

  • • describe the components of a generic digital image processing system;

  • • outline the operations involved in the various fundamental classes of image processing;

  • • list examples of digital image processing applications within a variety of fields.

    • Imaging systems

    Of the five senses – sight, hearing, touch, smell and taste – which humans use to perceive their environment, sight is the most powerful. Receiving and analyzing images forms a large part of the routine cerebral activity of human beings throughout their waking lives. In fact, more than 99% of the activity of the human brain is involved in processing images from the visual cortex. Avisual image is rich in information. Confucius said, “A picture is worth a thousand words,” and we shall see that that is an underestimate.

  • Preface

  • Geoff Dougherty
  • Book:
    Digital Image Processing for Medical Applications
    Published online:
    12 September 2018
    Print publication:
    09 April 2009, pp ix-xii

  • Summary

    The influence and impact of digital images on modern society, science, technology and art are tremendous. Image processing has become such a critical component in contemporary science and technology that many tasks would not be attempted without it. It is a truly interdisciplinary subject that draws from synergistic developments involving many disciplines and is used in medical imaging, microscopy, astronomy, computer vision, geology and many other fields.

    The rapid and continuing progress in computerized medical image reconstruction, and the associated developments in analysis methods and computer-aided diagnosis, have propelled medical imaging into one of the most important sub-fields in scientific imaging. This book takes its motivation from medical applications and uses real medical images and situations to clarify and consolidate concepts and to build intuition, insight and understanding. An overview of the fundamentals of the most important clinical imaging modalities in use is included to provide a context, and to illustrate how the images are produced and acquired.

    This is a text for use in a first practical course in image processing and analysis, for final-year undergraduate or first-year graduate students with a background in biomedical engineering, computer science, radiologic sciences or physics. Designed for readers who will become “end users” of digital image processing in the biomedical sciences, it emphasizes the conceptual framework and the effective use of image processing tools and uses mathematics as a tool, minimizing the advanced mathematical development of other textbooks.

    Discussions of the major medical imaging modalities enable students to understand the diagnostic tasks for which images are needed and the typical distortions and artifacts associated with each modality. This knowledge then motivates the presentation of the techniques needed to reverse distortions, minimize artifacts and enhance important features. Students understand why they are undertaking particular operations, and the practical activities enable them to see in real time how operations affect real images. Image processing is a hands-on discipline, and the best way to learn is by doing. Theory and practice are linked, each reinforcing the other.

  • 3 - Medical images obtained with ionizing radiation

  • from Part I - Introduction to image processing
  • Geoff Dougherty
  • Book:
    Digital Image Processing for Medical Applications
    Published online:
    12 September 2018
    Print publication:
    09 April 2009, pp 47-89

  • Summary

    Overview

    The introduction of advanced imaging modalities has significantly improved the diagnostic information available to physicians. Computer technology has enabled tomographic and three-dimensional reconstruction of images, illustrating both anatomical features (using x-rays) and physiological functioning (using γ-rays emitted from ingested or injected radioactive tracers), free from overlying structures. Since both x-rays and γ-rays are forms of ionizing radiation, they must be used prudently in order to minimize damage to the body and its genetic material.

    Learning objectives

    After reading this chapter you will be able to:

  • • explain the basis of imaging using x-rays and γ-rays;

  • • outline the physical factors involved in imaging modalities using ionizing radiation;

  • • identify the factors that affect image quality in imaging systems that use ionizing radiation;

  • • explain the advantages of computed radiography over film radiography;

  • • describe the specific challenges in mammography and explain how they are addressed;

  • • describe the imaging pathway in fluoroscopy;

  • • explain the advantages and limitations of digital subtraction angiography;

  • • distinguish planar imaging from topographic imaging;

  • • reconstruct a simple x-ray tomographic image using backprojection;

  • • explain how the production of a tomographic image in single-photon emission tomography (SPECT) differs from that in x-ray computed tomography (CT);

  • • identify the organs and tissues most sensitive to damage by ionizing radiation.

    • Medical imaging modalities

    Medical imaging systems detect different physical signals arising from a patient and produce images. An imaging modality is an imaging system which uses a particular technique. Some of these modalities use ionizing radiation, radiation with sufficient energy to ionize atoms and molecules within the body, and others use non-ionizing radiation. Ionizing radiation in medical imaging comprises x-rays and γ-rays, both of which need to be used prudently to avoid causing serious damage to the body and to its genetic material. Non-ionizing radiation, on the other hand, does not have the potential to damage the body directly and the risks associated with its use are considered to be very low. Examples of such radiation are ultrasound, i.e. high-frequency sound, and radio frequency waves.

Page 1720 of 1926