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38504 results in Cambridge Textbooks

Page 1721 of 1926

  • 13 - Medical applications of imaging

  • 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 381-394

  • Summary

    Overview

    Imaging science visualizes an object and quantitatively characterizes its structure and/or function. Biomedical imaging applies imaging science to the presentation of and interaction with multi-modality biomedical images with a view to using them productively to examine and diagnose disease in human patients. This chapter discusses a number of specific applications in medicine that illustrate many of the concepts introduced in this book. The examples have been chosen to demonstrate a wide range of algorithms and approaches; none represent complete solutions, but are rather examples of continuing research.

    Learning objectives

    After reading this chapter you will be able to:

  • • appreciate the complexity and problems associated with imaging tasks;

  • • recognize broad schemes for approaching image analysis;

  • • analyze the component parts in an imaging problem;

  • • select potential strategies for analyzing images from a variety of applications.

    • Computer-aided diagnosis in mammography

    Mammography (Section 3.2.3) is the single most important technique in the investigation of breast cancer, the most common malignancy in women. It can detect disease at an early stage when therapy or surgery is most effective. However the interpretation of screening mammograms is a repetitive task involving subtle signs, and suffers from a high rate of false negatives (10–30% of women with breast cancer are falsely told that they are free of the disease on the basis of their mammograms (Martin, Moskowitz and Milbrath, 1979)), and false positives (only 10–20% of masses referred for surgical biopsy are actually malignant (Kopans, 1992)). Computer-aided diagnosis (CAD) aims to increase the predictive value of the technique by pre-reading mammograms to indicate the locations of suspicious abnormalities, and analyze their characteristics, as an aid to the radiologist.

  • 4 - Medical images obtained with non-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 90-120

  • Summary

    Overview

    Diagnostic medical ultrasound uses high-frequency sound and a simple pulse–echo technique. When an ultrasound beam is swept across a volume of interest, a crosssectional image can be formed from a mapping of echo intensities. Current medical ultrasound imaging systems are based on envelope detection, and therefore only display intensity information. Despite this shortcoming, ultrasound imaging has become an important and widely accepted modality for non-invasive imaging of the human body because of its ability to produce real-time images, its low cost and its low risk to the patient. Magnetic resonance imaging (MRI) uses the phenomenon of nuclear magnetic resonance (NMR): unpaired nucleons, such as protons, orientate themselves in a magnetic field, and radiofrequency pulses can be used to change the balance of the orientations. When the system returns to equilibrium it produces signals that can be used to produce an image, which is characterized by its high contrast for soft tissues. MRI images map function, as well as structure. Digital images from any imaging modality can be compared or combined, after image registration, using a networking system.

    Learning objectives

    After reading this chapter you will be able to:

  • • explain the basis of imaging using non-ionizing radiation, specifically ultrasound and radiofrequency (RF) radiation with a strong magnetic field;

  • • outline the physical factors involved in these imaging modalities;

  • • describe the factors which determine the speed of ultrasound waves in a material;

  • • explain the purpose of time gain compensation and describe how it is implemented;

  • • summarize the steps involved in the reconstruction of B-mode ultrasound images;

  • • identify the factors that affect image quality and artifacts in ultrasound imaging;

  • • describe the phenomenon of nuclear magnetic resonance (NMR);

  • • explain how MRI images can be constructed from NMR spectra;

  • • describe the use of magnetic field gradients to add spatial information to MRI images;

  • • summarize the changes that occur to the spins using the spin echo pulse sequence;

  • • identify the factors that affect image quality and artifacts in MRI imaging;

  • • describe how functional information can be obtained from MRI imaging;

  • • summarize the advantages of a picture, archiving and communications system (PACS);

  • • outline the factors involved in the co-registration of images from different modalities.

  • 8 - Image restoration

  • 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 246-270

  • Summary

    Overview

    An image is never an exact representation of the object under observation; it is always corrupted by degradations during acquisition and within the imaging system itself. These include noise, blurring and distortion. Image restoration removes or reduces these degradations. The point spread function (PSF) or the modulation transfer function (MTF) provides a complete, quantitative description of an imaging system and directly characterizes the image degradation within the system and can be used to restore the fine detail in images. The problem is more complicated if the image is also degraded by significant amounts of noise. Restoration techniques attempt to model the degradation and apply the inverse process to recover the original image. They are most effective when the point spread function or modulation transfer function is known and the nature of the blurring and noise are well understood. Geometric distortions can be reversed using inverse bilinear equations and gray-level interpolation.

    Learning objectives

    After reading this chapter you will be able to:

  • • identify the main sources of image noise and discuss their characteristics;

  • • choose appropriate general strategies for minimizing the effects of noise;

  • • discuss the advantages of adaptive filtering;

  • • model image degradation comprising blur and additive noise;

  • • employ suitable values to Wiener filter a noisy, blurred image;

  • • compare the performance of inverse filtering with Wiener filtering;

  • • explain how distortion can be removed from images.

    • Image degradation

    Images can be degraded by a number of different mechanisms, including noise, blurring and distortion. Noise is present because any imaging device must use a finite exposure (or integration) time, which introduces stochastic noise from the random arrival of photons. Optical imperfections and instrumentation noise (for example, thermal noise in CCD devices) result in more noise. Sampling causes noise due to aliasing of high-frequency signal components, and digitization produces quantization errors. Further noise can be introduced by communication errors and compression. Blurring is present in any imaging system which uses electromagnetic radiation (for example, visible light and x-rays).

  • Chapter 1 - Antecedents

  • from Part I - The Ocean Shall Unloose the Bonds of Things
  • Thomas Benjamin, Central Michigan University
  • Book:
    The Atlantic World
    Published online:
    01 February 2019
    Print publication:
    16 February 2009, pp 6-51

  • Summary

    Before the fifteenth century, the lands touching the Atlantic Ocean were different worlds, separate and largely isolated, unknown or mostly unknown one to the others. There had been no earlier traveler, no Marco Polo, to demonstrate the connections and networks that could and, in time, would tie these distant lands together. The same ocean that soon became a vast crossroads bringing peoples together had constituted the ultimate barrier for millennia. With the sea at their backs, societies had turned their attention inward, not out. Cultures that one day would cooperate and clash emerged and evolved in different ways on different continents. Their histories followed exceptional courses and their peoples, of course, were unaware of any Atlantic destiny. Out of this diversity, a new circuit would be knitted and forged, the Atlantic World. “The Atlantic, once the end of the world,” writes Barry Cunliffe, “was now the beginning.” To understand the making of the Atlantic World, we must first examine its components and antecedents. We turn to the distant and separate worlds of the Atlantic rim: the Americas, Africa and Europe on the eve of the European voyages of exploration and expansion.

    The Americas

    The very concepts of America, Africa and Europe are products of the Europeanization of world geography. Before the Florentine navigator Amerigo Vespucci lent his name to the northern and southern continents of the Western Hemisphere, the native peoples did not conceive of themselves as Americans or Indians.

  • Chapter 10 - Rivals

  • from Part III - A New Order of the Ages
  • Thomas Benjamin, Central Michigan University
  • Book:
    The Atlantic World
    Published online:
    01 February 2019
    Print publication:
    16 February 2009, pp 472-516

  • Summary

    During the long eighteenth century, from 1689 until 1815, the Atlantic was the arena of a titanic conflict between France and Great Britain. During this second hundred years' war, these rivals expanded their conflicts from Europe itself into the Atlantic and Asia. In the Atlantic, their conflicts had enormous repercussions. France lost its North American Empire during the French and Indian War in the early 1760s while Great Britain sowed the seeds of independence in its North American seaboard colonies. The American war of independence was successful in large part because of an American alliance with France and France's war with Britain. France's debt from this conflict helped provoke the crisis that initiated the French Revolution in 1789, which, in turn, brought more than two decades of war to Europe. The wars of the French Revolution and Empire created the necessary context for the slave revolution in French Saint Domingue in the 1790s and the independence of Haiti in 1804 as well as the revolutions for independence of Spanish America and Brazil. The great Anglo-French wars of the long eighteenth century transformed the Atlantic World.

    In this great power rivalry Indians and Africans were often critical participants. The struggle for North America placed Native American nations in the middle of French and British imperial ambitions, which meant that they held the balance of power and, to a considerable extent, could determine who won or lost.

  • Chapter 12 - Equality

  • from Part III - A New Order of the Ages
  • Thomas Benjamin, Central Michigan University
  • Book:
    The Atlantic World
    Published online:
    01 February 2019
    Print publication:
    16 February 2009, pp 567-614

  • Summary

    From 1811 to 1815 the popular Republic of Cartagena, comprised of the Caribbean port city and its province, became one of the first republics of the hemisphere that guaranteed equal political rights to free pardos (blacks and mulattos) and whites. The armed people of the lower-class neighborhood of Getsemaní forced the hesitant Creole elite of the city to declare independence from Spain. Royalist observer Fernández de Santos noted that Cartageñeros had become “enchanted with the promises of happiness and frenetic egalitarianism.” The revolutions that continued to break out in the Atlantic World after 1776 and 1789, particularly in Saint Domingue, New Spain and elsewhere in Spanish America, were in substantial part egalitarian revolutions that arose within the basic framework of liberal constitutional revolutions. Pardos and Indians claimed and fought for equality with whites. They were inspired by the struggle of white Creoles to attain equality with Europeans. The Spanish American revolutionary Simón Bolívar, however, saw a powerful contradiction at work: “The rich will not tolerate democracy, nor will the slaves and free pardos tolerate aristocracy. The rich would prefer the tyranny of a single individual, so as not to suffer the violence of the mob, and also to establish a somewhat peaceful order.” In societies of considerable inequality, liberal revolutions faced great obstacles.

    The revolutions of the age were unquestionably Atlantic phenomena. The revolution of the slaves in Saint Domingue in the 1790s and early 1800s, the Haitian Revolution, was an unwanted product of the French Revolution.

  • Chapter 6 - Engagement

  • from Part II - Europe Supported by Africa and America
  • Thomas Benjamin, Central Michigan University
  • Book:
    The Atlantic World
    Published online:
    01 February 2019
    Print publication:
    16 February 2009, pp 273-325

  • Summary

    “Atlantic America was the scene of a vast unplanned, uncontrolled, unstable, and unending encounter between European and Indian societies.” D. W. Meinig's characterization of European-Indian relations is descriptive and evocative. What began in 1492 was an encounter and collision between Indians and Europeans as well as a sustained engagement among exceedingly diverse peoples for hundreds of years. Engagement meant mutual adaptation and conflict, alliance and conquest, and acculturation as a two-way interaction. Natives and Europeans were entangled with each other, that is, they were intricately intertwined in ways that transformed both. This complex engagement between two diverse groups of peoples over hundreds of years constitutes one of the most important themes in the history of the Atlantic World.

    Because Indian populations, cultures and societies varied considerably, as did Europeans and their objectives, Native American and European entanglements were often quite different and distinct from place to place, creating different kinds of outcomes. A few broad patterns emerged. Large and complex native societies such as those in Mesoamerica and the Central Andes experienced military conquests and political subordination. Here Euroamerican conquest colonies incorporated Indian populations and cultures within complex hierarchical and multicultural societies. Where invading agricultural settlers sought the land of small-scale and decentralized native farming societies (generally on the coasts of South and North America), conflict was almost perpetual until the resisting native peoples were defeated, dispersed or placed in “pacified” enclaves within the colonial boundaries.

Page 1721 of 1926