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36886 results in Cambridge Textbooks

Page 1640 of 1845

  • 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.

  • 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.

Page 1640 of 1845