Principles of CT II
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Questions and Answers

What information is assigned to each pixel in a reconstructed CT image?

  • CT numbers or Hounsfield units (correct)
  • Linear attenuation coefficients (μ) of the tissues
  • Attenuation coefficients and CT numbers for common tissues
  • All of the above

    • Who is the inventor of CT technology, after whom Hounsfield units are named?

  • S. Jastaniah
  • A. Aref
  • J. Al-Ghamdi
  • Sir Godfrey Hounsfield (correct)

    • What is the mathematical relationship between linear attenuation coefficients and CT numbers?

  • CT number = μ - 1000
  • CT number = μ + 1000 (correct)
  • CT number = μ / 1000
  • CT number = 1000 + μ

    • What is the unit of measurement for linear attenuation coefficients?

    <p>μ (mu)</p> Signup and view all the answers

    What are CT numbers related to?

    <p>Linear attenuation coefficients of the tissues</p> Signup and view all the answers

    What is the significance of Sir Godfrey Hounsfield in CT technology?

    <p>He invented CT technology</p> Signup and view all the answers

    What is the purpose of assigning CT numbers or Hounsfield units to each pixel in a reconstructed image?

    <p>To display the linear attenuation coefficients of the tissues</p> Signup and view all the answers

    What is the primary reason water is used as a reference material in CT scans?

    <p>Because of its uniform density and abundance in the body</p> Signup and view all the answers

    What is the unit of measurement assigned to each pixel in a CT scan?

    <p>Hounsfield Unit (H.U.)</p> Signup and view all the answers

    What is the linear attenuation coefficient of dense bone?

    <p>0.46</p> Signup and view all the answers

    Which of the following tissues has a linear attenuation coefficient closest to water?

    <p>White matter</p> Signup and view all the answers

    What is the significance of a CT value of zero?

    <p>It is assigned to water as a reference material</p> Signup and view all the answers

    What happens to CT numbers when tissue density increases?

    <p>They become positive</p> Signup and view all the answers

    Why do different references yield slightly varying linear attenuation coefficients?

    <p>Due to differences in calculation methods</p> Signup and view all the answers

    What is the value of air on the scale where water has a value of 0?

    <p>-1000</p> Signup and view all the answers

    What is the purpose of the scaling factor (K) in CT scans?

    <p>To establish a relative basis for CT numbers</p> Signup and view all the answers

    What is the unit of measurement for CT numbers?

    <p>HU (Hounsfield Units)</p> Signup and view all the answers

    What is the CT number for water?

    <p>0</p> Signup and view all the answers

    What is the formula to calculate the CT number?

    <p>CT Number = (μtissue - μwater) / μwater</p> Signup and view all the answers

    What is the range of CT numbers for soft tissue?

    <p>10-30</p> Signup and view all the answers

    What is the attenuation coefficient of water?

    <p>0.19</p> Signup and view all the answers

    What is the final step in the CT process?

    <p>Image display, storage, and documentation</p> Signup and view all the answers

    What is the purpose of converting the digital CT image to a grayscale image?

    <p>To facilitate interpretation by the radiologist</p> Signup and view all the answers

    What type of display device is usually used to display the CT image?

    <p>LCD (Liquid Crystal Display) monitor</p> Signup and view all the answers

    What is the disadvantage of CRT monitors compared to LCD monitors?

    <p>They are heavier, larger, hotter, and less durable</p> Signup and view all the answers

    What is the arrangement of numerical values called in a digital CT image?

    <p>Matrix</p> Signup and view all the answers

    What represents a volume of patient data or slice thickness in a CT image?

    <p>Voxel</p> Signup and view all the answers

    What is the result of assigning a level of gray to each pixel in a CT image?

    <p>The image becomes grayscale</p> Signup and view all the answers

    What corresponds to the CT number or Hounsfield units for each pixel in a CT image?

    <p>Level of gray</p> Signup and view all the answers

    What is the purpose of displaying the CT image on a television monitor?

    <p>To interpret the image by the radiologist</p> Signup and view all the answers

    Study Notes

    CT Images Display

    • Each pixel in a reconstructed image is assigned a number related to the linear attenuation coefficients (μ) of tissues.
    • These numbers are called CT numbers or Hounsfield units, named after the inventor of CT technology, Sir Godfrey Hounsfield.

    Linear Attenuation Coefficients

    • Linear attenuation coefficients (μ) for some tissues of the body:
      • Air: 0.0003 cm⁻¹
      • Fat: 0.162 cm⁻¹
      • Water: 0.180 cm⁻¹
      • White matter: 0.187 cm⁻¹
      • Blood: 0.182 cm⁻¹
      • Dense bone: 0.46 cm⁻¹

    Hounsfield Units (HU)

    • Water is used as a reference material and assigned a CT value of zero.
    • Tissue materials with density (or attenuation) greater than water have +ve CT numbers.
    • Those less dense than water have –ve CT numbers.
    • A Hounsfield unit (HU) is a digital value assigned to each pixel, lying on a scale where:
      • Water has a value of 0 HU
      • Air has a value of –1000 HU
      • Bone has a value of +1000 HU

    CT Number Calculation

    • CT number is calculated as: CT number = [(μtissue – μwater) / μwater] × K, where K is a constant factor.
    • Value of K determines a contrast factor (scaling factor).

    CT Numbers for Common Tissues

    • CT numbers for common tissues:
      • Air: 1000 – HU
      • Lungs: –300 to 900 HU
      • Fat: –80 to 120 HU
      • Water: 0 HU
      • Muscle: 10 to 30 HU
      • Soft tissue: 50 to 100 HU

    Image Display

    • The final step in the CT process involves image display, storage, and documentation.
    • The CT image is displayed on a television monitor, which is an essential component of the control or viewing console.

    Displaying the Image

    • The display device is usually an LCD (liquid crystal display), each pixel within the image is assigned a level of gray.
    • The gray level assigned to each pixel corresponds to the CT number or Hounsfield units for that pixel.

    Display Monitors

    • CRT (cathode-ray tube) monitors are heavier, larger, hotter, and less durable than the newer LCD monitors.
    • LCD monitors produce higher luminance and high spatial resolution.

    CT Image Matrix

    • The digital CT image is displayed on an arrangement of numerical values called a matrix.
    • The matrix is made up of a series of picture elements, arranged in rows and columns, called pixels.
    • A voxel (volume element) represents a volume of patient data or slice thickness, giving the pixel and added dimension.

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    Related Documents

    W2 CT PHYSICAL PRINCIPLES II.pptx

    Description

    This quiz covers the basics of CT imaging, including CT image display, Hounsfield units, and attenuation coefficients and CT numbers for common tissues.

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