CT Image Quality
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Questions and Answers

What is the effect of increasing the field of view on spatial resolution?

  • It does not affect spatial resolution
  • It decreases spatial resolution (correct)
  • It has no significant effect on image quality
  • It increases spatial resolution

    • What is the relationship between pixel size and spatial resolution?

  • Larger pixel size results in higher spatial resolution
  • Smaller pixel size results in lower spatial resolution
  • Smaller pixel size results in higher spatial resolution (correct)
  • Pixel size has no effect on spatial resolution

    • What is the effect of increasing magnification on spatial resolution?

  • It does not affect spatial resolution
  • It enhances image contrast
  • It increases spatial resolution
  • It decreases spatial resolution (correct)

    • What is the effect of increasing pitch on spatial resolution?

    <p>It decreases spatial resolution</p> Signup and view all the answers

    What is the effect of increasing slice thickness on spatial resolution?

    <p>It decreases spatial resolution</p> Signup and view all the answers

    What is contrast resolution dependent on?

    <p>Ability to differentiate structures with slight density variations</p> Signup and view all the answers

    What is the limitation of screen-film radiography in terms of contrast resolution?

    <p>Objects must have at least a 5-10% difference in contrast</p> Signup and view all the answers

    What is temporal resolution controlled by?

    <p>Gantry rotation speed and detector channels</p> Signup and view all the answers

    What is the importance of high temporal resolution in CT imaging?

    <p>It is important for imaging moving structures and dynamic flow studies</p> Signup and view all the answers

    What is the purpose of the ACR CT accreditation phantom?

    <p>To examine a broad range of scanner parameters</p> Signup and view all the answers

    What is the primary factor that determines the usefulness of a CT image?

    <p>Image quality</p> Signup and view all the answers

    What is the unit of measurement for spatial frequency in CT scanners?

    <p>Line pairs per centimeter (lp/cm)</p> Signup and view all the answers

    Which method is used to graphically represent a system's performance in terms of spatial resolution?

    <p>Modulation transfer function (MTF)</p> Signup and view all the answers

    What is the ability to distinguish between object or structures that differ in density?

    <p>Spatial resolution</p> Signup and view all the answers

    What is the purpose of measuring spatial resolution in CT imaging?

    <p>To provide an accurate diagnosis</p> Signup and view all the answers

    What is the relationship between spatial resolution and line pair phantom?

    <p>Spatial resolution is directly measured using a line pair phantom</p> Signup and view all the answers

    What is the primary factor that affects the ability of a CT scanner to distinguish between object or structures that differ in density?

    <p>Spatial resolution</p> Signup and view all the answers

    What is the term used to describe the number of line pairs per unit length?

    <p>Spatial frequency</p> Signup and view all the answers

    Which of the following is a measure of CT image quality?

    <p>All of the above</p> Signup and view all the answers

    What is the purpose of measuring CT image quality?

    <p>To provide an accurate diagnosis</p> Signup and view all the answers

    What is the purpose of the phantom in the Slice Thickness QA?

    <p>To include ramp or step-wedge of known measurements</p> Signup and view all the answers

    How often is the Noise and Uniformity QA performed?

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

    What is the acceptable range of CT numbers for air in the CT Number QA?

    <p>-1000 ± 5</p> Signup and view all the answers

    What is the purpose of the phantom in the Contrast Resolution QA?

    <p>To contain objects of variable sizes with a small difference in density from their surroundings</p> Signup and view all the answers

    How often is the LinearITY QA performed?

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

    What is the purpose of the ROI in the Noise and Uniformity QA?

    <p>To obtain the standard deviation of the CT numbers</p> Signup and view all the answers

    What is the purpose of the phantom in the CT Number QA?

    <p>To test the average CT number of water and air</p> Signup and view all the answers

    How often is the Slice Thickness and Laser Light Accuracy QA performed?

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

    What is the acceptable range of CT numbers for water in the CT Number QA?

    <p>0 ± 3</p> Signup and view all the answers

    What is the purpose of the phantom in the Linearity QA?

    <p>To contain a variety of objects with known densities</p> Signup and view all the answers

    Study Notes

    CT Image Quality

    • CT image quality is directly related to its usefulness in providing an accurate diagnosis.

    Spatial Resolution

    • Spatial resolution is the ability to distinguish between objects or structures that differ in density.
    • Measured using two methods: directly using a line pairs phantom, or by data analysis known as modulation transfer function (MTF).
    • Factors affecting spatial resolution:
      • Field of view: increases in FOV decrease spatial resolution.
      • Pixel size: smaller pixel size increases spatial resolution.
      • Magnification: increasing magnification decreases spatial resolution.
      • Pitch: higher pitch decreases spatial resolution.
      • Slice thickness: larger slice thickness decreases spatial resolution.

    Contrast Resolution

    • Contrast resolution is the ability to differentiate a structure that varies only slightly in density from its surroundings.
    • CT is superior to all other clinical modalities in its contrast resolution.
    • Objects with a 0.25-0.5% contrast variation can be distinguished on CT images.

    Temporal Resolution

    • Temporal resolution refers to a system's ability to rapidly acquire data.
    • Controlled by: gantry rotation speed, number of detector channels in the system.
    • High temporal resolution is important when imaging moving structures (e.g., heart) and for studies dependent on dynamic flow (e.g., CT angiography).

    Quality Assurance

    • ACR CT accreditation phantom consists of four modules that can be used to examine a broad range of scanner parameters.
    • QA tests include:
      • Contrast resolution QA: assesses low-contrast resolution using a phantom with objects of variable sizes with a small difference in density.
      • Slice thickness and laser light accuracy QA: measures slice thickness using a phantom with known measurements and evaluates laser light from the gantry.
      • CT number QA: tests the average CT number of water (should be 0 ± 3) and air (-1000 ± 5).
      • Noise and uniformity QA: measures noise using the standard deviation of CT numbers within a single ROI and uniformity by placing several ROIs within the phantom.
      • Linearity QA: measures linearity using a phantom containing a variety of objects with known densities.

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    Related Documents

    CT Image Quality PDF

    Description

    Assess your understanding of CT image quality, including spatial resolution, contrast resolution, temporal resolution, CT number accuracy, and quality assurance.

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