Medical Imaging Artifacts Overview
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Questions and Answers

What is one corrective measure to reduce shading artifacts caused by improper coil loading?

  • Load the coil correctly (correct)
  • Use higher frequency RF pulses
  • Increase the flip angle of RF pulses
  • Adjust the slice selection gradient

    • Which of the following is a consequence of cross excitation during an RF pulse?

  • Improved image resolution of the T2-weighted image
  • Increased signal intensity in the excited slice
  • Enhanced longitudinal magnetization in adjacent slices
  • Reduced signal intensity in adjacent slices (correct)

    • What is a primary cause of shading artifacts in MRI?

  • High temperature of the MRI machine
  • Long exposure time to RF pulses
  • Excessive fluid in the imaging region
  • Uneven excitation of nuclei due to RF pulses (correct)

    • What can be done to address inhomogeneity of the magnetic field?

    <p>Perform shimming adjustments</p> Signup and view all the answers

    What contributes to the improper loading of the coil when observing shading artifacts?

    <p>Connection issues in the anterior part of the coil</p> Signup and view all the answers

    What primarily causes Ghosts/Motion Artifacts during imaging?

    <p>Body parts moving along a gradient</p> Signup and view all the answers

    Which of the following is NOT a corrective measure for Ghosts/Motion Artifacts?

    <p>Increasing the scan speed</p> Signup and view all the answers

    Which type of motion can lead to the smearing of images in Ghosts/Motion Artifacts?

    <p>Nonperiodic movement</p> Signup and view all the answers

    What is the purpose of cardiac gating during imaging?

    <p>To prevent image blurring from heart movement</p> Signup and view all the answers

    What is a potential artifact caused by respiration during the imaging process?

    <p>Respiratory motion artifacts</p> Signup and view all the answers

    Which technique is specifically mentioned for suppressing blood flow motion artifacts?

    <p>Spatial Presaturation (SAT)</p> Signup and view all the answers

    What typically describes the axis along which ghosts appear in Ghosts/Motion Artifacts?

    <p>Phase encoding axis</p> Signup and view all the answers

    What kind of artifact is characterized by it being a replica of something in an image?

    <p>Ghost artifact</p> Signup and view all the answers

    What happens to the signal when a 90-degree RF pulse is sent, but no longitudinal magnetization exists?

    <p>No signal is generated.</p> Signup and view all the answers

    Which artifact occurs when the imaging field of view (FOV) is smaller than the anatomy being imaged?

    <p>Aliasing artifact</p> Signup and view all the answers

    What is the primary cause of chemical shift artifacts between fat and water?

    <p>Difference in precessional frequencies</p> Signup and view all the answers

    Which measure can be employed to correct for aliasing along the phase encoding direction?

    <p>Increase FOV along phase encoding direction</p> Signup and view all the answers

    At which field strength are chemical shift artifacts generally more pronounced?

    <p>Higher field strengths (3.0 Tesla)</p> Signup and view all the answers

    Which of the following is NOT a corrective measure for aliasing artifacts?

    <p>Using gradient coils</p> Signup and view all the answers

    Chemical shift is typically expressed in which unit?

    <p>Parts per million (ppm)</p> Signup and view all the answers

    The region of dark signal void and bright signal at the interface of fat and water is due to what phenomenon?

    <p>Signal misregistration</p> Signup and view all the answers

    What visual characteristic is associated with Gibbs or Truncation artifacts?

    <p>Bright and dark lines at abrupt intensity changes</p> Signup and view all the answers

    What causes Magnetic Susceptibility artifacts?

    <p>Differences in precessional frequency due to tissue magnetization</p> Signup and view all the answers

    Which of the following is a corrective measure for reducing Gibbs artifacts?

    <p>Increasing the matrix</p> Signup and view all the answers

    Zipper artifacts are primarily caused by which factor?

    <p>External RF signals entering the scanning room</p> Signup and view all the answers

    How can one differentiate the effect of Magnetic Susceptibility artifacts?

    <p>By identifying signal loss and distortion at tissue interfaces</p> Signup and view all the answers

    Which artifact is characterized by uneven contrast and loss of signal intensity in parts of an image?

    <p>Shading artifact</p> Signup and view all the answers

    Which measure can help manage zipper artifacts?

    <p>Reporting system-generated artifacts to the service engineer</p> Signup and view all the answers

    What is a common cause of magnetic susceptibility artifacts related to tissue types?

    <p>Magnetization differences between soft tissues and air</p> Signup and view all the answers

    Study Notes

    Artifacts and Their Compensations

    • Artifacts are false features in medical images, arising during the imaging process.
    • Their causes can be rectified when known.

    Outline of Presentation

    • Artifacts include:
      • Ghosts/Motion Artifacts
      • Aliasing/Wraparound
      • Chemical Shift Artifacts
      • Gibbs or Truncation artifacts
      • Magnetic Susceptibility Artifact
      • Zipper Artifacts
      • Shading Artifacts
      • Cross Excitation

    Ghosts/Motion Artifacts

    • Ghosts are replicas of objects within the image.
    • Caused by body parts moving during scanning.
    • Movement during image acquisition can lead to mismapping.
    • Periodic movements (breathing, heartbeats) produce ghosting
    • Nonperiodic movement causes image smearing.
    • Ghosting occurs along phase-encoding axis.
    • Corrective steps:
      • Patient stabilization with straps and cushions
      • Shorter scanning sequences
      • Cardiac gating (mandatory for cardiac motion)
      • Respiratory gating/compensation (for respiratory motion)
      • Spatial Presaturation (SAT) technique to reduce blood flow motion artifacts

    Aliasing/Wraparound

    • Anatomy outside the field of view (FOV) appears within the image.
    • Occurs when FOV is smaller than the anatomy being imaged.
    • Aliasing happens along frequency and phase encoding axes.
    • Corrective steps:
      • Increase field of view (FOV)
      • Filter frequency-encoded direction
      • Increase FOV along phase-encoding direction

    Chemical Shift Artifacts

    • Occur at the interface between water and fat due to different proton precessional frequencies.
    • Expressed in parts per million (ppm).
    • Water protons have a higher frequency than fat.
    • Causes signal voids or misregistration, displaying as a dark region on one side of the tissue and a bright signal on the other side of the water-fat interface.
    • More pronounced in higher field strengths.
    • Corrected by fat suppression techniques.

    Gibbs or Truncation Artifacts

    • Bright and dark lines parallel to intensity change boundaries.
    • Seen in CSF, spinal cord, fat, and muscle.
    • Occur along phase-encoding direction.
    • Corrections include increasing the matrix size and using filters.

    Magnetic Susceptibility Artifacts

    • Magnetic susceptibility: the ability of substances to become magnetized.
    • Different magnetization degrees between tissues can lead to signal dephasing and loss
    • High susceptibility differences, such as between soft tissues and air, produce signal loss and distortion of tissue boundaries in close proximity to air sinuses.
    • Other causes: metal objects.
    • Corrective steps:
      • Using SE sequences
      • Removing metal objects

    Zipper Artifacts

    • Caused by external RF signals interfering with the image.
    • Often related to hardware/software problems or opening the scanner door during scanning.
    • Appears as perpendicular parallel lines to the frequency axis.
    • Corrective measures: reporting system-generated artifacts to engineers

    Shading Artifacts

    • Uneven contrast with signal intensity loss in specific regions of the image.
    • Caused by uneven excitation of nuclei, improper coil loading, or magnetic field inhomogeneity.
    • Corrected by properly loading the coil and shim corrections to reduce inhomogeneity.

    Cross Excitation

    • Adjacent slices can receive RF energy and be excited.
    • The excited nuclei in adjacent slices do not have enough longitudinal magnetization for proper tilting.
    • This reduces signal intensity in the adjacent slices.
    • Remedy: increasing interslice gap.

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    Related Documents

    MRI Artifacts and Compensations PDF

    Description

    This quiz explores various artifacts that can appear in medical imaging and their compensations. Understanding the causes of these artifacts, such as motion and chemical shifts, can help practitioners rectify errors in medical images. Dive into the complexities of ghosting, aliasing, and more.

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