CT Artifacts in Medical Imaging
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Questions and Answers

What is the primary factor that causes streaks to appear in CT images?

  • High contrast objects within the scanning area
  • Metal implants within the scan range
  • Improper selection of reconstruction filters
  • Inconsistent data acquisition during the scan (correct)

    • Which of the following artifact types is characterized by layering effects that appear superimposed on the original image?

  • Bands (correct)
  • Shading
  • Rings
  • Streaks

    • What is the primary cause of beam hardening artifacts in CT?

  • The use of metal implants in the scan area
  • The interaction of x-rays with dense objects (correct)
  • Improper alignment of the CT gantry
  • Excessive patient movement during the scan

    • What is the effect of shading artifacts on CT images?

    <p>The distortion of CT numbers in tissues near high contrast objects (A)</p> Signup and view all the answers

    Which of the following is NOT a type of patient-induced CT artifact?

    <p>Ring artifact (C)</p> Signup and view all the answers

    What is the primary cause of edge gradient artifacts in CT images?

    <p>Patient motion (D)</p> Signup and view all the answers

    Which of the following is NOT a solution to minimize beam hardening artifacts in CT?

    <p>Reducing noise level (A)</p> Signup and view all the answers

    How are metal artifacts best reduced?

    <p>Removing metallic objects from the scan field (C)</p> Signup and view all the answers

    Which of these describes beam hardening artifacts?

    <p>Dark bands between dense objects (B)</p> Signup and view all the answers

    What is one of the effects of partial volume artifacts?

    <p>Shading in certain views (D)</p> Signup and view all the answers

    What can help reduce edge gradient artifacts?

    <p>Opting for low HU oral contrast (B)</p> Signup and view all the answers

    Which solution is effective for addressing photon starvation artifacts?

    <p>Increasing kVp (C)</p> Signup and view all the answers

    What causes aliasing artifacts during imaging?

    <p>Insufficient data resulting from undersampling (D)</p> Signup and view all the answers

    What is a common result of tube arcing in imaging equipment?

    <p>Crackling sound (B)</p> Signup and view all the answers

    What is a solution for addressing artifacts caused by equipment malfunction?

    <p>Detector replacement (B)</p> Signup and view all the answers

    How can the partial volume effect be minimized during imaging?

    <p>By selecting thinner slice increment (D)</p> Signup and view all the answers

    What typically results from incorrect calibration of a detector in a CT scanner?

    <p>Ring artifacts (B)</p> Signup and view all the answers

    Flashcards

    Edge gradient artifact

    An artifact caused by abrupt changes in density at object edges in CT imaging.

    Motion artifacts

    Artifacts from patient motion that appear as shading, streaking, blurring, or ghosting in the images.

    Beam-hardening artifacts

    Artifacts caused by lower-energy photons being absorbed in dense materials, resulting in dark bands or streaks.

    Metal artifact

    Artifacts resulting from metal objects causing 'star streaking' due to photon absorption, creating incomplete profiles.

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    Out of field artifact

    Artifacts caused when parts of the patient are outside the scanning field of view, blocking detectors and affecting image quality.

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    Artifact in CT

    Any non-present item appearing on a CT image, causing discrepancies.

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    Types of CT Artifacts

    Artifacts are classified into patient-based, equipment-induced, and physics-based causes.

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    Streak Artifacts

    Intense straight lines on the CT image caused by inconsistencies in data acquisition.

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    Beam Hardening

    A type of artifact where low-energy rays are absorbed more, creating dark bands.

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    Partial Volume Effect

    Artifact caused when more than one type of tissue is included in a pixel, leading to shading in images.

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    Aliasing

    Artifact due to insufficient data leading to undersampling, resulting in sharp edges or lines in images.

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    Photon Starvation: Noise

    Horizontal streak artifacts occur when there are insufficient photons reaching the detector, often at highly attenuating areas.

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    Ring Artifact

    Artifact caused by a malfunctioning detector in a scanner, leading to loss of data in that detector row.

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    Tube Arcing

    A short circuit effect where tungsten vapor affects the electrons aimed at the target during imaging.

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    Solutions for Artifacts

    Various methods to mitigate artifacts include thinner slices, increased scan time, and adjusting detector settings.

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    Study Notes

    Artifacts in CT

    • Artifacts are anything appearing on a CT image that isn't present in the actual object being scanned.
    • They represent a discrepancy between the CT numbers in the image and the expected CT numbers based on the linear attenuation coefficient.
    • Artifacts have diverse presentations and causes.
    • Sources of artifacts can be broadly categorized as patient-based, equipment-based and physics-based (e.g., radiation).

    Learning Outcomes

    • Students should be able to define artifacts in CT.
    • Students should be able to identify different types of CT artifacts.
    • Students should be able to determine appropriate steps to reduce artifacts in CT images.

    Appearance of Artifacts

    • Streaks: Intense straight lines, either light or dark, enhanced by the reconstruction filter. They stem from inconsistencies in data collection, such as metal or patient movement during scans. They can make images unreadable or unreliable due to false image production during reconstruction.
    • Shading: Appear near high contrast objects (e.g., dense objects) within a softer tissue region. This artifact occurs because the CT number in the image shifts, potentially leading to misdiagnosis.
    • Bands: Display a layered effect, superimposed on the original images.
    • Rings: Circular formations on images, superimposed. These are caused by faulty or miscalibrated detectors.

    Patient-Induced Artifacts

    • Motion: Results in shading, streaking, blurring, or ghosting artifacts. Voluntary or involuntary motions during the scan cause these artifacts.
    • Beam Hardening: Caused by the polychromatic nature of the x-ray beam used in CT. Lower-energy photons are preferentially absorbed, creating a "harder" beam as it passes through objects.
    • Metal Artifacts: Create "star streaking" artifacts. Metal objects in the field of view (FOV) absorb photons, causing incomplete profiles and streaking. Removing the objects is the primary solution.
    • Out of Field Artifacts: Arises when the patient is not adequately enclosed in the scanning field of view (FOV). Body parts outside the FOV can obstruct detectors and further harden the x-ray beam, causing streaking and shading artifacts.
    • Edge Gradient Artifacts: These artifacts are generated when objects with substantial density differences (e.g., barium and air) are adjacent. They are highly visible as streaks, but can be reduced using thinner slices and using a low HU-oral contrast instead of barium/water.

    Equipment Artifacts

    • Partial Volume Effect: Occurs when an off-center dense object partially protrudes into the x-ray beam path. This appears as shading in some image views. Thinner slice selection and incrementations minimize partial volume artifacts.
    • Aliasing: Insufficient data collection due to undersampling (e.g. wrong helical pitch), results in inaccuracies, causing sharp edges and lines to appear incorrectly in the imaging. Increasing scan time, reducing pitch, slowing gantry rotation and use of complete arc scans reduces the risk.
    • Photon Starvation (Noise): Occurs in areas with high attenuation (e.g., shoulder). Insufficient photons reach the detectors in these regions, resulting in horizontal streaks. Using higher kVp and mAs and thicker slices helps reduce the risk.
    • Ring Artifacts: Caused by malfunctions in the detectors, leading to loss of data in a specific area. Recalibrating the detector or replacing it is typically needed.
    • Tube Arcing: Created by tungsten vapor in the x-ray tube impacting the projectile electrons intended for collisions with the target. This causes crackling sounds and potentially produces high-voltage arcing in the tube. Replacing the damaged tube.
    • Line in Topogram Artifacts: Continuous lines result from faulty detectors. Replacement of the detector provides resolution.
    • Staircase Artifacts: Stem from improper selection of slice thickness and increments. Selecting thinner slices will reduce the staircase effect.

    Solutions for Artifacts

    • Explain the procedure and communicate effectively with the patient to avoid voluntary motions, use shorter scan times for involuntary motions.
    • Use proper filtration or calibration correction software to address beam hardening artifacts.
    • Remove external metal objects. Use specific software. Adjust gantry angle.
    • Enclose the whole patient into FOV to address out of field artifacts. Use larger FOV, taping technique and patients position adjustments.
    • Utilize thinner slices to reduce edge gradient artifacts, use lower HU contrast.
    • Using thinner and appropriate slice selections prevents the partial volume effect.
    • Increase scan time, reduce pitch, and/or slow gantry rotation to mitigate aliasing.
    • Increase kVp or mAs, increase slice thickness to reduce photon starvation artifacts.
    • Calibrate or replace the faulty detector to remedy ring artifacts.
    • Replace the defective x-ray tube to resolve tube arcing.
    • Replace faulty detectors to fix line (in topogram) artifacts and staircase artifacts.

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    Related Documents

    CT Image Artifact PDF

    Description

    Test your knowledge on the factors causing streaks and other artifacts in CT images. This quiz covers different artifact types like beam hardening and patient-induced effects. Enhance your understanding of how these artifacts impact image quality.

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