Chapter 7 Flashcards
_______ programs in computed tomography (CT) are essential to ensure optimal image quality while minimizing radiation exposure.
Quality assurance
These programs systematically monitor system performance to identify malfunctions and maintain compliance with established guidelines.
QA
Both ____ and ____ share responsibility for conducting and documenting
QA test
CT technologists, medical physicists
Purpose:Evaluate the system’s ability to distinguish small, closely spaced structures
Frequency: ____
Spatial Resolution
Monthly
Purpose: to assess the system’s ability to differentiate objects with minimal
density differences.
Frequency: ____
Contrast Resolution
Monthly
Purpose: Verify the accuracy of the selected slice thickness
Frequency: _____
SLICE THICKNESS ACCURACY
Semi-annually
Purpose: Ensure proper alignment of laser lights for patient positioning.
Frequency: ____
LASER LIGHT ACCURACY
Semiannually
Purpose: Evaluate the consistency of CT number measurements across the image.
Frequency:
NOISE AND UNIFORMITY
Weekly
Purpose: Ensure the accuracy of CT numbers relative to known linear
attenuation coefficients.
Frequency: _____
LINEARITY
Semiannually
Dose measurements are performed by a ____
Medical Physicist
– are defined as anything appearing on the image that is not present in
the object scanned.
Artifacts
- lower energy photons are absorbed as the x-ray beam passes through an
object, creating a “harder” beam.
Beam Hardening
the periphery of the image appears lighter
Cupping Artifacts
- occurs between dense objects (e.g. Petrous bone
Dark bands or streaks
Occurs when more than one tissue type is contained within a voxel.
PARTIAL VOLUME ARTIFACT
Shading artifacts, when dense objects lies at the edge of the FOV
PARTIAL VOLUME ARTIFACT
inadequate sampling during data acquisition (undersampling)
ALIASING
Fine stripes radiating from dense structures
aliasing
Occurs when irregularly shaped objects with varying densities are present.
EDGE GRADIENT EFFECT
streaking or shading artifact (light and dark areas)
EDGE GRADIENT EFFECT
Cause: metal objects in the SFOV with high attenuation values.
Appearance: Streak artifacts radiating from metal objects.
METALLIC ARTIFACTS
Cause: anatomy extending outside the SFOV, which attenuates and hardens the x-ray beam but is not included in image reconstruction.
Appearance: streak and shading
OUT OF FIELD ARTIFACT
Cause: Faulty or miscalibrated detector elements. (Third gen)
Appearance: Concentric rings centered on the rotational axis.
RING ARTIFACTS
Cause: Electrical surge (short circuit) within the x-ray tube due to residual gas molecules or degraded vacuum.
Appearance: Variable streaks ranging from mild to severe.
TUBE ARCHING ARTIFACT
Cause: artifacts due to interpolation and reconstruction in helical scanning and wider detector arrays.
Appearance: subtle inaccuracies in CT numbers, windmill artifacts (streaks and
shading in dense structures)
HELICAL AND CONE BEAM EFFECT
