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Artifacts in MedicalImaging

Projection Radiography (x-ray)

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CT – beam hardening

CT - streaking

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CT - motion

CT – out of field

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MRI – chemical shift

The chemical shift artifact is commonly noticed in the spine at thevertebral body end plates, in the abdomen, and in the orbits where fatand other tissues form borders. In the frequency direction, the MRIscanner uses the frequency of the signal to indicate spatial position.Since water in organs and muscle resonate at a different frequency thanfat, the MRI scanner mistakes the frequency difference as a spatial(positional) difference.

MRI - susceptibility

Susceptibility artifacts occur as the result of microscopic gradientsor variations in the magnetic field strength that occurs near theinterfaces of substance of different magnetic susceptibility.

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MRI - aliasing

Aliasing or wrap-around is a common artifact that occurs when the fieldof view (FOV) is smaller than the body part being imaged. The part of thebody that lies beyond the edge of the FOV is projected on to the otherside of the image.

MRI - ringing

Gibbs or truncation artifacts are bright or dark lines that are seen paralleland adjacent to borders of abrupt intensity change, as when going frombright CSF to dark spinal cord on a T2-weighted image.

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MRI - zipper

There are various causes for zipper artifacts in images. Most of them arerelated to hardware or software problems beyond the radiologist’simmediate control.

MRI - motion

Phase-encoded motion artifacts (ghosting) appear as bright noise orrepeating densities oriented in the phase direction, occurring as the resultsof motion during acquisition of a sequence.

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MRI - overflow

RF overflow artifacts cause a nonuniform, washed-out appearance to an image as shown inthe following axial image of a head. This artifact occurs when the signal received by thescanner from the patient is too intense to be accurately digitized by the analog-to-digitalconverter

Ultrasound - shadowing

Shadowing: Caused by sound striking a strong reflective interfaceExample: areas behind ribs or gall stones

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Ultrasound - shadowing

Ultrasound - reverberation

Reverberation: Caused by sound interfacing with two structures ofmarkedly differing acoustic properties;example: inadequate amount of gel, obstructing bowel gas

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Ultrasound - enhancement

Enhancement: Caused by sound travelling throughfluid-filled structures without attenuation (example:area behind cysts, area behind gallbladder)

Ultrasound - processing

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Ultrasound - processing

Ultrasound

No ghosting artifacts in ultrasound…