Image Artifact (CTBC 9) Flashcards
Artifact is any _______ & may lead to _______.
Any distortion/error that doesn’t accurately represent area being imaged
May lead to misdiagnosis, loss of image info
Sources of Artifact (3)
Incorrect Protocol Selection
Improper Positioning
Equipment Failure
2 Broad categories of Artifacts
Patient Artifacts
Equipment Artifacts
Streak Artifact
Abnormal streaking on image
Patient Artifacts (are caused by) (2)
Something in Patient
Something in scan field (e.g., EKG lines)
Equipment Artifacts (are caused by) _______E.g., (2)
Things outside scan field. E.g., broken detector, processing failure
Beam Hardness
Average energy of photons in beam
Beam hardness _______ as it passes through any material because the _______ energy photons are _______ first
Increases
Lower Energy
Attenuated First
Beam Hardening Artifact appears as _______ and is especially common when _______
Dark or Light streaks radiating from dense object(s) in image
Especially common when dense objects adjacent to low-density materials
Beam hardening is common in basilar fossa (of skull) when passing through _______ portions
Petrous portions
Beam hardening common in pelvis between _______.
Femurs
When arms are left down to the sides, resultant streaking is called
Beam Hardening
Beam Hardening can generally be minimized with (2)
Special Software and Filters
Most intense form of beam hardening
Metal Artifact
Edge Gradient Artifact (2)
Mild form of beam hardening from areas of high contrast (e.g., ,bone-brain interface, fluid level b/w contrast & bowel gas)
Appears as streaks extending from area of high contrast
Motion Artifact occurs when
From voluntary (swallowing/breathing) or involuntary (cardiac/bowel peristalsis) motion
Motion Artifact typically appears as (2)
Blurring of Image
Streaks extending from areas of high density (e.g., bone)
Misregistration
Misalignment of anatomy
(E.g., breathing during chest CT will cause same ribs to appear at different locations in the scan)
Out-of-Field Artifact
White streaking artifact on the periphery of the patient occurring when the scanner assumes the (very-dense) edges of a patient are within the SFOV
Partial Volume Averaging
Misrepresentation of anatomy d/t averaging of tissues into given slice which can morph or hide pathology–or cause normal anatomy to appear pathologic
Artifact d/t failure of element within detector array appears as
Ring Artifact
Can also result from contrast on mylar window or on detector itself
Often corrected by running air cal
Aliasing Artifact
Appears as series of evenly spaced streaks extending from object edges
Result of under-sampling/missing info
E.g., from fast rotation time or fast pitch that results in fewer projections
Fan beam
Scan using only a few detector rows
Cone beam
Scan using several detector rows
Cone beam artifact
Distortion in shape of imaged objects resulting from use of wider beam using more detector rows
(unlikely in modern scanners)
Artifact presenting as a pattern of parallel streaks across the entire image (usually affecting one axial slice)
Tube arcing
This occurs when the x-ray tube shorts d/t electron stream leaping from cathode to tube envelope (instead of to anode) & there is temporary loss of x-ray output
Tube arcing (electrons form an arc away from intended path)
Artifact often corrected by running air cal
Ring Artifact
Can result from contrast on mylar window or on detector itself
Ring Artifact
