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CT Review 7

Artifacts

QuestionAnswer
What is the definition of an artifact? Any discrepancy between hounsfield numbers and reconstructed image and true attenuation coefficients of the object.
Describe the cupping artifact? dark bands or streaks between dense objects in the image
What techniques can be used to reduce beam hardening artifacts? algorithms, reduce slice thickness, beam shaping filtration (bow tie filter)
Partial volume artifact can manifest itself in different ways. What are some of those ways? blurriness, ballooning out, bans/streaks
To minimize partial volume artifacts you may reduce slice thickness but it may/will increase what two things? noise and dose
What is aliasing artifact? pin wheel artifact
What are the two types of aliasing artifacts? view aliasing and ray aliasing
Metallic artifacts are seen as how on the image? star effect, streaks
List 3 metallic materials that will cause artifacts. prosthetics, electrodes, jewelry
There are two types of motion artifacts, what are they? voluntary and involuntary
What are the two techniques used to minimize out of field artifacts? proper position of the patient and correct SFOV
What generation ct scanner can you start to see ring artifacts? 3rd gen
Sharply defined thin rings in an image are usually caused by what? detector channel failure
The spreading of the xray beam along the z-direction is responsible for the artifact called? Cone beam
Stair step artifacts appear around the edges of structures is what? MPR and 3D
What kind of artifact causes faint line to be visible in MPR and 3D reformatted images from helical scanning because the helical interpolation process gives rise to non-homogeneous noise along the z-axis? zebra
What are the different types of artifacts? user related, system, voluntary and involuntary
Artifacts may be caused by "thick" body parts such as? temporal bone, shoulders, ribs, and dense oral or intravenous contrast
The beam is less hardened by fat and more by what? bone
What is used to harden edges of the beam when it goes thru thinner parts of the body? bow tie filter
Quantum noise causes what type of artifacts? 1.black and white (salt and pepper) 2.horizontal streaks
What is the partial volume effect? an error that occurs when a structure is only partly positioned within a voxel and the attenuation for the object is not accurately represented by a pixel value.
What is an Out of Field artifact? hyperdense streaking that occurs when a portion of the patient has been positioned outside the SFOV
What is an edge gradient artifact? streak artifact that occurs at the interface between a high density object and the lower attenuation material surrounding it
What is beam hardening? when low energy photons are absorbed as the xray beam passes thru an object, resulting in an increase in the average photon energy of the beam
what is misregistration? artifact that occurs when pt motion between consecutive acquisitions causes misalignment of data and the potential loss of anatomic information
Created by: Chrslarsen