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CT Review 7
Artifacts
Question | Answer |
---|---|
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 |