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21 Cards in this Set
- Front
- Back
_______________ is the increase in average energy of the x-ray beam as it penetrates tissue.
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beam hardening
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The degree of beam hardening is dependent upon the _______________ and _______________.
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body part being penetrated
its composition |
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beam hardening can cause a variation in the _______________ of a given tissue type from the periphery to the center of an image.
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CT Number
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______________ is a phenomenon when central tissues are surrounded by denser material and as a result of beam hardening may appear to be less dense than they actually are.
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cupping
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Beam hardening may be manifested by broad streaks when scanning thick body parts. Anatomical parts that may cause this are:(4)
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petrous pyramids of the temporal bones
shoulders ribs hips |
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What can be done to minimize beam hardening?(4)
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Use thin slices
dilute the contrast perform scan with slight delay after iv contrast scan in the opposite direction |
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What is partial volume artifact?
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partial volume artifact is a situation where a voxel contains more than one type of tissue. The CT number assigned to this voxel is determined by a weighted average of the densities within the voxel rather than displaying each tissue type individually.
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To minimize partial volume artifacts, ____________ should be selected.
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thinner slices
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As slice thickness decreases, apparent noise in the image is ______________. to counteract this, the mAs should be _______________.
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increased
increased |
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A ghost artifact looks like a _________________ of a tissue boundary.
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double margin
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It is important to ensure your patient is _______________, _______________, and _______________.
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comfortable
understands the procedure able to perform necessary breathing requirements |
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Metal artifacts can cause streaks emanating from the object. These are caused by a combination of: (4)
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beam hardening
edge gradient effect partial volume effect motion |
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_______________ occurs when different attenuation coefficients are obtained for the same object depending upon the vantage point of the projection.
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edge gradient effect
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The edge gradient effect appears as streaks which emanate from structures that have _______________ and _______________.
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sharp edges
great density differences from neighboring tissues |
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The _______________ the detector, and the _______________ projections acquired reduce the chances of edge gradient effects occurring.
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smaller
more |
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A way that the CT tech can reduce edge gradient effect from occurring is:(3)
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if possible, move the structure that causes the edge gradient effect or reposition patient
Increase data sampling, or oversampling use thinner slices |
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________________ occur because the anatomy outside the scan field-of-view contributes toward the attenuation and hardening of the x-ray beam, but it is ignored during the image reconstruction process.
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out-of-field artifacts
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Sometimes out-of-field artifacts may be caused by _______________
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an obstruction of the reference detectors by the patient's body
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The result of out-of-field artifacts is a variation and inaccuracy of the _______________ of the tissues in the final images.
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CT Number
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The Ring Artifact is typically caused by a _______________ on a 3rd generation scanner.
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faulty detector
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If a detector has an offset difference of as little as _______________ with neighboring detectors, a ring artifact may result.
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0.1%
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