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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.
beam hardening
The degree of beam hardening is dependent upon the _______________ and _______________.
body part being penetrated

its composition
beam hardening can cause a variation in the _______________ of a given tissue type from the periphery to the center of an image.
CT Number
______________ 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.
Beam hardening may be manifested by broad streaks when scanning thick body parts. Anatomical parts that may cause this are:(4)
petrous pyramids of the temporal bones
What can be done to minimize beam hardening?(4)
Use thin slices

dilute the contrast

perform scan with slight delay after iv contrast

scan in the opposite direction
What is partial volume artifact?
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.
To minimize partial volume artifacts, ____________ should be selected.
thinner slices
As slice thickness decreases, apparent noise in the image is ______________. to counteract this, the mAs should be _______________.

A ghost artifact looks like a _________________ of a tissue boundary.
double margin
It is important to ensure your patient is _______________, _______________, and _______________.

understands the procedure

able to perform necessary breathing requirements
Metal artifacts can cause streaks emanating from the object. These are caused by a combination of: (4)
beam hardening

edge gradient effect

partial volume effect

_______________ occurs when different attenuation coefficients are obtained for the same object depending upon the vantage point of the projection.
edge gradient effect
The edge gradient effect appears as streaks which emanate from structures that have _______________ and _______________.
sharp edges

great density differences from neighboring tissues
The _______________ the detector, and the _______________ projections acquired reduce the chances of edge gradient effects occurring.

A way that the CT tech can reduce edge gradient effect from occurring is:(3)
if possible, move the structure that causes the edge gradient effect or reposition patient

Increase data sampling, or oversampling

use thinner slices
________________ 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.
out-of-field artifacts
Sometimes out-of-field artifacts may be caused by _______________
an obstruction of the reference detectors by the patient's body
The result of out-of-field artifacts is a variation and inaccuracy of the _______________ of the tissues in the final images.
CT Number
The Ring Artifact is typically caused by a _______________ on a 3rd generation scanner.
faulty detector
If a detector has an offset difference of as little as _______________ with neighboring detectors, a ring artifact may result.