Week 5 Flashcards
(26 cards)
Ability to differentiate small, nearby objects of similar density
Spatial resolution
The lack of sharpness that occurs when a true point in the object being scanned is not represented as a true point on the image is called:
Point spread function
Describes the unsharpness when a linear source is not represented as a clear line on the image
Line spread function
The CT system’s ability to differentiate between similar tissues is called:
Contrast resolution
Image noise can be reduced by:
Increasing slice thickness
The ability of the CT scanner to image moving objects effectively is called:
temporal resolution
Correct assignment of HU values
Linearity
The ability of the CT scanner to consistently assign the correct HU numbers
Uniformity
The path pf the x-ray beam from the tube to the detectors
Beam geometry
All of the following result from an increase in kVp, EXCEPT
-reduced absorption
-higher average beam energy
-increased scatter
-increased image contrast
increased image contrast
Broad, dark streaks between or along dense objects; type of beam hardening artifact
Streaking artifact
Occurs when similar tissues within a voxel are averaged as one Hounsfield unit
Partial volume averaging artifact
Occurs when impurities in the x-ray tube cause a short circuit
Tube arcing
Artifact caused by faulty detectors and faulty digital acquisition systems
Ring artifacts
Appear as shadowing on the image; corrected by using interpolation
low-frequency artifacts
Caused by abrupt longitudinal changes of the body; corrected using algorithms
high-frequency artifacts
Artifacts appearing as streaks that originate from body structures with tissues that vary significantly in density, such as bone and soft tissue interfaces, are called:
Edge gradient artifacts
Occurs when peripheral anatomy interferes with the signal
out-of-field artifacts
Which tests the performance of a computed tomography (CT) scanner on a number of parameters and compares the performance with a standard?
Quality control
Which of the following is not an essential step in a QC program?
a. Phantom construction
b. Routine performance evaluation
c. Error correction
d. Acceptance testing
A
The average CT number of water QC test should be done:
Daily
T/F: Often a QC program can result in reduced downtime.
True
What is the most upfront way to reduce or eliminate the motion of an object?
Increase scan speed
What is defined as the smallest object that can be visualized at a given contrast level and dose?
Low-contrast performance
