CT Image Quality and Display Flashcards
Primarily controlled by resolution and noise consideration
CT IMAGE QUALITY
Varied with window level and
window width controls
DENSITY AND CONTRAST
CT image: requires __ contrast
difference
4%
Diagnostic image: requires __
contrast difference
10%
Depends on pixel, voxel and matrix size
RESOLUTION
resolves high-contrast
objects 1.5 times its size
Pixel size:
+Voxel size: __mm
8-13mm
seen better in smaller pixel size
+High contrast objects:
seen better in a larger pixel size
Low contrast objects:
+CT: __mm resolving power
+Conventional: __mm resolving power
CT: 0.35mm
Conventional: 0.25mm
+Undershoot and overshoot
+Occurs when two objects have >60% difference in attenuation
coefficients
INTERFACE ARTIFACT
Occurs in objects of greatly different contrast
INTERFACE ARTIFACT
+ Star pattern artifact is an example of?
INTERFACE ARTIFACT
Compensation: large matrix size & reconstruction algorithm
INTERFACE ARTIFACT
Achieved by choosing a smaller
display FOV
CT MAGNIFICATION
Produces an image with less tissue
per voxel
CT MAGNIFICATION
+Provides a larger image of a smaller
area of interest
CT MAGNIFICATION
+Provides higher resolution
CT MAGNIFICATION
Magnified CT matrix appears?
Pixelated & Less sharp
Can be found in all digital system
+Directly related to the amount of
data collected by the detector
+Comprises 3-5% of the image
Noise
Affects the low contrast resolving
ability of the CT unit
+Noise evaluation: water phantom
+Average Reading: at least 100 pixels
(10x10 matrix)
Noise
+Can be found in all digital system
+Directly related to the amount of
data collected by the detector
+Comprises 3-5% of the image
Noise
+A function of exposure time
+Controlled by the quantity of data
detected
Motion
The last phase in the creation of
the CT image
CT IMAGE DISPLAY
