16 Accuracy of Measurements
This section includes information on accuracy of measurements used when reviewing images.
16.1 Measure Distance for Axial, Helical, and Cine Images
CAUTION
Measure error using the straight line distance graphic is ± the largest voxel
dimension.
CAUTION
Note that the measurements are accurate only if the trace segments are longer
than the slice interval.
16.2 Measure Distance for Scout Images
Accuracy of measurements for scout images in the “X” direction varies with object thickness and
distance from ISO center in the “Y” direction. Note the orientations of the “X” and “Y” in
Illustration 31 below assume a scout scan plane of 0 degrees. If the scout plane is rotated, then
the “X” and “Y” orientation changes accordingly.
•
For measurements of anatomy in the “X” direction that are at ISO center (“Y”):
The measure error using the straight line distance graphic is less than 5 % of the measured
distance plus 2 mm.
•
For measurements of anatomy in the “X” direction that are NOT at ISO (“Y”):
The measure error using the straight line distance graphic is less than 5 % of the measured
distance plus 2 mm plus 3 % of measured distance per centimeter from ISO.
•
For measurements of anatomy in the “Z” direction:
Measure error using the straight line distance graphic is less than two times the image pixel
size.
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Chapter 3 Safety 89
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