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one of the 256 shades of gray. Vary the gray scale window width and level to select anatomy for
display. Window Width determines the quantity of gray pixel values. Window Level selects the
center Window Width pixel value.
Example: Two windows may contain identical widths of 100 values, but display completely
different anatomy, because one has a level of -100 and the other has a level of 150.
16.6.1 CT Number Mean and Standard Deviation
•
An ROI averages the values of the enclosed pixels, and displays the resulting Mean value.
•
Standard Deviation describes the difference between the minimum and maximum ROI
value.
•
A large ROI provides a larger, more accurate statistical sample than a small ROI.
The system provides, using the image display software, the capability to draw and edit
rectangular and elliptical regions of interest (ROI), with the ability to calculate and report the
mean value and standard deviation of the image pixel data contained within the ROI and the
area of the ROI.
It also provides the capability to draw and edit a circular region of interest, with the ability to
calculate and report the mean value, standard deviation, minimum, maximum and area (mm
the image pixel data contained within the ROI.
16.6.2 CT Number Accuracy
CT Number of water: 0 HU ± 3 HU
CT Number of air: –1000 HU ± 10 HU
16.7 Range, Precision and Accuracy of Displayed Values
Table 3: Range, precision and accuracy of displayed values
Primary Gantry Display
Vertical height indicator
Horizontal cradle position
Scannable Range
Secondary Gantry Display
Prep Delay Timer
Breath hold timer
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Direction 5480385-1EN, Revision 1
Range, Precision, Accuracy
Display Range: 0 to 999.9 mm
Display Precision: +/-1.5 mm
Display Accuracy: +/-1.5 mm
Display Range: 0 to 9999.9 mm
Display Precision: +/-.25 mm
Display Accuracy: +/- 0.06 %
Display Range: 0 to 9999.9 mm
Display Precision: +/-.25 mm
Display Accuracy: +/- 0.06 %
Range, Precision, Accuracy
Display Range: 0 - 999 s
Display Precision: +/- 1 s
Display Accuracy: +/- 1 s
Display Range: 0 - 99 s
Display Precision: +/- 1 s
Display Accuracy: +/- 1 s
16 Accuracy of Measurements
Revolution CT User Manual
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Troubleshooting
