Statistics Measures

Except for the Pixel Dump different levels of statistics can be collected:

Statistics: Standard descriptive statistics measures.
Statistics + Surface + Sphericity: Standard descriptive statistics measures, a VOI surface estimate and an index of how sphere-shaped the VOI is.
Statistics + Surface + Sphericity + Diameter: As above, plus the maximum VOI diameter.

The selected statistic type is calculated for each VOI.

Statistics Measures

The following basic descriptive statistics are calculated using the values of all pixel classified for a VOI. With binary classifications each included pixel contributes equally.

With the Fraction mode classification, however the contribution of a pixel is proportional to the fractional area f_i included in the contour (f_i.=1 fully included, f_i.=0.5 50% included). This weighting applies for the Average, the Standard Deviation, the Volume, the Total and the AUC. For the other measures, which don't support fractional contributions, only the pixels with f_i.>0.5 are used.

Notes:
1. Due to calculation of the fractional area, statistics using the Fraction mode is substantially more time-consuming.
2. The fraction mode is not effective for automatically generated VOIs (iso-contouring, atlases), because the contours follow the pixel boundaries.

Averaged	Average of the pixel values. Fraction mode: Sum(f_i*v_i)/Sum(f_i). v_ivalue of pixel i.
Sd	Population standard deviation of the pixel values. Fraction mode: a weighted standard deviation is calculated accounting for the pixel area included in the contour.
Stdv	Sample standard deviation of the pixel values. Fraction mode: analogous to Sd.
Volume	Volume of the VOI pixels. It is based on the pixel size in x and y and the slice thickness in z. Fraction mode: Sum(f_i)*pixel-volume.
Total(SUM)	Sum of the pixel values. The interpretation depends on the image contents. In the case of activity units the result will be total activity in the VOI. Fraction mode: Sum(f_i*v_i)
*Total(AVRVOL)**	Average of the pixel values multiplied by the VOI volume. The interpretation depends on the image contents. In the case of activity concentration units, the result represents total activity in the VOI. Fraction mode: Sum(f_iv_i)pixel-volume In the case of SUV units, the result is called Total Lesion Glycolysis (TLG). The TLG is usually calculated in combination with a lower range.
Min	Minimum pixel value. Fraction mode: Considers pixels with f_i.>0.5.
Max	Maximum pixel value. Fraction mode: Considers pixels with f_i.>0.5.
NumberOfPixels	Number of pixels included in the VOI. Fraction mode: Considers pixels with f_i.>0.5.
NumberOfEffectivePixels	Fraction mode: Sum(f_i). Otherwise equal to NumberOfPixels.
HotAveraged	The highest pixel values averaged. The default Number of Hottest Pixels values to be averaged can be set in the User configuration, and can be changed in the upper part of the statistics window. Fraction mode: Considers pixels with f_i.>0.5.
Q1	First quartile of the VOI pixel values. Fraction mode: Considers pixels with f_i.>0.5.
Median	Median value of the VOI pixel values. Fraction mode: Considers pixels with f_i.>0.5.
Q3	Third quartile of the VOI pixel values. Fraction mode: Considers pixels with f_i.>0.5.
AreaUnderCurve	Static data: Averaged times frame duration. Fraction mode: Sum(f_iv_it)/Sum(f_i) (t = acquisition duration). Dynamic data: Integral of the Averaged curve.

Additional Measures

The following additional VOI measures can be obtained with the corresponding statistics button:

SurfaceArea	Estimate of the VOI surface which is obtained by triangulating the contours and accumulating the triangle areas. Fraction mode: Considers pixels with f_i.>0.5.
Spericity	Index of how spherical a VOI is. The values range between 0 and 1 (perfect sphere). Wikipedia. Fraction mode: Considers pixels with f_i.>0.5.
DiameterMax	Maximal distance between any two pixels in the VOI. The calculation can take substantial time and is restricted to VOIs enclosing less than 100'000 pixels. Fraction mode: Considers pixels with f_i.>0.5.