Table 2. Detailed definitions of first-order features.

Feature	Explanation
Mean	The average gray-level intensity within the ROI
Minimum	Minimum = min(X)
Maximum	The maximum gray-level intensity within the ROI
10th	The 10th percentile of X
Median	The median gray-level intensity within the ROI
90th	The 90th percentile of X
Range	The range of gray values in the ROI
Interquartile range	Interquartile range = P75−P25
Energy	A measure of the magnitude of voxel values in an image
Total energy	The value of energy feature scaled by the volume of the voxel in cubic mm
Entropy	The uncertainty/randomness in the image values
Kurtosis	A measure of the “peakedness” of the distribution of values in the image ROI
Skewness	The asymmetry of the distribution of values about the mean value
Uniformity	A measure of the sum of the squares of each intensity value
Variance	The mean of the squared distances of each intensity value from the mean value
Mean absolute deviation	The mean distance of all intensity values from the mean value of the image array
Robust mean absolute deviation	The mean distance of all intensity values from the mean value calculated on the subset of image array with gray levels in between or equal to the 10th and 90th percentile
Root mean squared	The square root of the mean of all the squared intensity values

The information above has been taken from the official Pyradiomics website (https://pyradiomics.readthedocs.io/en/latest/features.html). ROI, region of interest.