Table 2.

Pathophysiological significance of radiomic features which possibly reflect biological traits of GBM and can be captured on MRI.

Feature category	Descriptor	Intuitive description	Relevance to GBM pathophysiology
Laws features	E5, L5, S5, R5 (combination in both X and Y directions)	E- Edges, L- Level, S- Spots, R- Ripples	Accounting for characteristic qualitative appearance of wave, ripple, edge and spots within an ROI
Gabor features	frequency (0, 4, or 16) and orientation (45°, 90°, 135°, 180°)	This filter bank has characteristics of spatial locality and orientation selectivity	Captures the prominent direction in which the intensity changes occur
Haralick features	Inverse difference moment (IDM)	IDM is a reflection of the presence or absence of uniformity, and hence is a measure of local regions of homogeneity High IDM: Higher presence of locally uniform windows in GLCM. Low IDM: Higher presence of locally heterogeneous windows in GLCM	Captures the underlying lesion heterogeneity
	Correlation	Quantifies the linear patterns in an image based on the distance parameter.	Increased presence of linear patterns yield higher correlation values, lack of image linearity yield lower correlation values
	Sum Entropy	Measure of GLCM relationship to distribution of intensity with respect to entropy (measure of disorder)	Higher entropy is indicative of more chaotic arrangement in areas of high viable cell population
	Sum Variance	Measure of GLCM relationship to distribution of intensity with respect to variance. High sum variance: greater standard deviation of sum average. Low sum variance: low standard deviation of sum average	Possibly accounting for greater variation of scattered atypia and local accumulation of mitotic processes as observed on histopathology.