Table 4.

NGTDM-based features

Name	Definition	Description
NGTDM	$\text{NGTDM}\left(i\right)=\sum _p\sum _q\left\{\begin{array}{c}\left|\overline{M}\left(p,q\right)-i\right|\text{if}I\left(p,q\right)=i\\ 0\text{else}\end{array}\right)$ (with $\overline{M}\left(p,q\right),$ the average of the neighbor voxel intensities)	Higher order, local texture matrix
CoarsenessNGTDM	$\frac{1}{{\sum }_{i}p\left(i\right)\bullet \text{NGTDM}\left(i\right)}$	The level of spatial rate of change in intensity
ContrastNGTDM	$\left[\sum _i\sum _{j}p\left(i\right)\bullet p\left(j\right)\bullet {\left(i-j\right)}^2\right]\bullet \frac{{\sum }_i\text{NGTDM}\left(i\right)}{E\bullet G\bullet \left(G-1\right)}$ (with E = the number of voxels in VOI, G = the number of gray levels)	The intensity difference between neighboring regions of voxels
BusynessNGTDM	$\frac{{\sum }_{i}p\left(i\right)\bullet \text{NGTDM}\left(i\right)}{{\sum }_i{\sum }_j\mid i\bullet p\left(i\right)-j\bullet p\left(j\right)\mid }$ (with p(i) ≠ 0, p(j) ≠ 0)	The spatial frequency of changes in intensity

NGTDM neighborhood gray-tone difference matrix