Table 3.

The R1 Features (%Diff < 10%) for CT and PET.

Subtype	Feature	3D CT	4D CT	3D PET	4D PET
Shape	Volume	✓	✓	✓	✓
	Surface area		✓	✓	✓
	Surface area/volume	✓	✓	✓	✓
	Sphericity		✓	✓	✓
	Compactness	✓	✓	✓	✓
	Spherical disproportion	✓	✓	✓	✓
	Long axis	✓	✓	✓	✓
	Short axis		✓	✓	✓
	Eccentricity			✓	✓
	Convexity	✓	✓	✓	✓
Intensity	Minimum intensity	✓	✓	✓	✓
	Maximum intensity		✓	✓	✓
	Peak intensity	✓	✓	✓	✓
	Mean intensity	✓	✓	✓	✓
	Standard deviation			✓	✓
	Coefficient of variation			✓	✓
	TGV (Total Summed Intensity)	✓	✓	✓	✓
	RMS	✓	✓	✓	✓
	I30	✓	✓	✓	✓
	I10-I90			✓	✓
	V10-V90		✓	✓	✓
	First-order energy		✓	✓	✓
	First-order entropy	✓	✓	✓	✓
	First-order contrast		✓	✓	✓
	First-order local homogeneity			✓	✓
	Histogram entropy		✓	✓	✓
	Uniformity			✓	✓
GLCM	Homogeneity			✓	✓
	Second-order entropy			✓	✓
	Dissimilarity			✓	✓
	Co-occurrence mean		✓	✓	✓
	Inverse difference moment	✓	✓	✓	✓
	Inverse difference	✓	✓	✓	✓
	Sum average		✓	✓	✓
	Sum entropy			✓	✓
	Difference average			✓	✓
	Difference variance			✓	✓
	Difference entropy			✓	✓
	Info correlation 1			✓	✓
	Info correlation 2			✓	✓
RLM	SRE	✓	✓	✓	✓
	LRE		✓	✓	✓
	HGRE				✓
	SRHGE				✓
	LRHGE
	GLNU			✓	✓
	RLNU			✓	✓
	RPC	✓	✓	✓	✓
GLSZM	ZP			✓	✓

Abbreviations: CT, computed tomography; 3D, 3-dimensional; 4D, 4-dimensional; GLCM, gray-level co-occurrence matrix; GLNU, gray level nonuniformity; GLSZM, gray-level size zone matrix; HGRE, high gray-level run emphasis; LRE, long-run emphasis; LRHGE, long-run high gray-level emphasis; PET, positron emission tomography; RLM, run length matrix; RLNU, run length nonuniformity; RMS, root mean square; RPC, run percentage; SRE, short run emphasis; SRHGE, short-run high gray-level emphasis; ZP, zone percentage.