Supplementary material
The computation of the four principal components requires the following steps:
1) cubic root transformation of all 18F-FDG PET variables and natural logarithmic transformation to all 68Ga-DOTATOC PET variables;
2) standardization of the variables using the means and standard deviations reported in Table S1;
3) calculation of the components as a linear combination of the transformed and standardized PET variables, by using the coefficients (called loadings) in Table S2.
Table S1. Mean and standard deviation (SD) of all PET variables after the first transformation.
PET variables mean SD
68Ga-DOTATOC PET
IV 2.2292 0.7226
SZV 5.3686 1.2435
ZP -1.5157 0.4841
Entropy 1.8753 0.1761 Homogeneity -1.4710 0.3564 Dissimilarity 2.1725 0.7121 Co-V -0.1478 0.4188 SUVmax 3.8980 0.8139
SRD 2.9885 1.4625
18F-FDG PET
IV 1.5277 1.1461
SZV 3.1518 2.6024
ZP 0.3753 0.2579
Entropy 1.2372 0.7997 Homogeneity 0.4773 0.3177 Dissimilarity 1.1751 0.8676
Co-V 0.5287 0.3455
SUVmax 1.5073 0.9943
MTV 1.9642 1.6654
Table S2. Principal component analysis loadings.
PET variables PC1 PC2 PC3 PC4
68Ga-DOTATOC PET
IV 0.1566 0.1114 0.5071 -0.2068 SZV 0.2052 0.3255 0.2146 -0.0728 ZP 0.0604 0.3158 -0.2397 0.4207 Entropy 0.1734 0.3794 0.0386 0.0796 Homogeneity -0.0978 -0.3667 0.1995 -0.3235 Dissimilarity 0.0533 0.4048 -0.2620 0.0530 Co-V 0.0116 0.2154 -0.3094 -0.5931 SUVmax 0.1048 0.2823 -0.1794 -0.5286 SRD 0.1221 0.2620 0.4250 0.0883
18F-FDG PET
IV 0.3331 -0.0511 0.1242 -0.0155 SZV 0.3052 -0.1262 0.1128 -0.1026 ZP 0.2806 -0.1928 -0.2437 0.0229 Entropy 0.3231 -0.1344 -0.1049 -0.0048 Homogeneity 0.3184 -0.0539 -0.0723 0.0433 Dissimilarity 0.2541 -0.2063 -0.2543 0.0462 Co-V 0.3224 -0.1311 -0.1110 0.0060 SUVmax 0.3268 -0.0914 -0.0644 0.0110 MTV 0.3118 0.0134 0.1899 0.0823
