Fig 6. Using a threshold for low and high tracer uptake of SUV = 3.6 for ¹⁸F-FDG and ADC = 1.5x10^-3 mm²/s for restricted and less restricted water diffusivity, up to four tumor cluster of different biologically activity could be defined.

Here, the relative distribution (%) of the different cluster from the tumor periphery to the center is shown. The relative number of voxels with high uptake of ¹⁸F-FDG and lower ADC values (yellow, vital tumor) decreases to the tumor center, oppositely for voxels with low uptake of ¹⁸F-FDG and lower ADC values (turquoise, high density of cells with low tumor activity or low density of tumor cells but dense tumor stroma caused by desmoplastic reactions). Voxels from the clusters with less restricted water diffusivity (SUV_high respectively SUV_low) can be found in all tumor parts, indicative either for hypoxia (SUV_high, red) or necrosis (SUV_low, white). However, the highest amount of voxels from the SUV_high/ADC_high cluster can be found within the transitional zone, whereas the voxel of the SUV_low/ADC_high cluster increase to central tumor parts.