Table 1. Relationship between the degree of water diffusivity and glucose metabolism, and their potential biological correlate.

Diffusivity of water DW-MRI	Glucose metabolism 18F-FDG PET	Hypothetical biological correlate
Restricted	Intense	Vital, oxygenated tumor with high density of viable tumor cells
Restricted	Low	High density of tumor cells with low activity resp. hibernating tumor cells or low density of tumor cells but dense tumor stroma caused by desmoplastic reactions
Not / less restricted	Low	Macroscopic necrosis
Not / less restricted	Moderate—intense	Lower cell density but still high glucose metabolism, maybe due to cell edema or regions of micronecrosis and potentially hypoxia