Diffusion-weighted imaging in Brain tumors

 DWI measures the random Brownian motion of water molecules in tissues and can hence assess tissue microstructure and tumor cellularity based on the apparent diffusion coefficient (ADC).[5] Lower ADC values correspond to well-organized tissue and high cellularity; higher ADC values correspond to low cellularity and not well-organized tissue. Thus high-grade or very cellular tumors (eg, lymphoma, Figure 4) may show lower ADC values. Similarly, increasing ADC values after treatment might indicate treatment response because tumor cell density decreases with cell death and leads to increase in the extravascular extracellular space (EES). However, there is considerable overlap, and thus the ADC value alone may be insufficient to predict the tumor grade.