Figure 1. Potential interplay between elevated tissue [Na⁺] and cellularity in breast cancer.

A, ²³Na‐MRI images of a mouse mammary tumour (open red arrow), showing elevated [Na⁺] in the tumour compared to healthy contralateral tissue (adapted from James et al., ²⁰²²). B, possible causes of increased tumour [Na⁺]. Left: increased intracellular [Na⁺] must explain the change if the cellularity is increased, and the extracellular fluid volume is decreased. Right: oedema in glioma or necrotic tumours causes an increase in extracellular fluid volume which would increase the total tissue [Na⁺]. C, inverse correlation between tumour [Na⁺] and apparent diffusion coefficient (ADC) which estimates extracellular fluid volume (adapted from James et al., ²⁰²²).