Fig. 3

Axial, coronal and sagittal images of ¹H, ultrashort TE (UTE)/single-quantum (SQ)/triple-quantum-filtered (TQF) ²³Na (left), co-registered MR (bottom left) and [¹⁸F]FET-PET images (bottom right) of tumour (pointed out by the red arrow) in vivo rat brain (rat²) together with ³¹P MR spectrum with fitting (top right) where the shim-adjusting volume (green box) and ³¹P voxel localisation (yellow box) are shown. ²³Na images acquired using UTE, SQ and TQ represent total ²³Na concentration-weighted, non-restricted (mainly extracellular) and restricted (mainly intracellular) ²³Na, respectively