Figure 5.

Coronal projections of compartmentalized ²³Na signals (Na⁺_b, Na⁺_e, Na⁺_i) as well as transendothelial (ΔNa⁺_end) and transmembrane (ΔNa⁺_mem) gradients in an RG2 tumor. (a) Axial ¹H-MRI indicating the tumor (white outline) across slices (same as Fig. 4), where the yellow line indicates the position for a coronal projection. (b) Spatially varying ²³Na signals for Na⁺_b, Na⁺_e, and Na⁺_i are shown with blue, orange, and yellow lines, respectively, where the vertical black lines indicate the tumor boundary. The Na⁺_b signal (blue) is clearly elevated in the tumor, and most elevated in slices 1–4 (or superficially). Behavior of Na⁺_b signal (blue) is inversely related to Na⁺_e signal (orange), which is high outside the tumor and weaker inside the tumor. While intratumoral Na⁺_b signal (blue) is high in slices 1–4, the peritumoral Na⁺_e signal (orange) is highest in slices 3–4. Comparatively, the Na⁺_i signal (yellow) does not vary significantly across slices, but slightly lower inside the tumor than outside the tumor. (c) Behaviors of ∆Na⁺_mem (green) and ∆Na⁺_end (magenta) signals closely mimic patterns of Na⁺_e and Na⁺_b signals, respectively, indicating that each of those Na⁺ compartments is the primary driver of the respective Na⁺ gradient. See Figure S5 for a similar example for a U87 tumor.