FIGURE 6.  Plot of equilibrium distribution volume (V_ed = k₁/k₂) for newly diagnosed tumors. High- and low-grade tumors formed separate subgroups. High grade: 4 patients with 9 tumors. Low grade: 5 patients with 7 tumors. 2C = 2-compartment model; 3C– = 3-compartment model without metabolite correction; 3C+ = 3-compartment model with metabolite correction.