Figure 3.

Region of interest (ROI) analysis for the average relaxation rate (R₂) and extracellular pH (pH_e) before and after infusion of SPIO-NPs for all RG2 tumor-bearing rats that underwent coinfusion of TmDOTP⁵⁻ and probenecid (n = 5). The ROI analysis is based on concentric 1 mm circular rings drawn from the center of mass of the tumor. (a) Average R₂ values in different ROIs for intrinsic contrast, after infusion of TmDOTP⁵⁻, and after infusion of TmDOTP⁵⁻ with SPIO-NPs. The average R₂ enhancement was highest inside the tumor (ROIs 1–3) compared to tumor edge (ROI 4) and nontumor regions (ROIs 5–9). The dashed line represents the tumor edge. Small R₂ enhancement was observed after infusion of TmDOTP⁵⁻. However, much higher R₂ enhancement was observed upon infusion of SPIO-NPs. See Table 1 for details. (b) The average pH_e values in different ROIs before and after infusion of SPIO-NPs. The pH_e values measured before and after infusion of SPIO-NPs were similar, both inside and outside the tumor. The pH_e was lowest in the tumor and highest in the healthy/nontumor tissue farthest from the tumor. Low pH_e was also measured on the tumor margin. See Table 2 for details.