Spatial heterogeneity of the metabolic response of RIF‐1 tumors to a vasoactive agent evaluated in vivo by one‐dimensional ³¹P chemical‐shift imaging

Localized ³¹P NMR spectroscopy was used to evaluate the spatial heterogeneity of the metabolic response of RIF‐1 tumors to hydralazine. Volume localized ³¹P spectra were obtained from subcutaneous RIF‐1 tumors using one‐dimensional chemical‐shift imaging, before and 20 min after treatment with 5 mg/kg hydralazine, administered intravenously. Following treatment all of the tumors showed an overall decrease in the ratio of nucleoside triphosphate (NTP) to inorganic phosphate (P_i) and a decrease in pH. However, spatial localization revealed that the reduction in NTP/P_i was not uniform within some tumors. This was partly due to regional differences in the levels of metabolites existing before treatment. Normal tissue adjacent to the tumor did not show a significant decrease in high‐energy metabolites or pH.