NONINVASIVE DETERMINATION OF TUMOR OXYGEN-TENSION AND LOCAL VARIATIONWITH GROWTH

Purpose: The objective was to develop and demonstrate a novel noninvas ive technique of measuring regional pO(2) in tumors. The method is bas ed on measuring F-19 nuclear magnetic resonance spin-lattice relaxatio n rate (R(1) = 1/T-1) of perfluorocarbon (PFC) emulsion discretely seq uestered in a tumor. Methods and Materials: We have examined pO(2) in the Dunning prostate tumor R3327-AT1 implanted in a Copenhagen rat. Ox ypherol blood substitute emulsion was administered intravenously and b ecame sequestered in tissue. Proton magnetic resonance imaging (MRI) s howed tumor anatomy and correlated F-19 MRI indicated the distribution of perfluorocarbon. Fluorine-19 spectroscopic relaxometry was used to measure pO(2) in the tumor and repeated measurements over a period of 3 weeks showed the variation in local pO(2) during tumor growth. Resu lts: Perfluorocarbon initially resided in the vascularized peripheral region of the tumor: F-19 nuclear magnetic resonance R(1) indicated pO (2) similar to 75 torr in a small tumor (similar to 1 cm) in an anesth etized rat. As the tumor grew, the sequestered PFC retained its origin al distribution. When the tumor had doubled in size the residual PFC w as predominantly in the core of the tumor and the pO(2) of this region was similar to 1 torr indicating central tumor hypoxia. Conclusion: W e have demonstrated a novel noninvasive approach to monitoring regiona l tumor pO(2). Given the critical role of oxygen tension in tumor resp onse to therapy this may provide new insight into tumor physiology, th e efficacy of various therapeutic approaches, and ultimately provide a clinical technique for assessing individual tumor oxygenation.