CORRELATION OF MAGNETIC-RESONANCE AND OXYGEN MICROELECTRODE MEASUREMENTS OF CARBOGEN-INDUCED CHANGES IN TUMOR OXYGENATION

Purpose: The aim of this work was to test the hypothesis that decrease s in the linewidth of magnetic resonance (MR) water signals in tumors caused by oxygenating treatments are due to increases in capillary and venous oxygen saturation of hemoglobin, which are tightly coupled to increases in extravascular oxygen tension (pO(2)). To establish this l ink, changes measured by MR were compared to changes in tissue pO(2) m easured directly by oxygen microelectrodes during carbogen (95% O-2/5% CO2) inhalation. Methods and Materials: Mammary adenocarcinomas (R323 0AC) in nine rats were imaged at 4.7 Tesla, T-1-weighted (TR = 200 ms, flip angle = 45 degrees) spectroscopic images of the water resonance in a single slice through each tumor were acquired with spectral resol ution of 3.9 Hz and bandwidth of +/-1000 Hz, In the same slices in the se tumors, microelectrode measurements were made using a non-Clark sty le oxygen electrode with a 350-micron tip. MR and microelectrode measu rements were made during alternating periods of air and carbogen inhal ation. Results: Water resonance linewidth decreased significantly duri ng carbogen-induced hyperoxia, Paired Student's t-test analysis of mic roelectrode data indicated that pO(2) was significantly (p < 0.05) inc reased as a result of carbogen inhalation, MR and microelectrode data averaged over each tumor demonstrated that decreased MR water signal l inewidth is strongly correlated (r = 0.92, p < 0.05) with increased tu mor pO(2) levels. Conclusion: Although tumor oxygenating agents increa se response to radiation in rodent tumors, clinical studies have shown only marginal effects on the radiosensitivity of human tumors. This m ay be, in part, because the effects of tumor oxygenating treatments ar e highly heterogeneous both within each tumor and among a population o f tumors. The noninvasive, high-resolution MR methods that are validat ed by the present work could guide the design of new and more effectiv e tumor oxygenating agents and optimize treatments for individual pati ents. (C) 1998 Elsevier Science Inc.