A noninvasive tumor oxygenation imaging strategy using magnetic resonance imaging of endogenous blood and tissue water

Purpose To present a novel imaging strategy for noninvasive measurement of tumor oxygenation using MR imaging of endogenous blood and tissue water. Theory and Methods The proposed approach for oxygen partial pressure (pO₂) estimation is based on intravoxel incoherent motion diffusion MRI and the dependence of the blood R₂ relaxation rate on the inter-echo spacing measured using a multiple spin-echo Carr-Purcell-Meiboom-Gill sequence and weak-field diffusion model. The accuracy of the approach was validated by comparison with ¹⁹F MRI oximetry. Results The results in eight rats at 4.7 T showed that tumors have longer T₁ (1980 ± 186 ms) and T₂ (59 ± 9 ms) relaxation times, heterogeneous blood volume fraction (0.23 ± 0.1), oxygen saturation level (Y) (0.53 ± 0.12), and pO₂ (36 ± 15 mmHg) distributions compared with normal muscle (T₁ 1480 ± 86 ms, T₂ 29 ± 2 ms, blood volume fraction 0.22 ± 0.03, Y 0.49 ± 0.06, and pO₂ 39 ± 5 mmHg). pO₂ estimates based on the novel ¹H approach were essentially identical with ¹⁹F observations. Conclusion The study indicates that noninvasive measurement of tumor pO₂ using ¹H MRI derived multiparametric maps is feasible and could become a valuable tool to evaluate tumor hypoxia.