Tumour oxygen dynamics measured simultaneously by near-infrared spectroscopy and ¹⁹F magnetic resonance imaging in rats

Simultaneous near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI) were used to investigate the correlation between tumour vascular oxygenation and tissue oxygen tension dynamics in rat breast 13762NF tumours with respect to hyperoxic gas breathing. NIRS directly detected global variations in the oxygenated haemoglobin concentration (Δ[HbO ₂]) within tumours and oxygen tension (pO₂) maps were achieved using ¹⁹F MRI of the reporter molecule hexafluorobenzene. Multiple correlations were examined between rates and magnitudes of vascular (Δ[HbO₂]) and tissue (pO₂) responses. Significant correlations were found between response to oxygen and carbogen breathing using either modality. Comparison of results for the two methods showed a correlation between the vascular perfusion rate ratio and the mean pO₂ values (R² > 0.7). The initial rates of increase of Δ[HbO ₂] and the slope of dynamic pO₂ response, d(pO ₂)/dt, of well-oxygenated voxels in response to hyperoxic challenge were also correlated. These results demonstrate the feasibility of simultaneous measurements using NIRS and MRI. As expected, the rate of pO₂ response to oxygen is primarily dependent upon the well perfused rather than poorly perfused vasculature.