Magnetic Resonance Imaging (MRI)

Dynamic Contrast-Enhanced MRI (DCE MRI)

In this technique fast repeated images are acquired before, during and after the rapid administration of a small hydrophilic gadolinium-based contrast agent, which diffuses through blood vessel walls and distributes into the extracellular space. The change in signal intensity reflects tumour perfusion, vessel permeability and the volume of extracellular space (Turkbey et al. 2010). It does not correlate directly with tissue pO2 levels but a small study in HNSCC found positive correlation between imaging parameters of poor perfusion and pimonidazole staining (Newbold et al. 2009), and with hypoxia defined by ¹⁸F-fluoromisonidazole PET uptake in nodal metastases (Jansen et al. 2010).

Blood Oxygen Level-Dependent MRI (BOLD MRI)

This is an indirect measure of visualising pO₂ in blood vessels and surrounding tissue based on the paramagnetic properties of deoxyhaemoglobin, which is related to tissue oxygenation. It does not provide quantitative information on oxygen concentration and the signal can be influenced by many factors such as blood flow and pH. However, studies have shown correlation between this technique and polargraphic electrode pO₂ measurements and pimonidazole staining in prostate cancer, suggesting BOLD MRI may provide complementary information related to tissue oxygenation (Chopra et al. 2009).