Combined endogenous MR biomarkers to predict basal tumor oxygenation and response to hyperoxic challenge

Hypoxia is a common feature of solid tumors, which translates into increased angiogenesis, malignant phenotype cell selection, change in gene expression and greater resistance to radiotherapy and chemotherapy. Therefore, there is a need for markers of hypoxia to stratify patients, in order to personalize treatment to improve therapeutic outcome. However, no modality has yet been validated for the screening of hypoxia in routine clinical practice. Magnetic resonance imaging (MRI) R1 and R2* relaxation parameters are sensitive to tissue oxygenation: R1 is sensitive to dissolved oxygen and R2* is sensitive to intravascular deoxyhemoglobin content. Two rat tumor models with distinct levels of hypoxia, 9L–glioma and rhabdomyosarcoma, were imaged for R1 and R2* under air and carbogen (95% O2 and 5% CO2) breathing conditions. It was observed that the basal tumor oxygenation level had an impact on the amplitude of response to carbogen in the vascular compartment (R2*), but not in the tissue compartment (R1). In addition, the change in tissue oxygenation estimated by ΔR1 correlated with the change in vascular oxygenation estimated by ΔR2*, which is consistent with an increase in oxygen supply generating an elevated tumor pO2. At the intra‐tumoral level, we identified four types of voxel to which a hypoxic feature was attributed (mild hypoxia, severe hypoxia, normoxia and vascular steal), depending on the carbogen‐induced change in R1 and R2* values for each voxel. The results ...
Source: NMR in Biomedicine - Category: Radiology Authors: Tags: RESEARCH ARTICLE Source Type: research