gms | German Medical Science

Objective: Since hypoxia makes tumors more aggressive and therapy resistant, characterizing blood supply and oxygen consumption may be a crucial information for therapy planning and outcome prediction. While the mapping of blood perfusion by arterial spin labeling (ASL) is an established and proven method, the mapping of oxygen consumption by MRI remains challenging. However, a new promising method: QUantitative Imaging of eXtraction of oxygen and Tissue consumption (QUIXOTIC) may be able to allow for robust and reliable oxygen consumption mapping. Therefore, the purpose of this study was to test the ability of the QUIXOTIC method to map the tumor oxygen consumption in conjunction with ASL in glioma patients.

Method: 14 patients, 6 with high grade and 8 with low-grade gliomas, were scanned at 3T. Fluid attenuated inversion recovery (FLAIR) images were used to define the tumor and gray matter control region of interest (ROI). Pseudo continuous arterial spin labeling (pCASL) was used to map cerebral blood flow (CBF) and the QUIXOTIC method to map the oxygen extraction fraction (OEF). After co-registering FLAIR, pCASL and QUIXOTIC images maps of cerebral metabolic rate of oxygen (CMRO₂) were calculated. To account for tumor heterogeneity, only voxels with the highest 10% of the measured (high-)OEF/CBF values and their corresponding (corr-)CBF/OEF values were averaged and analyzed, respectively.

Results: Parameter maps reveal strong tumor heterogeneity with high variation in OEF, CBF and CMRO₂. Higher high-OEF was found for high and low grade gliomas compared to GM control with the corresponding corr-CBF similar for both glioma grades and GM control. High-CBF was lower for high-grade gliomas compared to low-grade gliomas and GM control, whereas corr-OEF was lower for both glioma grades compared to GM control. All parameters were reasonably stable for GM control and showed lower variability as compared to the gliomas.

Conclusions: The observed trends of lower corr-CBF with high-OEF and lower corr-OEF with high-CBF are physiologically reasonable, especially for the GM control where a stable and homogeneous CMRO₂ is a valid assumption. The high high-OEF also found for low-grade gliomas is very interesting, since it suggests, that even low grade gliomas may possess hypoxic regions, which are difficult to detect with other blood oxygenation sensitive MRI methods. These findings suggest that the QUIXOTIC method is able to map tumor oxygen metabolism.