Stefan H. Hoffmann

In tumor cells the energy production is shifted from aerobic to anaerobic metabolization of glucose, which makes the cerebral metabolic rate of oxygen consumption (CMRO₂) a diagnostic parameter for tissue viability. Direct oxygen-17 (¹⁷O) MRI during inhalation of ¹⁷O gas allows for a non-invasive determination of the CMRO₂. However, the low spatial resolution and the fast transverse relaxation of ¹⁷O lead to partial volume effects that severely bias the quantification of signal intensities. The aim of this work was to determine the CMRO₂ in a tumor patient by ¹⁷O MRI in combination with a partial volume correction (PVC) scheme. Direct ¹⁷O MRI was performed in a glioblastoma patient (F, 51 years) prior to surgery at 7 T. The ‘geometric transfer matrix’ algorithm for volume of interest based PVC was adapted to ¹⁷O MRI to recover the true signal intensities. We determined the CMRO₂ values of gray matter (GM), white matter (WM), cerebrospinal fluid (CSF) and the tumor areas of the contrast enhancing rim (CE), the necrotic center (NE), and the perifocal edema (PE) using a three-phase metabolic model. Large differences in the signal increase during ¹⁷O₂ inhalation were obtained ranging from less than 2 % in the tumor center up to more than 20 % in GM areas. After PVC of the signal time curves, we determined CMRO₂ values of 0.67 ± 0.08 μmol/g/min (WM), 3.57 ± 0.67 μmol/g/min (GM), 0.35 ± 0.09 μmol/g/min (CE), and 0.42 ± 0.05 μmol/g/min (PE). In CSF and NE no oxygen uptake (i.e. CMRO₂ = 0) was determined from the corrected signals, well in accordance with the underlying physiology in these regions. The results show that PVC has a strong effect on the resulting CMRO₂ values obtained by ¹⁷O MRI. We found substantial differences—especially in GM tissue—between corrected and non-corrected CMRO₂ values. Additionally, we demonstrated the feasibility of CMRO₂ assessment in a glioblastoma patient by ¹⁷O MRI.