Direct 17O MRI with partial volume correction: first experiences in a glioblastoma patient

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Abstract
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.

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