Direct estimation of 17 O MR images (DIESIS) for quantification of oxygen metabolism in the human brain with partial volume correction.

ABSTRACT

PURPOSE: To provide a data post-processing method that corrects for partial volume effects (PVE) and fast T 2 * decay in dynamic 17 O MRI for the mapping of cerebral metabolic rates of oxygen consumption (CMRO2 ). METHODS: CMRO2 is altered in neurodegenerative diseases and tumors and can be measured after 17 O gas inhalation using dynamic 17 O MRI. CMRO2 quantification is difficult because of PVE. To correct for PVE, a direct estimation of the MR images (DIESIS) method is proposed and used in 4 dynamic 17 O MRI data sets of a healthy volunteer acquired on a 3T MRI system. With DIESIS, 17 O MR signal time curves in selected regions were directly estimated based on parcellation of a coregistered 1 H MPRAGE image. RESULTS: Profile likelihood analysis of the DIESIS method showed identifiability of CMRO2 . In white matter (WM), DIESES reduced CMRO2 from 0.97 ± 0.25 µmol/gtissue /min with Kaiser-Bessel gridding reconstruction to 0.85 ± 0.21 µmol/gtissue /min, whereas in gray matter (GM) it increases from 1.3 ± 0.31 µmol/gtissue /min to 1.86 ± 0.36 µmol/gtissue /min; both values are closer to the literature values from the 15 O-PET studies. CONCLUSION: DIESIS provided an increased separation of CMRO2 values in GM and WM brain regions and corrected for partial volume effects in 17 O-MRI inhalation experiments. DIESIS could also be applied to more heterogeneous tissues such as glioblastomas if subregions of the tumor can be represented as additional parcels.