Introduction
Global oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) were quantified in a test–retest study. Cerebral blood flow (CBF) data, required for CMRO2 estimation, were obtained using dynamic susceptibility contrast MRI (DSC‐MRI). OEF and CMRO2 were quantified using two separate data sets, that is, conventional high‐resolution (HR) gradient echo (GRE) phase maps as well as echo planar imaging (EPI) phase maps taken from the baseline (precontrast) part of the DSC‐MRI time series. The EPI phase data were included to elucidate whether an extra HR‐GRE scan is needed to obtain information about OEF and CMRO2, or if this information can be extracted from the DSC‐MRI experiment only.
Methods
Twenty healthy volunteers were scanned using 3 T MRI on two occasions. Oxygen saturation levels were obtained from phase data measured in the great cerebral vein of Galen, based on HR‐GRE as well as EPI phase maps. In combination with DSC‐MRI CBF, this allowed for calculation of OEF and CMRO2.
Results
High‐resolution‐gradient echo‐ and EPI‐based phase images resulted in similar OEF spread and repeatability, with coefficients of variation/intraclass correlation coefficients of 0·26/0·95 and 0·23/0·81, respectively. Absolute OEF values (HR‐GRE: 0·40 ± 0·11, EPI: 0·35 ± 0·08) were consistent with literature data. CMRO2 showed similar repeatability, somewhat increased spread and reasonable absolute values (HR‐GRE: 3·23 ± 1·26 ml O2/100 g min−1, EPI: 2·79 ± 0·89 ml O2/100 g min−1).
Discussion
In general, the results obtained by HR‐GRE and EPI showed comparable characteristics. The EPI methodology could potentially be improved using a slightly modified DSC‐MRI protocol (e.g. with regard to spatial resolution and slice gap).