Measurements of venous oxygen saturation in the superior sagittal sinus using conventional 3D multiple gradient‐echo MRI: Effects of flow velocity and acceleration

Purpose This work investigates the effects of flow acceleration in the superior sagittal sinus on slice‐dependent variations in venous oxygen saturation (SvO 2 ) estimations using susceptibility‐based MR oximetry. Methods Three‐dimensional multiple gradient‐echo images, with first‐order flow compensation along the anterior–posterior readout direction for the first echo, were acquired twice from 15 healthy volunteers. For all slices, phases within the superior sagittal sinus were fitted using linear regression across four TEs to obtain the Pearson’s correlation coefficients (PCCs), the largest of which corresponded to minimum acceleration influence. SvO 2 derived from odd echoes on this slice was used to assess interscan difference, and compared with the central 15th slice for slice‐dependent difference, both using Bland‐Altman analysis. Within‐scan interslice SvO 2 consistency was examined versus PCC. Multislice‐averaged SvO 2 values were then computed from slices with PCCs above a certain threshold. Results Slice‐dependent difference in SvO 2 varied from −16.2% to 21.5% at two SDs, in agreement with a recent report, and about twice larger than interscan differences for the automatically selected slice (−7.5% to 10.3%) and for the central 15th slice (−8.0% to 8.8%). For slices with PCCs higher than −0.98, interslice SvO 2 deviations were all found to be less than 5.0%. Multislice‐averaged SvO 2 with PCCs higher than −0.98 further reduced interscan difference to −4.7% to 8.2%. Conclusion Slice‐dependent variations in SvO 2 may partly be explained by the effects of flow acceleration. Our method may enable conventional 3D multiple gradient echo to be used for SvO 2 estimations in the presence of pulsatile flow.