Investigating hyperoxic effects in the rat brain using quantitative susceptibility mapping based on MRI phase

Abstract

Purpose: To test whether susceptibility imaging can detect microvenous oxygen saturation changes, induced by hyperoxia, in the rat brain.

Methods: A three-dimensional gradient-echo with a flow compensation sequence was used to acquire T2*-weighted images of rat brains during hyperoxia and normoxia. Quantitative susceptibility mapping (QSM) and QSM-based microvenous oxygenation venography were computed from gradient-echo (GRE) phase images and compared between the two conditions. Pulse oxygen saturation (SpO₂ ) in the cortex was examined and compared with venous oxygen saturation (SvO₂ ) estimated by QSM. Oxygen saturation change calculated by a conventional Δ R2* map was also compared with the ΔSvO₂ estimated by QSM.

Results: Susceptibilities of five venous and tissue regions were quantified separately by QSM. Venous susceptibility was reduced by nearly 10%, with an SvO₂ shift of 10% during hyperoxia. A hyperoxic effect, confirmed by SpO₂ measurement, resulted in an SvO₂ increase in the cortex. The ΔSvO₂ between hyperoxia and normoxia was consistent with what was estimated by the Δ R2* map in five regions.

Conclusion: These findings suggest that a quantitative susceptibility map is a promising technique for SvO₂ measurement. This method may be useful for quantitatively investigating oxygenation-dependent functional MRI studies. Magn Reson Med 77:592-602, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Keywords: hyperoxia; magnetic resonance imaging (MRI); quantitative susceptibility mapping (QSM); rat brain; venous oxygen saturation (SvO2).