Noninvasive quantification of renal venous oxygenation with field-insensitive T₂ preparation and fast acquisition

The development of a reliable MRI technique to quantify renal oxygen extraction fraction and metabolism can help in the evaluation of tissue hypoxia in kidney diseases. This study aims to develop a field inhomogeneity-insensitive and motion-robust method for noninvasive renal oxygenation quantification.

A new sequence using adiabatic T₂ preparation (B₁-insensitive-rotation-n) with Fourier transform-based velocity-selective saturation and echo-planar imaging readout was proposed, referred to as TRUFIFA (T₂ relaxation under field-insensitive preparation and fast acquisition). We first demonstrated a robust T₂ quantification at different B₀ and B₁ offsets through simulation and phantom studies. Then, the sequence parameters were optimized in vivo with considerations of signal-to-noise ratio and contrast-to-noise ratio. The performance of the new sequence was shown using the comparison between B₁-insensitive-rotation-n and MLEV T₂ preparation. Finally, the test-retest reproducibility of the new method was examined.

Simulation and phantom studies demonstrated a robust T₂ quantification at different B₀ and B₁ offsets. Optimized free-breathing TRUFIFA yielded an averaged Y_v of 87.5 ± 2.6%, the feasibility of which in vivo was further shown by a positive correlation between venous T₂ and blood flow (R² = 0.33). An excellent reproducibility was found with a coefficient of variation of intrasession (T₂: 1.79 ± 0.88%, Y_v: 0.88 ± 0.48%) and intersession (T₂: 3.81 ± 2.23%, Y_v: 1.81 ± 0.94%).

A new method for quantification of renal oxygenation with inhomogeneity-insensitive T₂ preparation and fast acquisition was developed, which has the potential for clinical applications.