Free-Breathing Hepatic Oxygen Extraction Fraction (OEF) Mapping Using Radial GESSE

Area of Science:

• Medical Imaging
• Biophysics
• Hepatology

Background:

• Noninvasive assessment of hepatic oxygenation is crucial for diagnosing and monitoring liver pathologies.
• Current methods for liver oxygenation assessment are limited by single-slice acquisitions and require breath-holding, hindering comprehensive evaluation.
• Developing motion-robust, whole-liver techniques is essential for accurate hepatic oxygenation monitoring.

Purpose of the Study:

• To develop and evaluate a motion-robust technique for whole-liver oxygen extraction fraction (OEF) mapping.
• To utilize a radial gradient-echo sampling of spin-echo (rGESSE) sequence combined with an artificial neural network (ANN) for OEF quantification.
• To enable noninvasive, volumetric assessment of hepatic oxygenation under free-breathing conditions.

Main Methods:

• A multi-slice rGESSE sequence with radial sampling was employed on a 1.5T MRI system in seven healthy volunteers under free-breathing.
• Signal processing involved bias-field correction and 3D median filtering.
• OEF, deoxygenated blood volume (DBV), and transverse relaxation rate (R2) were estimated using a trained feedforward ANN based on simulated quantitative blood oxygen-level-dependent (qBOLD) signal models.

Main Results:

• Whole-liver OEF maps were successfully generated in all volunteers during free-breathing, demonstrating consistent spatial patterns.
• The mean hepatic OEF was 55.75% ± 6.88%, and the mean DBV was 0.568 ± 0.039.
• ANN-based fitting showed superior stability and artifact suppression compared to standard least-squares regression, despite a systematic overestimation of OEF compared to literature values.

Conclusions:

• The study successfully demonstrated the feasibility of free-breathing, whole-liver OEF mapping using rGESSE and ANN analysis.
• This approach offers improved motion robustness for noninvasive hepatic oxygenation assessment.
• The technique holds potential for clinical applications in the diagnosis and monitoring of liver diseases.