Global cerebrospinal fluid as a zero-reference regularization for brain quantitative susceptibility mapping.

Area of Science:

• Neuroimaging
• Medical Physics
• Biomedical Engineering

Background:

• Quantitative susceptibility mapping (QSM) is a valuable MRI technique for visualizing brain structures.
• Accurate zero referencing is crucial for reliable QSM measurements.
• Current methods often rely on limited regions like the ventricles, potentially introducing artifacts.

Purpose of the Study:

• To develop and validate a global cerebrospinal fluid (CSF) method for automated and consistent zero referencing in brain QSM.
• To compare the performance of the global CSF method against traditional ventricular CSF regularization.

Main Methods:

• Whole brain CSF masks were automatically segmented using gradient echo transverse relaxation ($$) maps.
• Regularization was applied to ensure uniform susceptibility within the CSF volume during field-to-susceptibility inversion.
• The global CSF method was compared to ventricular CSF regularization in healthy subjects (n=12) and patients with multiple sclerosis (MS) and Parkinson's disease (PD) (n=17 and n=10, respectively).

Main Results:

• Global CSF regularization demonstrated higher repeatability and consistency in QSM measurements compared to ventricular CSF regularization.
• The global method exhibited a smaller bias (-0.13 ppb vs. -2.7 ppb) and narrower limits of agreement.
• In PD and MS patients, global CSF regularization reduced shadow artifacts and significantly improved QSM image quality scores.

Conclusions:

• The proposed whole brain CSF method provides a more robust and accurate approach for QSM zero referencing.
• This technique enhances the repeatability and image quality of brain QSM.
• The global CSF method is a significant improvement over the ventricular CSF method for clinical applications.