Accurate determination of brain metabolite concentrations using ERETIC as external reference

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Magnetic Resonance Spectroscopy (MRS) enables in vivo metabolite quantification using a reference signal.
• Human brain ¹H MRS commonly uses tissue water as a reference, but requires accurate water concentration estimation.
• ERETIC method offers an alternative by comparing metabolite signals to a phantom reference, correcting for coil loading.

Purpose of the Study:

• To enhance the accuracy of the ERETIC method by correcting for spatial B₁ inhomogeneities.
• To simplify ERETIC quantification through automatic phase correction.
• To validate the improved ERETIC method for in vivo metabolite concentration determination.

Main Methods:

• Implemented B₁ correction using volume-selective power optimization and contrast-minimized brain images.
• Corrected reception sensitivity variations by aligning phantom and in vivo voxel positions.
• Incorporated automatic phase correction for the ERETIC signal.

Main Results:

• Metabolite concentrations determined by the enhanced ERETIC method in 21 healthy subjects agreed with those derived using tissue water as a reference.
• Brain water concentrations measured with ERETIC correlated well with tissue segmentation and literature values.
• The B₁ correction scheme improved the accuracy of ERETIC-based metabolite quantification.

Conclusions:

• The refined ERETIC method provides accurate in vivo metabolite concentrations without assumptions about tissue water content.
• This technique offers potential advantages over internal water referencing, particularly for studying diseased brain tissues.
• The enhanced ERETIC method is a validated tool for reliable in vivo metabolite quantification.