Magnetization transfer phenomenon in the human brain at 7 T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Neuroimaging

Background:

• Magnetization transfer (MT) is crucial for MRI contrast, reflecting macromolecule and solute concentrations.
• MT effects are visualized via MTR images or quantified using the z-spectrum.

Purpose of the Study:

• To present methods for in vivo z-spectrum measurement and high-resolution MTR imaging at 7 T within SAR limits.
• To utilize a 3-compartment model for chemical exchange and MT parameter quantification from z-spectrum data.
• To investigate the potential of quantitative amide proton transfer (APT) imaging for myelination assessment.

Main Methods:

• Development of methods for in vivo z-spectrum measurement and high-resolution MTR imaging at 7 T.
• Application of a 3-compartment model to derive chemical exchange and MT parameters.
• Analysis of amide proton transfer (APT) effects and their variation across white matter structures.

Main Results:

• High-resolution MTR images and z-spectrum asymmetry maps were produced in vivo at 7 T.
• The amide proton transfer (APT) peak in the z-spectrum is more pronounced at 7 T compared to 3 T.
• Quantitative APT imaging revealed variations between the corpus callosum and other white matter, suggesting myelination-related differences.
• Chemical exchange was found not to be the cause of the grey-white matter phase shift in susceptibility weighted images.

Conclusions:

• The developed methods enable high-quality in vivo MT and z-spectrum analysis at 7 T.
• Quantitative APT imaging at 7 T is a promising tool for assessing myelination.
• Further research is needed to fully elucidate the role of chemical exchange in MRI contrast and susceptibility effects.