Relaxation-Compensated Chemical Exchange Saturation Transfer MRI in the Brain at 7T: Application in...

Area of Science:

• Neuroimaging
• Biochemistry
• Neurology

Background:

• Chemical exchange saturation transfer (CEST) MRI offers high-resolution, sensitive biochemical analysis in vivo without contrast agents.
• Ultrahigh field strength (7.0 T) enhances CEST MRI's spectral resolution and sensitivity for metabolites like glutamate, a key neurotransmitter.
• Previous studies indicate altered glutamate regulation in multiple sclerosis (MS), necessitating advanced imaging techniques for investigation.

Purpose of the Study:

• To investigate glutamate levels in MS patients using advanced CEST MRI techniques.
• To isolate glutamate-specific CEST signals by correcting for confounding factors like magnetization transfer (MT) and T1 relaxation.
• To explore the relationship between glutamate-weighted CEST signals and cognitive function in MS.

Main Methods:

• Acquisition of glutamate-weighted CEST data at 7.0 T in 20 relapsing-remitting MS patients and healthy controls.
• Application of Lorentzian fitting to remove asymmetric MT contributions and AREX correction using R1 maps to isolate glutamate signals.
• Correlation analysis between AREX values and cognitive function assessed by the Minimal Assessment of Cognitive Function in MS battery.

Main Results:

• Glutamate-weighted AREX contrast was higher in gray matter than white matter, with reduced tissue differences after corrections.
• No significant difference in AREX was observed in normal-appearing gray and white matter between MS patients and controls.
• Significantly elevated glutamate-weighted AREX was found in white matter lesions of MS patients, correlating with disability and cognitive function.

Conclusions:

• MT and AREX corrections are crucial for accurately characterizing glutamate-weighted CEST signals in MS.
• Elevated glutamate in MS white matter lesions suggests a role in disease pathology.
• Further research with larger cohorts is needed to confirm the correlation between glutamate levels, disability, and cognitive impairment in MS.