Combining ³¹P-¹H Cross Polarization With Magnetization Transfer: A Novel Approach for Myelin Investigation.

Area of Science:

• Neuroimaging
• Biophysics
• Materials Science

Background:

• White matter integrity is crucial for neurological function, with myelin damage a hallmark of diseases like multiple sclerosis.
• Current MRI relies on hydrogen-1 (¹H) for contrast, limiting specificity in myelin assessment.
• Phosphorus-31 (³¹P) is abundant in myelin phospholipids and sensitive to structural and dynamic changes.

Purpose of the Study:

• To develop and demonstrate MRI-compatible probes for myelin using ³¹P.
• To compare solid-state NMR techniques (cross-polarization vs. single pulse excitation) for ³¹P detection in white matter.
• To investigate magnetization transfer (MT) combined with cross-polarization (CP) for probing myelin-water interactions.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) techniques, including cross-polarization (CP) and single pulse excitation.
• Magnetization transfer (MT) experiments combined with CP to detect polarization exchange.
• Pulsed magnetic field gradients to isolate and detect signals from myelin ³¹P transferred to aqueous ¹H.

Main Results:

• ¹H-³¹P CP spectra retained myelin-specific ³¹P patterns, unlike aqueous ³¹P signals.
• Observed bi-directional polarization exchange between myelin ³¹P and water via a distinct ¹H pool.
• Successfully isolated a small but informative signal of transferred magnetization from myelin ³¹P to aqueous ¹H.

Conclusions:

• ³¹P-based MRI offers a novel, sensitive probe for myelin structure and dynamics, distinct from conventional ¹H MRI.
• This two-step polarization transfer method provides access to membrane/water interface information previously unavailable.
• The technique holds significant potential for early detection, monitoring, and understanding of white matter diseases and injuries.