On-resonance variable delay multipulse scheme for imaging of fast-exchanging protons and semisolid macromolecules

Area of Science:

• Magnetic Resonance Imaging
• Biophysical Chemistry
• Medical Physics

Background:

• Magnetization Transfer Contrast (MTC) and Chemical Exchange Saturation Transfer (CEST) are MRI techniques sensitive to molecular interactions.
• Existing methods face challenges in separating signals from different proton pools, especially fast-exchanging ones.

Purpose of the Study:

• To develop an on-resonance variable delay multipulse (VDMP) scheme.
• To image MTC and CEST contrast from total fast-exchanging protons (TFP) with exchange rates > 1 kHz.
• To separate and quantify MTC and CEST contributions based on varying proton transfer rates.

Main Methods:

• Applied a train of high-power binomial pulses at the water resonance.
• Varied the interpulse delay (mixing time) to analyze water signal reduction.
• Utilized variable mixing time to separate MTC and CEST signals from fast-exchanging protons.

Main Results:

• Phantom studies demonstrated successful separation of exchangeable protons (> 1 kHz) in various solutions and materials.
• Quantitative MTC and TFP maps of mouse brains showed distinct gray/white matter contrast for MTC protons.
• TFP maps were more uniform but slightly higher in gray matter.

Conclusions:

• The developed on-resonance VDMP method simplifies imaging of fast-exchanging protons and MTC components.
• This technique allows for the characterization of proton exchange dynamics in biological tissues.
• Offers a novel approach for quantitative MRI analysis of MTC and CEST effects.