Macromolecular proton fraction mapping based on spin-lock magnetic resonance imaging

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Diagnostics

Background:

• Macromolecular proton fraction (MPF) is a crucial parameter in Magnetization Transfer (MT) MRI, reflecting the proportion of immobile protons in macromolecules.
• Existing MPF-mapping methods have limitations that necessitate more robust quantification techniques.

Purpose of the Study:

• To develop and validate a novel method for quantifying MPF using spin-lock MRI, termed MPF quantification based on spin-lock (MPF-SL).
• To explore the advantages of MPF-SL over current MPF-mapping techniques.

Main Methods:

• MPF-SL utilizes off-resonance spin-lock to specifically measure the MT effect, isolating it from other relaxation processes.
• A theoretical framework allows MPF quantification from the measured relaxation rate (Rmpfsl) without requiring prior tissue relaxation parameters (T1, T2).
• Validation was performed using Bloch-McConnell simulations, phantom studies, and in vivo 3.0T liver imaging.

Main Results:

• MPF-SL demonstrated robustness, showing insensitivity to variations in mobile water and chemical exchange pools in simulations and phantom experiments.
• The method proved specific to the MT effect, enabling reliable MPF measurement.
• In vivo liver studies successfully utilized MPF-SL to detect collagen deposition associated with liver fibrosis.

Conclusions:

• MPF-SL is a novel, spin-lock MRI-based method for MPF quantification that effectively removes confounding factors.
• The specificity and reliability of MPF-SL make it a promising tool for MPF-sensitive diagnostic imaging in clinical applications.