Quantitative macromolecular proton fraction imaging using pulsed spin-lock

Area of Science:

• Magnetic Resonance Imaging
• Quantitative Imaging

Background:

• Quantitative magnetization transfer (MT) imaging simplifies macromolecular proton fraction (MPF) quantification by removing dependency on water pool parameters and T1 maps.
• Current spin-lock MRI methods for MPF quantification are limited by long radiofrequency (RF) pulse durations, constrained by hardware and specific absorption rate (SAR) limits.

Purpose of the Study:

• To develop a novel method, MPF mapping using pulsed spin-lock (MPF-PSL), to overcome limitations of existing spin-lock MRI techniques for quantitative MT imaging.
• To enable extended spin-lock durations within hardware and SAR safety limits for improved MPF quantification.

Main Methods:

• MPF-PSL utilizes a pulsed spin-lock train with intermittent free precession periods to achieve extended total spin-lock durations.
• An analytical framework was developed to model magnetization dynamics, ensuring MT-specific quantification and minimizing water pool confounding effects.
• The method was validated using Bloch-McConnell simulations, phantom studies, and in vivo 3T MRI.

Main Results:

• Simulations and phantom studies confirmed MPF-PSL's insensitivity to water pool parameters and robust MPF quantification.
• In vivo studies demonstrated the clinical utility of MPF-PSL for detecting collagen deposition in liver fibrosis patients.

Conclusions:

• MPF-PSL offers a practical and effective solution for quantitative MT imaging.
• The method shows significant potential for widespread clinical applications, particularly in assessing tissue fibrosis.