Quantitative Diffusion and T2 Mapping Using RF-Modulated Phase-Based Gradient Echo Imaging

Area of Science:

• Magnetic Resonance Imaging
• Quantitative Imaging
• Biomedical Engineering

Background:

• Conventional diffusion-weighted imaging (DWI) suffers from geometric distortions.
• Quantitative diffusion and T2 mapping are crucial for accurate tissue characterization.
• There is a need for advanced MRI techniques to overcome limitations of current methods.

Purpose of the Study:

• To introduce and evaluate a novel RF-phase modulated gradient echo (GRE) method for quantitative diffusion MRI.
• To assess the feasibility of this method for high-resolution 3D quantitative diffusion/T2 mapping.
• To mitigate geometric distortion and serve as an alternative to conventional DWI.

Main Methods:

• Developed a phase-based diffusion (PBD) method using RF phase modulation to encode diffusion and T2 information.
• Employed a closed-form analytical model for joint apparent diffusion coefficient (ADC) and T2 mapping via iterative reconstruction.
• Evaluated feasibility through Bloch equation simulations, phantom experiments, and in vivo imaging.

Main Results:

• Simulations showed PBD provides more accurate median ADC estimates at low SNRs compared to SS-EPI.
• Phantom studies demonstrated good agreement for PBD-derived ADC (R²=0.99) and strong correlation for T2 (R²=0.89).
• In vivo imaging of prostate disease showed high-resolution ADC and T2 maps with minimal geometric distortions.

Conclusions:

• PBD offers improved geometric fidelity for ADC and T2 maps in phantoms and in vivo.
• The method provides robust median ADC estimates from noisy data, as shown by simulations.
• PBD is promising for high-resolution DWI applications, particularly in prostate MRI.