Water diffusion and T₂ quantification in transient-state MRI: the effect of RF pulse sequence

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysical Measurement Techniques

Background:

• Water diffusion is a known confounder in quantitative T2 mapping.
• Transient-state techniques estimate T2 and T1 simultaneously, but are sensitive to diffusion-induced bias.
• Previous studies show conflicting results regarding the extent of diffusion-induced bias on T2 estimates.

Purpose of the Study:

• To investigate the effect of radiofrequency (RF) pulse angle sequences on diffusion-induced bias in T2 mapping.
• To determine the influence of RF pulse sequence parameters on the accuracy of T2 measurements.

Main Methods:

• Simulations and theoretical analysis were used to evaluate the impact of RF pulse sequences on T2 bias.
• The study focused on transient-state quantitative mapping techniques.
• Analysis considered realistic spoiling gradient areas for MRI.

Main Results:

• The specific transient-state RF pulse sequence significantly affects the level of diffusion-induced bias.
• The mean value of the RF pulse angles strongly influences the bias magnitude.
• Diffusion-induced bias is negligible in non-liquid human tissues but can be substantial (up to 15%) in phantoms for certain RF sequences.

Conclusions:

• RF pulse sequence design is critical for minimizing diffusion-induced bias in T2 mapping.
• Phantom studies require careful selection of RF sequences to ensure accurate T2 validation.
• The findings highlight the importance of accounting for RF sequence effects in quantitative MRI measurements.