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

PURPOSE: To introduce and evaluate the feasibility of a novel RF-phase modulated gradient echo (GRE) method for quantitative diffusion MRI, aimed at mitigating geometric distortion and enabling high-resolution 3D quantitative diffusion/T2 mapping as a complementary alternative to conventional DWI.

THEORY AND

METHODS

The proposed phase-based diffusion (PBD) method employs RF phase modulation to encode both diffusion and T2 information into the GRE signal phase. A closed-form analytical model enables joint apparent diffusion coefficient (ADC) and T2 mapping via iterative reconstruction. The method's feasibility was evaluated via Bloch equation simulations, phantom experiments, and preliminary in vivo imaging studies.

RESULTS

Monte Carlo simulations revealed that PBD provides more accurate median ADC estimates at low signal-to-noise ratios (SNRs) compared to conventional single-shot echo-planar imaging (SS-EPI), although PBD exhibited greater variability. Phantom studies demonstrated good agreement for PBD-derived ADC values (e.g., R2 = 0.99) with reference methods and strong correlation for PBD-derived T2 values (e.g., R2 = 0.89), though the latter showed some systematic bias in phantoms. In vivo results from patients with benign or malignant prostate disease demonstrated the feasibility of the PBD method to provide high-resolution ADC and T2 maps with minimal geometric distortions relative to conventional SS-EPI.

CONCLUSION

PBD provides ADC and T2 maps with improved geometric fidelity in phantoms and in vivo, and offers robust median ADC estimates from noisy data based on simulations. This combination of spatial precision and noise characteristics makes PBD promising for applications such as high-resolution DWI for prostate MRI.