Restriction-Weighted Q-Space Trajectory Imaging (ResQ): Toward Mapping Diffusion-Time Effects With Tensor-Valued...

Area of Science:

• Biomedical Imaging
• Diffusion MRI
• Cancer Research

Background:

• Tensor-valued diffusion encoding offers unique tissue microstructure sensitivity.
• Diffusion-time dependence can confound interpretation of diffusion MRI parameters.
• Understanding diffusion dynamics is crucial for cancer imaging.

Purpose of the Study:

• Introduce a novel framework, restriction-weighted q-space trajectory imaging (ResQ), to incorporate diffusion-time effects.
• Evaluate ResQ in a longitudinal study of prostate cancer xenografts.
• Improve the interpretability of diffusion MRI parameters by accounting for restriction and diffusion time.

Main Methods:

• Developed a novel gradient waveform design for tensor-valued encoding with controlled restriction weighting.
• Applied four waveforms on a 9.4T preclinical MRI system to prostate cancer xenografts.
• Introduced ResQ parameters: mean diffusivity (D), isotropic diffusional variance (V_Di), microscopic diffusion anisotropy (V_Da), and their diffusion-time dependence (ΔD, ΔV_Di, ΔV_Da).

Main Results:

• ResQ revealed clear diffusion-time dependence in all tumors, with significant longitudinal differences between treated and untreated groups.
• Key parameters showing differences included D, ΔD, and V_Di.
• Ignoring diffusion-time dependence in standard q-space trajectory imaging (QTI) led to substantial parameter bias, particularly overestimation of microscopic diffusion anisotropy.

Conclusions:

• Diffusion-time effects are significant in prostate cancer and must be considered in tensor-valued diffusion encoding.
• The ResQ framework provides controlled restriction weighting and enhanced interpretability of diffusion MRI parameters.
• ResQ may enable novel imaging biomarkers for disentangling diffusion properties and their time dependence in cancer.