On the sampling strategies and models for measuring diffusion exchange with a double diffusion encoding sequence.

Area of Science:

• Medical Imaging
• Biophysics
• Quantitative MRI

Background:

• Water exchange between biological compartments is crucial for understanding tissue function.
• Diffusion magnetic resonance imaging (dMRI) offers a non-invasive method to study this exchange.
• Existing dMRI models often rely on specific subsets of the double diffusion encoding (DDE) signal.

Purpose of the Study:

• To evaluate different sampling schemes within a general DDE signal representation for characterizing water exchange.
• To compare the performance of proposed sampling schemes against established models and their subsampling strategies.
• To assess the feasibility of using a general DDE signal with variable sampling for exchange measurements.

Main Methods:

• Employed a general representation of the DDE signal with constant b1, diagonal, and anti-diagonal sampling schemes.
• Proposed and compared a near-uniform sampling scheme against existing methods.
• Applied filter exchange and rapid exchange models with their respective subsampling schemes.
• Validated methods using both simulated and experimental data from a benchtop MR scanner.

Main Results:

• On synthetic data, diagonal and near-uniform sampling schemes provided estimates consistent with ground truth.
• On experimental data, shifted diagonal and near-uniform schemes yielded the most consistent results compared to full-space estimation.
• The proposed sampling schemes demonstrated robust performance in estimating water exchange.

Conclusions:

• Measuring water exchange using a general DDE signal representation with variable sampling schemes is feasible.
• Near-uniform and diagonal sampling strategies show promise for accurate exchange estimation in dMRI.
• Future work should focus on optimizing sampling schemes and incorporating additional biophysical properties into exchange models.