Flow-compensated intravoxel incoherent motion diffusion imaging.

Area of Science:

• Medical Imaging
• Biophysics
• Diffusion MRI

Background:

• Intravoxel incoherent motion (IVIM) imaging is crucial for assessing tissue microdynamics.
• Accurate estimation of the pseudo-diffusion coefficient (D*) in IVIM is challenging.
• The commonly assumed biexponential model may not fully capture complex IVIM signal behavior.

Purpose of the Study:

• To evaluate the validity of the biexponential limit in IVIM imaging.
• To determine the pseudo-diffusion coefficient (D*), characteristic timescale (τ), and velocity (v) of incoherent motion.
• To investigate the utility of flow-compensated diffusion gradients in IVIM analysis.

Main Methods:

• Incorporation of bipolar and flow-compensated diffusion gradients into a single-shot EPI sequence.
• Acquisition of imaging data from a flow phantom and healthy volunteers.
• Development of a formalism based on normalized phase distributions for IVIM signal calculation beyond the biexponential limit.

Main Results:

• Flow-compensated gradients demonstrated reduced signal attenuation compared to bipolar gradients.
• A signal dependence on flow-compensated gradient duration was observed at low b-values in volunteers.
• Estimated IVIM parameters: Liver (v=4.60±0.34 mm/s, τ=144±10 ms), Pancreas (v=3.91±0.54 mm/s, τ=224±47 ms).

Conclusions:

• The biexponential limit inadequately models diffusion signals in liver and pancreas.
• Flow-compensated and bipolar diffusion gradients of varying durations enable determination of IVIM motion characteristics.
• This approach enhances the accuracy of IVIM parameter estimation for tissue characterization.