Limits to flow detection in phase contrast MRI.

Area of Science:

• Magnetic Resonance Imaging
• Biophysics
• Fluid Dynamics

Background:

• Pulsed gradient spin echo (PGSE) signal behavior is complex in slow flow.
• Displacements from flow comparable to diffusion alter signal characteristics.

Purpose of the Study:

• To investigate PGSE signal behavior in the slow-flow regime.
• To determine optimal parameters for phase contrast velocimetry in porous media.
• To validate theoretical models with MRI experiments.

Main Methods:

• Theoretical modeling of PGSE signal attenuation.
• Development of phase contrast velocimetry protocols for slow flow.
• PGSE echo planar imaging experiments on water flow in bulk and beadpack regions.

Main Results:

• PGSE signal is dominated by attenuation, not oscillation, in slow flow.
• Optimal PGSE parameter 'q' depends on diffusive length scale, not velocity encoding.
• Minimum detectable mean velocity is on the order of μm/s.
• Velocities as low as 6 μm/s were successfully detected.

Conclusions:

• The study provides a theoretical framework for slow-flow velocimetry using PGSE.
• MRI protocols and validation bridge the gap between porous media NMR and clinical MRI.
• This work enables precise velocity measurements in complex biological and pre-clinical systems.