Quantification of complex flow using MR phase imaging--a study of parameters influencing the phase/velocity relation

Area of Science:

• Medical Imaging
• Fluid Dynamics
• Biophysics

Background:

• Magnetic Resonance Imaging (MRI) phase mapping is a technique used to visualize and quantify blood flow.
• Understanding the behavior of phase shifts in complex flow is crucial for accurate quantification.

Purpose of the Study:

• To investigate the impact of flow models and imaging parameters on motion-induced phase angle in MR flow phase mapping.
• To determine the linearity of the phase/velocity relationship in healthy and stenotic vessel phantoms under varying flow conditions.

Main Methods:

• Utilized a phantom with straight and constricted tubes to simulate healthy and stenotic vessels.
• Maintained nonpulsatile flow (0-1 m/sec) and studied phase/velocity relations under complex flow conditions.
• Investigated the influence of pulse sequence parameters (velocity encoding, voxel size) on the phase/velocity relation.

Main Results:

• Nonlinearity in the phase/velocity relation was observed in post-stenotic areas with separated flow due to dephasing effects.
• No breakdown in linearity was found in regions with fully developed turbulent flow in straight tubes.
• First- and second-order velocity encoding and voxel size significantly influenced the phase/velocity relation.

Conclusions:

• MR phase mapping can quantitatively measure flow in complex flow regions, including those with flow separation.
• The technique shows promise for future clinical applications, particularly in studying conditions like valvular heart disease.