Quantification of slow flow using FAIR

Area of Science:

• Medical Imaging
• Fluid Dynamics
• Biophysics

Background:

• Phase contrast (PC)-based MRI is accurate for flow quantification but struggles with very slow velocities due to long echo times and strong gradients.
• Alternative methods using time-of-flight or inflow effects offer shorter echo times and no flow-encoding gradients.

Purpose of the Study:

• To present and validate a new magnetic resonance imaging (MRI) method for imaging and quantifying very slow fluid flow velocities (around 0.1 mm/s).
• To provide a viable alternative to PC-MRI for slow flow quantification, particularly in fluids with short T2 relaxation times.

Main Methods:

• Utilized magnetization preparation with alternating slice-selective and nonselective inversion pulses (flow-sensitive alternating inversion recovery - FAIR).
• Employed a fast gradient-echo detection sequence to measure the apparent spin-lattice relaxation rate (R(1)*) of the flowing fluid.
• Validated the method for slow flow quantification at low Reynolds numbers.

Main Results:

• Successfully imaged and quantified fluid flow at velocities as low as 0.1 mm/s.
• Demonstrated the method's effectiveness in fluids with short T2 values, where PC-MRI is less sensitive.
• Established R(1)* measurement as a viable approach for slow flow quantification.

Conclusions:

• The presented FAIR-based R(1)* measurement technique is suitable for quantitative imaging of slow flow (0.1 mm/s) at low Reynolds numbers.
• This method offers an advantage over PC-MRI for slow flow quantification in fluids with short T2 values.
• The technique expands the capabilities of MRI for precise flow measurement in challenging fluid environments.