Flow properties of fast three-dimensional sequences for MR angiography

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Imaging Physics

Background:

• Reducing scan time is crucial for time-of-flight (TOF) and phase contrast angiography (PCA) MRI sequences.
• Optimizing three-dimensional (3D) k-space trajectories is key to achieving faster imaging.
• The choice of trajectory impacts scan time, resolution, and sensitivity to flow and motion.

Purpose of the Study:

• To present a formalism for comparing flow/motion sensitivity of 3D MRI trajectories.
• To evaluate and compare the flow/motion properties of various 3D k-space trajectories.
• To guide the selection of optimal trajectories for angiography applications.

Main Methods:

• Developed a formalism based on velocity k-space behavior to compare trajectory sensitivity.
• Determined velocity k-space position as a function of spatial k-space position.
• Compared trajectories using velocity k-space maps, simulations, and a computed index.

Main Results:

• Evaluated flow/motion properties of 3D trajectories including cones, spiral-pr hybrid, spherical stack of spirals, 3DFT, 3D echo-planar, and shells.
• The cones trajectory demonstrated superior flow/motion sensitivity.
• The stack of spirals trajectory offered enhanced geometric flexibility, albeit with increased flow sensitivity.

Conclusions:

• The cones trajectory is optimal for flow/motion sensitivity but limited in geometric flexibility for anisotropic resolutions.
• The stack of spirals trajectory provides a valuable alternative when geometric flexibility is prioritized over absolute minimal flow sensitivity.
• This comparative framework aids in selecting appropriate 3D trajectories for advanced angiography MRI.