Improving -inhomogeneity tolerance by resolving non-bijection in MP2RAGE R₁ mapping: A 2D look-up table approach...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Quantitative MRI

Background:

• Magnetization-prepared 2 rapid gradient echo (MP2RAGE) imaging can exhibit non-bijective mapping, leading to ambiguities, especially when optimized for higher B1-inhomogeneity tolerance.
• Deriving a second contrast from MP2RAGE magnitude images allows for the resolution of these ambiguities.

Purpose of the Study:

• To verify that non-bijective mapping in MP2RAGE can be resolved using a two-dimensional look-up table approach.
• To demonstrate that the expanded parameter space improves B1-inhomogeneity tolerance without additional prerequisites.

Main Methods:

• MP2RAGE images were acquired at 3 Tesla using standard and B1-inhomogeneity-optimized parameters in 3 subjects.
• B1-inhomogeneity tolerance was assessed via excitation-pulse amplitude scalings across multiple sessions.

Main Results:

• R1 maps derived from B1-optimized protocols showed significantly reduced B1-inhomogeneity effects without increasing scan time.
• Successful derivation of these R1 maps was dependent on the two-dimensional look-up table approach.

Conclusions:

• MP2RAGE sequence parameters can be optimized for B1-inhomogeneity tolerance while enabling accurate R1 mapping via a 2D look-up table.
• This approach eliminates the need for an additional B1 map.
• The expanded parameter space offers potential for optimizing scan times, signal-to-noise ratio, and contrast-to-noise ratio.