MP3RAGE: Simultaneous mapping of T₁ and in human brain at 7T

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Quantitative MRI

Background:

• Accurate mapping of T1 relaxation times and flip angles is crucial for quantitative MRI.
• Existing methods often require separate acquisitions or complex corrections, limiting efficiency and precision.
• MPRAGE sequences are widely used for anatomical imaging, but simultaneous quantitative mapping remains a challenge.

Purpose of the Study:

• To develop and validate a single MP3RAGE sequence for simultaneous mapping of T1 and local flip angles in the human brain.
• To achieve high-resolution (1 mm isotropic) whole-brain quantitative maps efficiently.
• To compare the novel MP3RAGE method against established T1 and flip angle mapping techniques.

Main Methods:

• A modified MP2RAGE sequence (MP3RAGE) incorporating a third RAGE acquisition with a higher flip angle was implemented.
• Closed-form solutions for T1 and flip angle were derived using curve fitting and rational approximation.
• The influence of k-space encoding and a saturation pulse on precision and artifact reduction was investigated.
• Validation was performed against inversion recovery for T1 and DREAM for flip angle mapping.

Main Results:

• Whole-brain T1 and flip angle maps were successfully acquired with MP3RAGE at 1 mm isotropic resolution in under 7 minutes.
• Optimized phase-encoding strategies and saturation pulses improved precision and reduced artifacts.
• MP3RAGE T1 and flip angle estimations showed good agreement with reference methods, with small deviations (+2.5 ± 3.1% for T1, -1.7 ± 8.6% for flip angle).

Conclusions:

• MP3RAGE enables simultaneous, analytical, and co-registered mapping of T1 and flip angles within a single, efficient MPRAGE acquisition.
• This technique effectively combines the benefits of MP2RAGE anatomical imaging with dual flip angle T1 mapping.
• The MP3RAGE method provides a robust and accurate approach for quantitative brain MRI at high resolution.