Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Medical Physics

Background:

• High-field MRI (7 T and above) faces challenges with radiofrequency (RF) B1 inhomogeneities affecting T1-weighted brain imaging.
• The established MP2RAGE sequence addresses these inhomogeneities but isn't universally accessible on all MRI systems.

Purpose of the Study:

• To implement and evaluate a sequential protocol for obtaining normalized Magnetization Prepared Rapid Gradient Echo (MPRAGE) images.
• To provide a viable alternative to MP2RAGE for high-quality, normalized T1-weighted brain imaging, particularly when MP2RAGE is unavailable.

Main Methods:

• Developed a sequential protocol to acquire normalized MPRAGE images at ultra-high resolutions (0.7-0.9 mm isotropic).
• Optimized a reference gradient-recalled echo (GRE) sequence for MPRAGE normalization, balancing white-gray matter contrast and signal-to-noise ratio (SNR).
• Reduced scan time by increasing the reference voxel size (8x) and used a separately acquired flip angle map for bias correction.

Main Results:

• Achieved significant reduction in intra-subject coefficient-of-variation (CV) in white matter (WM) from 20% to 7.9% after normalization.
• Demonstrated reduced inter-subject CV in WM from 13% to 7.6% post-normalization, indicating improved consistency.
• T1 maps derived from forward signal modeling showed no significant bias after correction.

Conclusions:

• A non-interleaved acquisition for normalizing MPRAGE provides a simple and effective alternative to MP2RAGE.
• This method enables the generation of semi-quantitative, purely T1-weighted images convertible to T1 maps.
• Increasing reference voxel size effectively reduces scan time with minimal impact on image quality.