MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

• Published in: NeuroImage (Orlando, Fla.) Vol. 49; no. 2; pp. 1271 - 1281
• Main Authors: Marques, José P., Kober, Tobias, Krueger, Gunnar, van der Zwaag, Wietske, Van de Moortele, Pierre-François, Gruetter, Rolf
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.01.2010; Elsevier Limited
• Subjects: Acquisitions & mergers; Adult; Brain; Brain - physiology; Female; Humans; Magnetic Resonance Imaging - methods; Male; Phantoms, Imaging
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2009.10.002

The large spatial inhomogeneity in transmit B1 field (B1+) observable in human MR images at high static magnetic fields (B0) severely impairs image quality. To overcome this effect in brain T1-weighted images, the MPRAGE sequence was modified to generate two different images at different inversion times, MP2RAGE. By combining the two images in a novel fashion, it was possible to create T1-weigthed images where the result image was free of proton density contrast, T2⁎ contrast, reception bias field, and, to first order, transmit field inhomogeneity. MP2RAGE sequence parameters were optimized using Bloch equations to maximize contrast-to-noise ratio per unit of time between brain tissues and minimize the effect of B1+ variations through space. Images of high anatomical quality and excellent brain tissue differentiation suitable for applications such as segmentation and voxel-based morphometry were obtained at 3 and 7 T. From such T1-weighted images, acquired within 12 min, high-resolution 3D T1 maps were routinely calculated at 7 T with sub-millimeter voxel resolution (0.65–0.85 mm isotropic). T1 maps were validated in phantom experiments. In humans, the T1 values obtained at 7 T were 1.15±0.06 s for white matter (WM) and 1.92±0.16 s for grey matter (GM), in good agreement with literature values obtained at lower spatial resolution. At 3 T, where whole-brain acquisitions with 1 mm isotropic voxels were acquired in 8 min, the T1 values obtained (0.81±0.03 s for WM and 1.35±0.05 for GM) were once again found to be in very good agreement with values in the literature.