Quantitative MRI at Ultra-High Field (UHF) hold promise to investigate Alzheimerr's Disease (AD), which is characterized by an alteration of iron concentration. T2*-weighted images and the effective transverse relaxation rate (R2*) have been shown to be highly sensitive to B0 in-homogeneities generated by iron concentration (Langkammer et al., 2010; Stüber et al., 2014). However, B0 fluctuation induced by the increase in susceptibility-induced-field variations at UHF, can heavily degradate image quality by introducing artifacts such as ghosting and blurring. In this study we present a substantial...

Four patients with Alzheimer’s Disease (AD) were scanned at 9.4T using a multi-echo (N=6) 3D-GRE sequence (0.375x0.375x0.8mm3voxel size, TR=42ms; TE=6 to 30ms in steps of 6ms, TA=9min, FOV=192x174x70.4mm3, matrix size=512x464x88). An FID navigator was acquired before the phase-encoding and readout pre-winding gradients, with no gradients applied in the readout direction during the acquisition of the navigator. For each phase-encoding step the navigator was then used to recover the phase offset, which was successively subtracted from the corresponding k-space data in a corresponding echo. The phases...

Figure 1 shows T2*-weighted images of a representative AD patients, AD06. The top row shows the images reconstructed with navigator correction. The bottom row shows the same slices of the images reconstructed without navigator correction. A substantial reduction of the artifacts (including blurring and ghosting artifacts) after navigator echo correction is clearly evident (e.g. in Putamen and Caudate nucleus), as evidenced by the zoomed images. Figure 2 shows R2* mapping of the same patients, using T2* images reconstructed with navigator (top row) and without navigator...

T2* weighted images and R2* maps provide a potential means for investigating Alzheimer’s Disease, by detecting small signal changes due to the variation of iron concentration. Although a higher SNR can be achieved at ultra high field, challenges arise from the greater inhomogeneity of B0 field. In this study we showed that the quality of the T2*-weighted images and R2* maps were substantially inproved by using the navigator echoes approach, even in areas with strong magnetic field inhomogeneity.

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