Aims and objectives
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...
Methods and materials
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...
Results
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...
Conclusion
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.
References
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