Can multi-slice information improve the conditioning of in-plane acceleration?

JosÃ© P. Marques^{1} and David G. Norris^{1}

Figure 2 shows examples of g-factor maps obtained for equivalent acceleration factors, using 2D or 3D GRAPPA and the implications of combining 3DGRAPPA with PE shifts. It is visible that the 3D GRAPPA does not provide any significant advantage (2nd column) if not combined with PE shifts (3rd and 4th column). While the benefits are minimal for Ry=3-4 , they increase significantly for 6 and 8 (Fig.3) with various fine resolution and contrast being preserved in the regions of greater g-noise amplification.

Figure 4 shows that some of the improvements seen in Fig. 2 and 3 were not translatable
into reduced aliasing and came at a price of a small degree of smoothing in the
z direction and much reduced detectability for 3Dxk_{y}z GRAPPA. ForR_{y}=8 the amount of power on successive slices was 5 and 20%
for the 3Dk_xk_{y}z and 3Dxk_{y}z GRAPPA respectively, while the power aliased was of 5, 7
and 16% for 2Dk_{x}k_{y}, 3Dk_{x}k_{y}z and 3Dxk_{y}z.

1. Breuer, F. A. et al. Controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) for multi-slice imaging. Magn. Reson. Med. 53, 684–691 (2005).

2. Cauley, S. F., Polimeni, J. R., Bhat, H., Wald, L. L. & Setsompop, K. Interslice leakage artifact reduction technique for simultaneous multislice acquisitions. Magn. Reson. Med. 72, 93–102 (2014).

3. Breuer, F. A. et al. Controlled aliasing in volumetric parallel imaging (2D CAIPIRINHA). Magn. Reson. Med. 55, 549–556 (2006).

4. Narsude, M., Gallichan, D., van der Zwaag, W., Gruetter, R. & Marques, J. P. Three-dimensional echo planar imaging with controlled aliasing: A sequence for high temporal resolution functional MRI. Magn. Reson. Med. n/a–n/a (2015). doi:10.1002/mrm.25835

5. Zahneisen, B., Poser, B. A., Ernst, T. & Stenger, V. A. Three-dimensional Fourier Encoding of Simultaneously Excited Slices: Generalized Acquisition and Reconstruction Framework. Magn. Reson. Med. Off. J. Soc. Magn. Reson. Med. Soc. Magn. Reson. Med. 71, 2071–2081 (2014). 9. Robson, P. M. et al. Comprehensive Quantification of Signal-to-Noise Ratio and g-Factor for Image-Based and k-Space-Based Parallel Imaging Reconstructions. Magn. Reson. Med. Off. J. Soc. Magn. Reson. Med. Soc. Magn. Reson. Med. 60, 895–907 (2008).

Slice specific 3D kernels used on the 3D GRAPPA reconstruction for an
in-plane acceleration Ry=3 and phase encoding shifts of 0, 1 and 2
on the left, centre and right panel respectively. Light gray and dark grey
pixels represent source and target GRAPPA points.

g-factor maps for different in-plane
accelerations (rows) using 2D grappa left column, vs. 3D GRAPPA with different
integer phase encoding shifts of 0, ~1/3Ry and ~Ry/2 (values given inside the
image). Note that the colorbar ranges are different for different acceleration factors.

Two exemplar
slices covering deep gray matter structures (white arrow) and cerebellar
folding (black arrow) reconstructed with different GRAPPA implementations
(columns) for increasing acceleration and varying PE shifts (rows).

Top panel shows 4
synthetic timecourses added to the raw data in one slice only. The three
different columns refer to different reconstruction strategies of same dataset
$$$R_y=8$$$ and PE shift 3. The rows show the mean image reconstructed for the
same three slices and the $$$\beta$$$ maps associated with each of the
timecourses. Arrows point regions affected by aliasing and smoothing.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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