Parallel MRI: Concepts and Methods - Advance Image Processing in Magnetic Resonance Imaging - page 78

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FIGURE 3.18 Axial neurological image acquired using irregular sub-sampling strategy.

approximately 20 sec. This breath hold is certainly possible with a healthy
volunteer, but very taxing on patients with cardiac disease. Using parallel imag-
ing to increase the acquisition rate decreases the breath-hold time by the accel-
eration factor. Thus, with 2x- and 4x-acceleration, the breath-hold time reduces
to approximately 11 sec and 6 sec, respectively.
If used to improve spatial resolution, parallel imaging provides an improve-
ment proportional to the acceleration factor. Figure 3.18 shows a demonstration
of this with an axial image of the brain. The image was acquired using four coils
at 4x-acceleration. The acquired data were subsampled using a set of k-space
lines whose density mirrors the Fourier signal energy distribution. This distribu-
tion is shown in Figure 3.18(a), with the corresponding sampling pattern is shown
Figure 3.18(b). The resulting image reconstructed using SPACE RIP is shown in
Figure 3.18(c).

3.5 SUMMARY

This chapter presented a basic overview of the current state of the art in parallel
MR image reconstruction techniques. Starting from the signal acquisition model,
we reviewed the reconstruction approach given by SMASH, its subsequent improve-
ments leading to GRAPPA, SENSE, and SPACE RIP. A number of reconstruction
examples were given to illustrate the effectiveness of each method and a few of the
differences between them.

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2. Hutchinson, M. and Raff, U. (1998). Fast MRI data acquisition using multiple

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3. Kwiat, D., Einav, S., and Navon, G. (1991). A decoupled coil detector array for

fast image acquisition in magnetic resonance imaging. Med. Phys. 18(2): 251-265.