Image Processing Reference
In-Depth Information
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FIGURE 11.16
The shape of the 1-D point-spread function for (a) symmetrical and
(b) asymmetrical k-space sampling. In the case of asymmetrical sampling, the PSF is
a complex function. The real part is depicted by the solid and the imaginary part by
the dotted line.
From the preceding expressions, it follows that symmetric sampling leads to
a real PSF, and asymmetric sampling to a complex PSF. Both situations are
depicted in Figure 11.16. In the case of a complex PSF, both real and imaginary
parts of the FIDs are mixed, and CSI spectra show the phase difference with
respect to each other. This may cause phasing problems. On the other hand, the
PSF shape corresponding to asymmetric sampling has a slightly improved profile
in terms of the diminished extent and amplitude of the side lobes.
In
Figure 11.17
the influence of the number of phase-encoding steps on PSF
shape is demonstrated. Clearly, PSF shape improves with the increasing number
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