Master's Thesis - Studierstube Augmented Reality Project - Graz ...

3.5 Cine Cardiac Fast Low-Angle Shot with Parallel-Imaging Technique
Figure 3.14: Computing the complex difference of a flow compensated and flow sensitive
signal produces a complex difference vector for moving signals and zero for stationary
spin signals. The image implies that one of the major defiances is the 2π-periodicity
of a complex signal. The phase shift has to be mapped precisely between −π and π
which means that the maximum expected velocity has to be known in advance.
artifacts may occur from time to time because v enc has to be defined empirically. On
the other hand a v enc value defined too high will result in a low contrast velocity coding
image. That is one of the reasons some further post processing steps are required or
the usage of a sequence with pre-measured v enc . Since sequences with automatically
estimated v enc were experimental during writing this thesis, further data post processing
steps are described in section 4.2 due to empirical defined v enc -values. Figure 3.15 shows
examples for v(x ijk ) > v enc and v enc