Phase unwrapping
- The conventional path-based methods in the spatial domain
- the linear fitting methods in the temporal domain
Its limitation
- The difficulty of phase unwrapping can be descended by the low SNR.
Background phase removal
- Its goal is the separation of the background phase from phase contributed by brain tissue itself.
- It is commonly used in SWI by homodyne filtering, traditional high-pass filtering.
- this filtering can remove a substantial portion of low frequency components of the tissue phase along with the background phase.
Its limitation
- this will lead to inaccurate quantification of susceptibility.
Advanced techniques
- SHARP (the sophisticated harmonic artifact reduction for phase data)
- PDF (the projection onto dipole fields)
- HARPERELLA (harmonic phase removal using the Laplacian operator) - it achieves phase unwrapping and background removal simultaneously