The arterial spin labeling module quickly and simply produces a difference time series, an average of the difference series, and a scaled version of the average difference (CBF). Clicking on the module produces these image volumes automatically using the default settings. Action buttons perform:
- Calculator button: Generate the difference time series, the average of the difference series, and CBF after changing any of the options in the side panel.
- Run button: Convert the time series to a difference series, overwriting the original time series in program memory.
- Save button: Write the difference time series, the average difference, and CBF to files with names “diff”, “av-diff”, and “CBF” in the respective input directories.
Quantification of CBF uses the method described in
Magnetic Resonance in Medicine 2015; 73:102–116. Recommended Implementation of Arterial Spin-Labeled Perfusion MRI for Clinical Applications: A Consensus of the ISMRM Perfusion Study Group and the European Consortium for ASL in Dementia.
Parameters are mostly self-explanatory, Note that the average difference image uses the selection of volumes shows on the top right, which by default excludes the first two volumes to avoid non-steady-state artifact.
ASL generally benefits from robust smoothing. This is built into the ASL module directly, so one does not need to rely upon the dedicated smoothing module for this.
Subtraction can use the pair-wise approach or the symmetric difference method, which is preferable for rapid transitions.