fScan Reference Manual, Chapter 2 (CmdLineOptions:Expr): Roimask
usage: -expr roimask [ROINUM [NROIS]]
Only keep region within selected Block ROI's. If multiple Block ROI's are associated with the current data set, all will be kept by default. Or you can select just a subset of the active ROI's by specifying ROINUM (how many to skip) and/or NROIS (how many to use).