Hi Vince,
It seems that 2dImReg is designed to handle only time series
input. It may be a bit of a hack, but for now you could use
3dTcat to put this.brain+orig into a 2 volume time series:
3dTcat -prefix this2 this.brain+orig this.brain+orig
Then use "-input this2+orig" in your 2dImReg command.
You can rip out "this.brain.2dreg+orig[0]' when that is done.
Yes, it's a hack. But at least you can do it right now. :)
- rick