If you are going to use 3dDeconvolve, it is better to remove the undesired components with that program, during the analysis, by using the
-stim_base option, rather than using 3dDetrend. The reasons for this are explained in Doug Ward's manual for 3dDeconvolve. 3dDetrend is really intended for use when you are going to do something special to the data, outside the realm of linear regression.
bob cox