As I understood what a 3 phase bone scan will do is to look at the effects CRPS is having on the bones. Since CRPS can cause osteopenia due to reduced blood flow & neurogenic edema and osteoporosis from disuse, reduced weight bearing and nutritional deficits from the affects it plays on our GI tract etc.

Thermography (I think) is what looks for blood pooling or changes in temperature and has been used by many doctors to confirm CRPS/RSD, although that is now considered less than reliable for diagnostic purposes.