Thanks to all for your replies to my question about prep for my PSMA scan on Friday (clinical trial at University of Pennsylvania). If you review them, you'll probably also be surprised at the considerable variance in the instructions/experiences reported. They range from no instructions in several instances (as in my case) to limitations on both exercise and food/water beforehand. I suspect that this variance may be attributable to differences in the particular radioisotopes/carrier compounds as well as the established SOPs of the respective providers.
I think I'll follow the median prep instructions.