hi psychee,
The doctor should not treat you any differently because you have said 'no'. That is part of informed consent. That you can say 'no' and it will not effect the treatment you receive. One of my doctors asked once if he could take a picture of a rash because it was a perfect representation of that type of rash an he was writing a book. I told him he could as long as I could see the picture. He took the picture and then showed it to me. There was no indication that it was me. So I told him he could use it. But I think my doctor would have been totally fine if I had said 'no'. There was one time there was a student doctor working at my health clinic and the doctor asked me if she could watch my pap test. I said 'no' and they were totally okay with that.

I'm sure your doctor is the same way. You are not the only person who would have told him 'no'. Doctors and researchers know this.