Hi Leena,
I would hold to our motto 'it ain't cancer till they say it is' in this situation. In an article on kidney cancer at:
http://www.oncologychannel.com/kidneycancer/benign.shtml
it states that 7 to 22 percent of autopsy cadavers have renal adenoma, a small benign tumor of the kidney, so this could be completely unrelated to oral SCC as your doctor has said.

As far as diffent scans go, there is an article in the news section of the OCF site that describes the newest scanning technology, the CT/PET scan. It also explains the differences between the common types of scans. You can find it at:
http://www.oralcancerfoundation.org/news/story.asp?newsId=360

I had a CT scan last week and was told not to eat or drink anything 2 hours before scan time. I asked the technician about this and he said that it was because some people get nauseous from the contrast dye injection and it is to prevent vomitting and/or choking. I would ask your doctor about sipping water to confirm this, but I suspect that it would be ok.

Hope this is of some help. Good luck - Sheldon