The purpose of this study is to see how a new tracer named 18F-MFBG (Meta Fluorobenzyl Guanidine) behaves in the body after injection, how it spreads to all the organs and how it is removed from the body. We will also study how long 18F-MFBG lasts in the blood after administered. In addition we want to study if 18F-MFBG can show Neuroendocrine tumors on a PET-CT scan.