Prostate cancer is the second leading cause of cancer deaths in American men. When prostate cancer is confined to the prostate there is a high chance of cure. However, it is outside the prostate or comes back after treatment, additional therapy may be needed. Current methods of imaging prostate cancer are limited. Researchers want to see if a radiotracer called 18F-DCFPyL can identify prostate cancer in patients who have a high risk of cancer spreading outside the prostate or who have signs of recurrent cancer after treatment.