Positron Emission Tomography (P.E.T.) Scanning for diagnosis, recurrence

I'm writing from a facility that performs P.E.T. Scans. For those of you not familiar with this scan, it is an invaluable tool that reveals metastatic disease that other imaging techniques simply cannot detect. It shows the progress of the disease and how the body responds to treatment. It assists physicians in providing more appropriate treatment plans and allows for earlier detection. Until there is a cure, early detection is the next best thing. With an injection of glucose containing a signal-emitting tracer, the scanner records signals that the tracer emits as they journey through the body and collects in the various organs targeted for examination. A computer reassembles the signals into actual images and distinguishes malignant from benign cells. As with everything new, it takes time to prove it's true value. Just like it used to be with MRI, CT's, etc.. This test can truly save lives. I am currently trying to get a patient's ins.co.to authorize a P.E.T. for recurrent thyroid ca., which is normally considered medically necessary with elevated thyroglobulin levels. This patient does not have elevated tg levels, but has had recurrence of the disease twice. Has anyone been diagnosed or have had recurrence without elevated thyroglobulin? Thank you for your responses and input. Shelley