Inclusion criteria:
a) patients with differentiated thyroid cancer after thyroidectomy
b) patients that had received 131I therapy and have no/inadequate correltive on scintigraphy
c) increased/presistant levels of thyroglobulin
d)18 years old and older
Exclusion criteria:
a) pregnacny or lactation
b) inability to consent
c) synchronous second malignancy