Management of patients with thyroid carcinoma: application of thallium-201 scintigraphy and magnetic resonance imaging Thyroid carcinoma has the ability to concentrate radioiodine, an attribute that can be used both for detection of thyroid cells and for treatment. Unfortunately, however, radioiodine uptake is not observed in all patients and a radioiodine scan requires that the patient be rendered hypothyroid for 4-6 wk. In the present study, we analyzed the utility of thallium-201 scanning and the usefulness of magnetic resonance imaging (MRI) in the detection of thyroid cancer. Nineteen patients with thyroid cancer had a total of 24 radioiodine scans, 33 thallium scans, and 10 MRI examinations. Of the 19 patients in the study, 17 had differentiated thyroid carcinoma. In these 17 cases, all paired studies were concordant for the presence (n = 7) or absence (n = 10) of disease. However, in one case (Patient 10), the 201Tl studies showed far more extensive disease than was observed on the 131I scan. Thyroid cancer was also detected on seven MRI studies. In summary, thallium and MRI scans are adjunctive techniques to radioiodine scanning that can either confirm the presence of neck bed activity, residual disease or metastatic cancer and may delineate tumor deposits not detected by radioiodine scanning. Thallium may be capable of detecting tumor deposits even while a patient remains euthyroid. 