Combined PET/CT with Iodine-124 in Diagnosis of Mediastinal Micrometastases in Thyroid Carcinoma

摘要

Iodine-124 PET is an useful 3-dimensional imaging technique for diagnosis and management of thyroid diseases. The difficulty in interpretation of the PET scans with highly selective tracers like iodine-124, is the lack of identifiable anatomical structures, so an accurate anatomical localization of foci presenting abnormal uptake is problematic. Consequently, a combined PET/CT scanner can resolve these difficulties by co-registering PET and CT data in a single session allowing a correlation of functional and morphologic imaging.A case is presented where iodine-124 produced by a clinical cyclotron was used with a combined PET/CT scanner for clinical staging of a patient with thyroid carcinoma. Brief Report A 54-year-old male with a history of an well differentiated (G1) follicular thyroid carcinoma (1cm in diameter penetration of the thyroid capsule; pT4 pN0 MX) was referred to the Department of Nuclear Medicine for radioiodine therapy. The medical history was inconspicuous. The physical examination showed a patient in good general condition. On admission time the following pathologic laboratory values were seen: Thyreoglobulin: 1.8 ng/ml, recovery test: 68%, thyroid stimulating hormone: 68 mU/l, fT3 <2.9 ng/ml and fT4 2.8 ng/ml. Cervical ultrasonography showed no pathological structures. Prior to further treatment, an accurate staging was desired. Iodine-124 PET/CT 24 hours after the oral administration of 85 MBq of the positron-emitting radionuclide [iodine-124]-sodium-iodide [1] images on a combined PET/CT system were acquired (biograph, Siemens Medical Solutions Erlangen, Germany manufactured by CPS, Knoxville, USA). Projections from head to pelvis were obtained. The biograph consists of a single slice spiral CT (Somaton Emotion) and a dedicated full-ring PET scanner (ECAT HR+). The CT data are also used for PET attenuation correction in a 3D mode [2,3]. The PET scan alone showed pathologically increased tracer uptake in two cervically or mediastinal foci (Fig. 1, left).