RESUMEN
<p><b>OBJECTIVE</b>To investigate the diagnostic value of dual-head (18)F-fluorodeoxyglucose ((18)F-FDG) imaging in metastatic lesion with unknown primary tumour (UPT).</p><p><b>METHODS</b>Seventy patients with UPT underwent dual-head (18)F-FDG imaging after iv (18)F-FDG 1.85 MBq/kg. The primary tumour was diagnosed according to the FDG uptake and T/N value.</p><p><b>RESULTS</b>Of the 70 patients, the primary tumour was identified by positive FDG imaging and finally confirmed pathologically in 58 patients (82.9%), and 12 patients had a negative FDG imaging (17.1%). Forty-two of the 58 positive patients were found to have lung cancer (72.4%). Among the 12 negative patients, their primary tumour was then identified by other diagnostic procedures in 5 patients (41.7%), in 1 patient, the primary site was detected during follow-up, however, the primary tumour was never detected in the rest 6 patients.</p><p><b>CONCLUSION</b>Dual-probe (18)F-FDG imaging is a simple, quick, non-invasive and sensitive technique with an accuracy over 80% in the diagnosis of unknown primary tumour. The lung is found to be the most frequent primary site. Dual-probe (18)F-FDG imaging can be recommended as the first diagnostic choice for UPT.</p>