Detection of lung lesions and lymph nodes with 201Tl SPET.

The aim of this study was to characterize lung lesions by means of the uptake, retention and washout of 201 Tl, and to quantify the sensitivity of 201 Tl SPET (single photon emission tomography) in detecting mediastinal and hilar lymph nodes. A total of 68 patients with lung lesions (tumours and inflammation) underwent both helical computed tomography (CT) and 201 Tl SPET examinations. Uptake, retention and washout parameters were calculated from early and delayed 201 Tl SPET by drawing regions of interest over the primary lesion and the background of the lung. The findings on 201 Tl SPET were compared with those on CT and surgical findings. A significant difference in the retention index (RI) was observed between primary malignant and benign lesions. In detecting lymph nodes, the sensitivity, specificity and negative predictive value were 83%, 60% and 90% respectively for early 201 Tl SPET, and 50%, 80% and 80% respectively for delayed 201 Tl SPET. 201 Tl SPET with semi-quantitative analysis, especially RI, helps to differentiate between malignant and benign lung lesions. Lymph nodes larger than 1 cm on CT but not showing 201 Tl uptake could be considered non-metastatic lesions.