patients with cold thyroid nodule were imaged with 201Tl (early 15min

delayed 120min). Regions of interest (ROIs) were generated over the cold nodule and normal tissue on each image by semi-quantification method. The semi-quantitative analysis was performed by using a lesion to non-lesion ratio of early(ER) and delayed(DR) images. Retention index(RI) was calculated by dividing delayed-early subtraction to product ER. There was significant difference in the ER

DR and RI between malignant and benign lesions (P<0.05). The difference was not significant between carcinoma and inflammation (P>0.05)

but there was significant difference between carcinoma and cystic adenoma (P<0.01).The sensitivity

specificity and accuracy using semi-quantification were significantly higher than visual method

and DR

RI were higher than ER (P<0.05). 201Tl imaging of thyroid cold nodule using ER

DR and RI have good clinical application value.