Clinical evaluation of 201Tl single photon emission computed tomography in patients with large opacities due to silicosis and in those with bronchogenic carcinoma

201Tl single photon emission computed tomography (201Tl SPECT) was used to evaluate 18 patients with large opacities due to silicosis and 22 others with bronchogenic carcinoma. An early scan and a delayed scan were obtained and the retention index was calculated from the early ratio and the delayed ratio. In patients with silicosis, the retention index and the two ratios were significantly lower than in the patients with bronchogenic carcinoma (p<0.01). In patients with stable shadows on chest X-ray films due to large opacities of silicosis, the delayed ratio was the same as or lower than the early ratio. However, in patients with silicosis who had high activity in large opacities, the delayed ratio was higher than the early ratio. These results suggest that 201Tl SPECT is useful for evaluating the activity of large opacities in patients with silicosis and for differentiating large opacities caused by silicosis from those caused by bronchogenic carcinoma. (author)