Evaluation of 201Tl-accumulation in lung

In order to evaluate 201Tl-accumulation in lung, 201Tl imaging was performed using a scintillation camera coupling to a small digital computer, and blood clearance of it was examined. After the injection of 74MBq(2mCi) of 201Tl-chloride, the serial images and static images were obtained. In order to obtain the image of 201Tl in the extravascular space [T sub(E)(x, y)], a subtraction technique was performed as follows; after 2 anterior views of 201Tl were obtained using a 20% window centered at 80 keV[T0(x, y)] and 140 keV[T140(x, y)] respectively, and blood sample was taken, radionuclide angiocardiography with 185 MBq(5mCi) of sup(99m)Tc-human serum albumin and it's static image were done in the same supine position and blood sample was taken too. The radioactivity of 201Tl(T) and sup(99m)Tc(H sub(B)) in the blood was counted by a autogamma scintillation counter. Then the image of T sub(E)(x, y) was obtained by the following formula; T sub(E)(x, y) = T0(x, y) - [H(x, y) - T140(x, y)]T sub(B)/H sub(B). Following results were obtained; (1) The disappearance of 201Tl from the blood was rapid and 15 min after the injection only 10 -- 15% of the activity after 1 min was present in the blood. (2) The lung activity in the time activity curve decreased rapidly to reach plateau within 100 -- 150 sec after the injection. (3) The image of 201Tl in the extravascular space was nearly equal to the original one as regard to the radioactivity of 201Tl in lung. (author)