The purpose of the study is to investigate how uptake counts of ²⁰¹Tl of radioisotopes in the human body could change, when taking computed tomography and magnetic resonance imaging right after injecting contrast media. ²⁰¹Tl radioisotope substances of iodine contrast medium, which is a computed tomography contrast medium, and paramagnetic contrast medium, which is an magnetic resonance imaging contrast medium, were used as study materials. First, ²⁰¹Tl was put into 4 cc of normal saline in test tube, and then a computed tomography contrast medium of Iopamidol^® or Dotarem^®, was put into 2 cc of normal saline in test tube. An magnetic resonance imaging contrast medium of Primovist^® or Gadovist^® was also put into 2 cc of normal saline in test tube. Each contrast medium was distributed to make ²⁰¹Tl as 3 mCi, with a total of 4 cc. Gamma camera, low energy high resolution collimator, and pinhole collimator were used to obtain images. The uptake count of ²⁰¹Tl was measured with 1000 frames of images, and obtained after 10 times of repetition. This study revealed that the use of Gadovist^®, which is an magnetic resonance imaging contrast medium, showed the smallest number of uptake count, after measuring ²⁰¹Tl uptake count by low energy high resolution collimator. On the other hand, the use of Iopamidol^®, which is a computed tomography contrast medium, showed the biggest difference in uptake count, when measuring ^99mTc uptake count by Pinhole collimator. When examining with gamma camera, using contrast medium and ²⁰¹Tl, identifying the changes of uptake count is very important for improving the value of diagnosis.