The potential of ^99mTc labeled P^1, P^4-di （adenosine-5 ＇ ）-tetraphosphate （Ap4A） for imaging experimental atherosclerotic plaques was evaluated in New Zealand white （NZW） rabbits. To label the ^99mTc to Ap4A, stannous tartrate solution was used. ^99mTc-Ap4A was purified on a Sephadex G-25 column. The radiochemistry purities of ^99mTc-Ap4A were 85% to 91%. Biodistribution study revealed ^99mTc-Ap4A cleared from blood rapidly. Thirty min after ^99mTc-Ap4A administrated on NZW atherosclerotic rabbits, lesion to blood （target/blood, T/B） ratio was 3. 17 ±1.27, and lesions to normal （target/non-target, T/NT） ratio was 5.23 ±1.87. Shadows of atherosclerotic plaques were clearly visible on radioautographic film. Aortas with atherosclerotic plaques also could be seen on ex vivo gamma camera images. Atherosclerotic abdominal aortas were clearly visible on in vivo images 15 min to 3 h after ^99mTc-Ap4A administration. ^99mTc-labeled Ap4A can be used for rapid noninvasive detection of experimental atherosclerotic plaque.
