Provided herein are imaging agents, antidotes to the imaging agents and methods of using the same to image a thrombus or blood clot or thrombin including sites of thrombin accumulation and to diagnose and treat thrombosis. The imaging agents include an aptamer capable of binding the thrombus or thrombin in particular linked to a reporter moiety. The imaging agents may be used to label the thrombus or sites of thrombin accumulation. Antidotes capable of binding to the aptamer in the imaging agent are also provided. The antidotes may further be linked to a quencher capable of quenching the reporter moiety.