Tl-201 stress tests and homeland security

Background: This study estimates the length of time a patient might trigger security radiation detection devices after thallium 201 cardiac imaging. The US Department of Homeland Security is supporting the purchase and deployment of radiation detection pagers and portal monitors. Concurrently, there are an increasing number of cardiac perfusion imaging studies being performed using Tl-201. Therefore there is a higher probability that patients who have undergone nuclear medicine procedures could trigger alarms resulting in security questions. Methods and Results: The length of time patients could trigger such devices is estimated based on the radiopharmacokinetics of Tl-201 and potential radioactive contaminants as well as the capabilities of current sensitive radiation detection devices, assuming the radioactive sources are distributed in and attenuated by the patient. It is estimated that patients may trigger portable pager devices for up to 33 days and may trigger portal detectors for up to 51 days after studies using Tl-201. This is much longer than length of time for a patient to trigger such alarms after technetium 99m myocardial imaging tests, which is potentially up to 6 days. Conclusions: It should be standard practice for patients to be issued information cards that indicate the potential time for triggering security radiation detectors after diagnostic cardiac procedures involving the use of Tl-201 or other radiopharmaceuticals.