Airport security devices are now very sensitive
Medical scans can render people radioactive enough to trigger false security alarms at airports for up to a month, a Lancet piece warns.
Over 18 million scans using radioactive versions of common elements are carried out in the UK each year.
They include tests of the thyroid gland, bone, and blood flow to the heart muscle.
Professor Richard Underwood, of London's Royal Brompton Hospital, said the side effects should be made clear.
He called for patients to be issued with standard information cards about their scan if it made use of radioisotopes.
The Lancet piece highlights the case of a 55-year-old commercial pilot referred for cardiac investigation.
Doctors carried out a scan using a radioisotope of the element thallium.
Two days after the scan the patient travelled to Moscow as a crew member.
While passing through customs, the radiation detector alarms were triggered, and the patient was detained for questioning.
After extensive interrogation, he was released, but experienced the same problem at the same airport four days later.
Eventually the airport security officials gave him a card to carry while travelling that explained his scan was to blame.
More sensitive systems
Professor Underwood said: "Stricter measures, and more sensitive radiation detection systems, are being deployed at airports worldwide.
"It is important to warn patients having had a thallium scan that they may trigger radiation detectors for up to 30 days.
"It should be standard practice to issue patients with an information card after diagnostic or therapeutic procedures involving radioisotopes."
Professor Underwood said the card should state the date and place of the procedure, the radioisotope used and its half-life, potential duration of radioactive emissions from the patient, and details on who to contact for verification if necessary.
"Patient information cards could lessen the impact of such false alarms and avoid unnecessary interrogations by airport security personnel."
Professor Adrian Dixon, of the Royal College of Radiologists, said many cardiac units had switched from using thallium, which has a relatively long half life, to another element, technetium, which does not linger so long in the body.
Professor Dixon said many units made patients aware the possible side effects following a scan.
But he added: "It is good that this paper will make people more aware of the issue."