A number of news outlets are reporting today on the bizarre-sounding story of terrorist groups considering how to implant explosive devices into humans to blow up a passenger jet.

A U.S. security official confirmed the story for ProPublica, and the Transportation Security Administration released a statement that it had recently briefed domestic and foreign airlines. The agency said that passengers flying to the United States may notice additional security measures, such as more interaction from TSA officers, pat-downs and the use of “enhanced tools and technologies.”

But it was recent advances in airport security, including the use of body scanners that can see underneath clothing, that have prompted terrorist groups to find new ways to conceal explosives, the TSA said.

We wrote about the body scanners in May after a group of scientists questioned the tests that the TSA has made public to assure travelers the machines are safe. So we decided to provide some context to today’s news.

The body scanners—which use backscatter X-ray and millimeter wave technology—most likely wouldn’t detect an implanted explosive because they’re designed to find objects on the body—not inside it.

Steven W. Smith, who invented the X-ray body scanner used at checkpoints, has said that the images do penetrate slightly beneath the skin, allowing the operator to see shin bones. But they can’t see ribs or internal organs.

And while airport metal detectors frequently alarm on hip and knee implants, they would be incapable of detecting a device made of plastic.

None of the machines the TSA uses can see inside body cavities or underneath skin like a medical X-ray can. Several critics, including members of Congress, have cited this inability to challenge TSA’s plans to deploy the scanners at nearly every security lane by 2014. As an example, they point to the 2009 attack at a Saudi palace by a suicide bomber who detonated explosives secreted in his rectum.

Similar versions of the implanted-explosive threat have arisen periodically in the last few years. The British tabloid The Sun reported in March 2010 that al-Qaida discussed concealing explosives in breast implants. A report by its competitor, The Daily Mail, in December 2010 said that defense analysts had discovered terrorists debating the implant method in an online forum.

The security industry does sell X-ray machines, called transmission scanners, that can see inside body cavities and underneath skin. The Cook County sheriff in Illinois introduced such a machine, known as the RadPRO SecurPASS, at its jail in February.

Since then, guards have made some interesting finds, sheriff’s spokesman Steve Patterson said in an interview before today’s report. In one case, an inmate was found to have swallowed 10 pouches of heroin. Another was found to have kidney stones and was transported to a hospital.

There’s no indication that the TSA has considered such machines, and an agency spokesman declined to answer whether it has. But it would be extremely difficult for the TSA to gain public acceptance of such technology, given the controversy over the privacy and safety of its current body scanners.

A 2006 study by German physicists found that transmission scanners deliver a radiation dose that is 20 to 85 times higher than the backscatter scanners.

The TSA has released several assessments showing that its backscatter machines emit a low dose equivalent to two minutes of a flight at high altitude, but they have not dowsed safety concerns. Last month, the Electronic Privacy Information Center, a civil liberties group that has sued the TSA to suspend the scanner program, released documents showing concerns about cancer diagnoses among airport screeners in Boston.

The agency responded that the “cancer clusters” are a myth, noting that Boston didn’t have body scanners at the time. It also pointed to an evaluation by the National Institute for Occupational Safety and Health that concluded that the variety of cases and years of exposure made it unlikely that the cancers were caused by any TSA machine.

Although the intelligence about the implanted explosives is new, the security official told ProPublica there is nothing to indicate an imminent threat.