Washington ? High-tech security scanners that might have prevented the Christmas Day attempt to blow up a jetliner have been installed in only a small number of airports around the world, in large part because of privacy concerns over the way the machines see through clothing.

The body-scanning technology is in at least 19 U.S. airports, while European officials have generally limited it to test runs.

Umar Farouk Abdulmutallab, the Nigerian accused of trying to ignite explosives aboard a Northwest Airlines jet as it was coming in for a landing in Detroit, did not go through such a scan where his flight began, at Amsterdam’s Schiphol airport.

The full-body scanner “could have been helpful in this case, absolutely,” said Evert van Zwol, head of the Dutch Pilots Association.

But the technology has raised significant concerns among privacy watchdogs because it can show the body’s contours with embarrassing clarity. Those fears have slowed the introduction of the machines.