There are two types of full-body scanners . Forty such scanners are currently in use at all U.S. airports . The TSA has purchased an additional 30 machines . Currently use of the machines is optional , according to NASA 's web site .
Forty such scanners are currently in use at all U.S. airports . The TSA has purchased an additional 30 machines . Currently use of the machines is optional , according to NASA 's web site .