"There are currently 500 body scanners, split about evenly between the two technologies, deployed in airports. The TSA plans to deploy 1,275 backscatter and millimeter-wave scanners covering more than half its security lanes by the end of 2012 and 1,800 covering nearly all lanes by 2014."

potential risk to such a huge contract with a company Chertoff is profiting from seems like a pretty darn good reason to delay the study.