Here is the excerpt from the DHS document:<p>Individuals undergoing screening using AIT generally will have the option to decline an AIT screeningin  favor  of physical screening. Given  the  implementation  of  ATR and  the mitigation of privacy issues associated with the individual image generated by previous versions of  AIT  not  using  ATR, and  the  need  to  respond  to  potential  security  threats, TSA  will nonetheless mandate AIT screening for some passengers as warranted by security considerations in order to safeguard transportation security.