The FAA have updated their page summarizing the evaluation of the four FOD detection systems. They also link to the relevant FAA circulars.
The FAA evaluated four types of automated FOD detection systems at four large US airports, including the Theodore Francis Green State Airport in Providence, Rhode Island, Boston Logan International Airport, Chicago O’Hare, and Chicago’s Midway Airport. The four different FOD detection systems were installed and evaluated at one of these airports. Key operational characteristics of each FOD detection system were evaluated, documented, summarized, and then published as FAA Final Reports, which are available, as they are published, on this web site under Downloads-Safety. Specific issues that were looked at include the system’s ability to located FOD items, accuracy, speed, and capability to trigger alerts to airport personnel.
Source (FAA)