X-ray imagers, on the other hand, can only pick out objects made from dense materials. They can detect the shape of a knife or gun, but the radiation sails right through softer substances such as drugs or plastic explosives.
If "terahertz imager" sounds familiar, it may be because some airport scanners rely on this technology, instead of x rays, to see through clothing. Anyone who has been through the airport security line, and has been asked to step into the chamber and put her arms up over her head for three seconds has probably been inside a terahertz body scanner. (There are other ones that use low doses of x-ray radiation, but they're slowly being phased out.)
Unfortunately, terahertz scanners aren't able to produce video. That's why people have to stand still for three seconds.
Trichopoulos' camera can create video. His technology uses a sensor that contains thousands of miniscule antennas, each less than a tenth of a millimeter across. Those antennae pick up the terahertz radiation. Terahertz radiation is all around us, reflecting off objects, but it's not often "bright" enough for the sensor to pick up quickly. So the terahertz video camera has a transmitter that beams terahertz waves at the object it wants to scan, just as a TV camera might use spotlights to illuminate the subject.