DARPA- Funded Technologies

Low-Level Scattered X Rays and Computer Image Processing - Nicolet Imaging

Under development by Nicolet Imaging Systems of San Diego, California, this technology uses extremely low doses of scattered x rays, in conjunction with advanced computer image processing techniques, to detect weapons, explosives, illegal chemicals, and other contraband concealed under a person's clothing. An individual being scanned stands in front of the system for approximately 3 seconds. Almost immediately a computer-enhanced image appears on a monitor displaying the outline of the person and any concealed objects. Multiple views such as front, rear, and sides require individuals to turn their bodies for additional scans. The system is suitable for fixed-site configurations in controlled areas, such as prisons.

This technology requires only a fraction of the radiation level previously thought necessary to detect concealed objects. Each 3 second scan exposes a person to 3 microRem of radiation. This level compares with the 10 to 20 microRem per hour that a person receives from naturally occurring background radiation, 500 microRem per hour received during a commercial airline flight at 35,000 feet above sea level, and 30,000 to 300,000 microRem received during medical x ray examinations.

Through a process known as Compton scattering, the low-dose x rays collide with and bounce off electrons in the body or another object. When the x rays penetrate materials composed of elements with a low atomic number, such as body tissue, they are more likely to bounce back, causing the image on the monitor to appear light. However, when x rays pass through materials with a high atomic number composition, such as metal or bone, the radiation is more likely to release energy through the photoelectric effect, producing a dark image on the screen. Thus, a concealed handgun would appear as a dark mass against the light background of a person s body. Because of the low dose used in this method, most of the radiation reaches only the skin or penetrates a few centimeters into the body. The bones of the lower legs are the only internal structures likely to show up on the monitor, because they are so close to the skin.

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