Methods for assigning a threat or safe condition to an object in an image

A method for assigning one of a safe condition and a threat condition to an unknown object, the method comprising the steps of:

• determining a density value and an effective atomic number value for a plurality of predetermined safe objects and a plurality of predetermined threat objects;
• plotting the density value and effective atomic number values of each of the predetermined safe objects and predetermined threat objects in a probability map to correlate corresponding pairs of density values and effective atomic number values with each of the predetermined safe objects and predetermined threat objects;
• scanning an unknown object to provide a plurality of dual-energy attenuation images each having dual-energy attenuation information representing the unknown object;
• decomposing each of the dual-energy attenuation images into dual-reference material equivalent path length images to provide reference material equivalent path lengths representing the unknown object;
• converting the reference material equivalent path lengths representing the unknown object into unknown object path lengths multiplied by a predetermined scaling factor;
• determining the effective atomic number for each pixel representing the unknown object;
• and,
• imposing the effective atomic number of the unknown object and the mass density of the unknown object on the probability map to determine a probability that the unknown object is correlated with one of a predetermined safe object or a predetermined threat object.