1. A computer-implemented method to determine a water equivalent diameter of an exposed subject, the method comprising: receiving image data comprising one or more scout images of the exposed subject from an image acquisition device; identifying, using a processor, objects in the one or more scout images; segmenting, using a processor, the exposed subject in the one or more scout images; determining pixels corresponding to air by comparing each pixel to the air threshold value in the one or more scout images; determining pixels corresponding to each object identified in the one or more scout images; isolating subject attenuation parameters in the one or more scout images; computing, using the processor, the water equivalent diameter of the exposed subject in the one or more scout images.