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; removing attenuation due to pixels corresponding to air inside the exposed subject in the one or more scout images without removing the pixels by comparing each pixel to air attenuation of a free trajectory 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.