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The next step is to convert the images from x-ray intensities to an "apparent thickness" (not a real scientific term, thus the quotes). I use this term to refer to how much "stuff" the beam passes through. This conversion is done using the equations above. The first shows that the intensity after passing through the bone depends on the initial intensity and the negative exponential of the apparent thickness (mu is the attenuation constant of the material and x is the length of the material). We solve for this apparent thickness, resulting in the second equation. However, we must find the initial beam intensity, which we will calculate for each row individually.