Is there a way to invert a CT scan in volume rendering?

Hello, I am trying to filter out high density material in volume rendering so the low density material is visible, however when I increase the shift toggle it does the opposite of what I want (making the low density material more transparent and the high density material more clear). I would like it if I could filter out the high density material. Is there a way to invert the properties of the CT scan (or something similar) so that the high density material would become more transparent?