1. A method of determining a proportion of body materials in a body part, comprising the steps of: a) providing a device for retaining said body part; b) providing at least one reference material with at least two thicknesses, wherein each of said at least one reference material has an attenuation characteristic, and wherein said attenuation characteristic is selected in correspondence to said body materials; c) positioning said at least one reference material adjacent to said device; d) positioning at least three radiopaque markers on said at least one reference material; e) simultaneously irradiating said body part, said at least one reference material and said radiopaque markers, thereby creating beams that are attenuated by said at least one material and said body part and thereby projecting a pattern from said radiopaque markers; detecting said beams that are attenuated by said at least one reference material and said body part as attenuation values with a detector; g) determining the thickness of said body part from said pattern; h) determining said attenuation values for said at least one reference material at said determined thickness; and i) calculating said proportion of said body materials defining said body part by comparing said attenuation values of said body part to said determined attenuation values for said at least one reference material at said determined thickness.