Two-dimensional quantitative analysis of point focus X-ray beam diffraction was performed using a transmission optics system to examine the biological apatite (BAp) orientation in the femurs of an osteopetrotic (op/op) mouse and a normal mouse. The Mo Kα (wavelength: 0.07107 nm) was used as characteristic X-ray radiation as a substitute for conventional Cu Kα (wavelength: 0.15418 nm) radiation. At first a theoretical calculation concerning with X-ray absorption and peak resolution was performed, and subsequently X-ray diffraction measurements were carried out to confirm the usefulness of the transmission X-ray method by Mo Kα radiation. The distribution of the preferential orientation of the BAp c-axis was finally measured and calculated as an integrated intensity ratio of (002)/(310) in a plane roughly containing the bone longitudinal axis. The result resembled analysis from a conventional reflection X-ray diffraction method by Cu Kα radiation but this transmission optics system was more convenient for the screening of BAp orientation in bones without sectioning.
   The distribution of the preferential alignment of the BAp c-axis was measured as a function of the longitudinal axis in the femurs of a 12-week mutant op/op mouse and a littermate control mouse. The preferential alignment of the BAp c-axis along the longitudinal direction is much lower in the op/op mouse than in the control mouse in all analytical positions. The transmission optics system using Mo Kα radiation in this study provides a fuss-free method for analyzing BAp orientation as a bone quality parameter.