A novel Sampling Sphere Orientation Distribution (SSOD) method based on mobile sampling spheres is developed for describing microstructural anisotropy of trabecular bone using grayscale images. Efficient implementation of SSOD on segmented and unsegmented 3D SymbolCT images of human trabecular bone samples from different anatomical locations is demonstrated. The second order fabric tensor of SSOD corresponds well with the one derived from the mean intercept length (MIL) method applied on segmented images. The results of SSOD are extended to higher order fabric approximations and the effect of sampling sphere radius is examined. Finally, performance of the method on artificial microstructures is presented.