Fig. 1. (a)–(c) Image of the micro-CT of osteoporosis, normal, and enhanced bone sample, respectively. (d) The position of the sensors in simulation. A and A1 are a group, B and B1 are another group, and so on. (Ost represents for the osteoporosis bone, Nor represents for the normal bone, and Enh stands for the enhanced bone.)

Fig. 2. (Color online) (a) Normalized PA power spectrum density and linear fit of PA signal from three types of bone with different bone microstructures. (b) Normalized QUS power spectrum density and their linear fit. (c) The PA experiment spectrum. (d) The US experiment spectrum. (e) The box plot of the slope of three PA spectra and BUA from the QUS spectra. (f) The value of three PA spectral slopes versus the mean BUA of the QUS.

Fig. 3. (Color online) Normalized PA spectral parameter slope of four groups of samples. Ost1, Ost2, and Ost3 are bone samples taken as a corrosion matrix in proper order based on the normal bone.

Fig. 4. (a) Experiment setup for studying the PAs in a femur. (b) The photo of the PA experiment setup. (c) The sample of the experiment.