Detection of Osteoporotic Changes in Rat Femoral Bone Using the Acoustically Stimulated Electromagnetic (ASEM) Method

Bone exhibits piezoelectricity originating from the alignment of collagen fibers, enabling detection of acoustically induced electric polarization through the acoustically stimulated electromagnetic (ASEM) method. In this technique, piezoelectric polarization is modulated at the radio frequency of ultrasound irradiation and captured by a resonant antenna precisely tuned to the frequency of the ultrasound waves. Goto-Kakizaki rats, a model of type 2 diabetes mellitus (DM), were bred for 40 wk. Their femoral bones were harvested for micro-computed tomography (micro-CT) imaging and mechanical evaluation using a three-point bending test. Additionally, osteoporosis was induced in Sprague-Dawley rats by immobilizing the right knee in a cast for 12 wk, confirmed via micro-CT. ASEM measurements revealed significantly lower signal intensities in both the metaphysis and diaphysis of femoral bones from the DM rats compared to controls. Among the mechanical parameters examined, breaking displacement showed the strongest association with ASEM signal intensity (r = 0.499, p = 0.058). Although this association did not reach statistical significance, it suggests that ASEM may be sensitive to deformation-related aspects of bone quality and warrants further investigation using direct measures of post-yield behavior. Following decalcification, ASEM signal intensity in metaphysis remained lower in the DM group than in controls. Similarly, immobilized femora exhibited a significant reduction in ASEM signal intensity in metaphysis. These findings demonstrate that ASEM signal intensity is reduced in osteoporotic bone across two models with distinct pathological backgrounds. The persistence of the between-group reduction after decalcification supports the involvement of collagen-related electromechanical alterations, although the specific collagen properties responsible remain to be identified. The present findings support the potential of the ASEM method to detect osteoporosis-associated changes in the collagen-related electromechanical response of bone and to image their spatial distribution.