Measurement of integrated backscatter coefficient of trabecular bone

Recent studies, including comparison between acoustic properties of bone tissue and bone mass density or micro-architectural parameters derived from histomorphometry have led to the conclusion that ultrasonic attenuation and velocity in the frequency range 200-600 kHz reflects mainly bone quantity, and microarchitecture to a smaller extent. Ultrasonic tissue characterization based on spectrum analysis of backscattered ultrasound has shown the potential to provide the information needed for the characterization of tissue structure. The authors' goal was to evaluate the ability of integrated backscatter coefficient (IBC) to provide additional structural information unrelated to bone mass density (BMD). Integrated backscatter coefficient was measured in the frequency range 200-600 kHz and compared to bone mass density and to ultrasonic attenuation and velocity in 15 human calcaneal (heel bone) specimens, removed from cadavers. Ultrasonic measurements were performed using a matched pair of focused broadband 0.5 MHz transducers. A standard through-transmission insertion method was used to derive the slope of frequency-dependent attenuation coefficient (known as nBUA dB/cmMHz) and ultrasonic bone velocity (UBV). IBC was measured using a reference signal on a steel plate. BMD was measured using X-ray quantitative computed tomography. BMD could explain 68% of the variability of IBC. This indicates that IBC is sensitive to bone properties in a way that BMD alone is not. Modifications of scattering with aging may be explained by the alteration of the micro-architecture of cancellous bone. Significant differences were obtained in BUA (p<0.005), UBV (p<0.005), IBC (p<0.0005), and BMD (p<0.01) among males and females. However, IBC showed a slightly higher sex-related difference than other parameters. This result might be explained by the difference in bone remodeling with aging which is usually observed in men and women.