Clinical assessment of the backscatter coefficient in osteoporosis

Abstract

Current commercial ultrasound "bone densitometers" process only the through-transmitted signals while failing to extract additional information contained in the scattered signals. This work was conducted to investigate the clinical interest of a backscatter ultrasound technique for bone characterization in 24 healthy premenopausal (group N), 24 postmenopausal (group PM), and 13 osteoporotic patients with fractures (group O). Pulse-echo measurements of the backscatter power were performed at the calcaneus (heel bone) using an ultrasound bone imaging scanner. The pulse-echo waveforms backscattered by the internal trabecular micro-architecture were recorded to compute the integrated backscatter coefficient (BUB, dB) in the frequency range 200-600 kHz. BUB was compared to the slope of the frequency-dependent attenuation (BUA, dB/MHz) derived from signals transmitted through the bone and to bone mineral density. Measurements were averaged in an operator-independent automatic ROI. The short-term reproducibility was 1.4%, and 3.5% for BUA, and BUB respectively. Femoral bone mass density (BMD) was measured in all subjects and calcaneal BMD was measured in a subset of 30 patients. The correlation between ultrasound and calcaneal BMD was moderate for BUB (r=0.55, p<10/sup -3/) and strong for BUA (r=0.82, p<10/sup -4/). Significant differences were found in ultrasound parameters and BMD between fracture and non-fracture groups. There was a significant difference in BMD and ultrasound parameters between young normal controls and healthy post-menopausal women. In summary, reflection ultrasound appears to be promising in osteoporosis and larger studies are clearly warranted.